Catchup results for cond-mat from Sun, 8 Mar 2020
- Mon, 9 Mar 2020
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Mon, 9 Mar 2020
- arXiv:2003.02847 [pdf, other]
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Title: Topological superconductivity, ferromagnetism, and valley-polarized phases in moire systems: An RG analysis for twisted double bilayer grapheneComments: 11 pages, 6 figuresSubjects: Strongly Correlated Electrons (cond-mat.str-el); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Superconductivity (cond-mat.supr-con)
Recent experiments have observed possible spin- and valley-polarized insulators and spin-triplet superconductivity in twisted double bilayer graphene, a moire structure consisting of a pair of Bernal-stacked bilayer graphene. Besides the continuously tunable band widths controlled by an applied displacement field and twist angle, these moire bands also possess van Hove singularities near the Fermi surface and a field-dependent nesting which is far from perfect. Here we carry out a perturbative renormalization group analysis to unbiasedly study the competition among all possible instabilities in twisted double bilayer graphene and related systems with a similar van Hove fermiology in the presence of weak but finite repulsive interactions. Our key finding is that there are several competing magnetic, valley, charge, and superconducting instabilities arising from interactions in twisted double bilayer graphene, which can be tuned by controlling the displacement field and the twist angle. In particular, we show that spin- or valley-polarized uniform instabilities generically dominate under moderate interactions smaller than the band width, whereas spin-triplet topological superconductivity and exotic spin-singlet modulated paired state become important as the interactions decrease. Realization of our findings in general moire systems with a similar van Hove fermiology should open up new opportunities for manipulating topological superconductivity and spin- or valley-polarized states in highly tunable platforms.
- arXiv:2003.02850 [pdf, other]
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Title: Possible superconductivity with Bogoliubov Fermi surface in lightly doped Kagome U(1) spin liquidComments: 4.5 pages, 3 figures + supplement materialSubjects: Superconductivity (cond-mat.supr-con); Strongly Correlated Electrons (cond-mat.str-el)
Whether the doped t-J model on the Kagome lattice supports exotic superconductivity has not been decisively answered. In this paper, we propose a new class of variational states for this model and perform large-scale variational Monte Carlo simulation on it. The proposed variational states are parameterized by the SU(2)-gauge-rotation angles, as the SU(2)-gauge structure hidden in the Gutzwiller-projected mean-field ansatz for the undoped model is broken upon doping. These variational doped states smoothly connect to the previously studied U(1) $\pi$-flux or $0$-flux states, and energy minimization among them yields a chiral noncentrosymmetric nematic superconducting state with $2 \times 2$-enlarged unit cell. Moreover, this pair density wave state possesses a finite Fermi surface for the Bogoliubov quasi particles. We further study experimentally relevant properties of this intriguing pairing state.
- arXiv:2003.02852 [pdf, other]
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Title: Superconducting islands with semiconductor-nanowire-based topological Josephson junctionsComments: 18 pages, 17 figures. See also accompanying paper arXiv:2003.02858Subjects: Superconductivity (cond-mat.supr-con); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We theoretically study superconducting islands based on semiconductor-nanowire Josephson junctions and take into account the presence of subgap quasiparticle excitations in the spectrum of the junction. Our method extends the standard model Hamiltonian for a superconducting charge qubit and replaces the Josephson potential by the Bogoliubov-de Gennes Hamiltonian of the nanowire junction, projected onto the relevant low-energy subgap subspace. This allows to fully incorporate the coherent dynamics of subgap levels in the junction. The combined effect of spin-orbit coupling and Zeeman energy in the nanowires forming the junction triggers a topological transition, where the subgap levels evolve from finite-energy Andreev bound states into near-zero energy Majorana bound states. The interplay between the microscopic energy scales governing the nanowire junction (the Josephson energy, the Majorana coupling and the Majorana energy splitting), with the charging energy of the superconducting island, gives rise to a great variety of physical regimes. Based on this interplay of different energy scales, we fully characterize the microwave response of the junction, from the Cooper pair box to the transmon regimes, and show how the presence of Majoranas can be detected through distinct spectroscopic features.
- arXiv:2003.02856 [pdf, other]
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Title: Explicit Construction of Local Conserved Quantities in the XYZ Spin-1/2 ChainComments: 23 pages, 4 figuresSubjects: Statistical Mechanics (cond-mat.stat-mech); Mathematical Physics (math-ph); Exactly Solvable and Integrable Systems (nlin.SI)
We present a rigorous explicit expression for an extensive number of local conserved quantities in the spin-1/2 XYZ chain with general coupling constants. Moreover, in the case of the XXZ chain, we show that local conserved quantities constructed are conserved even though a magnetic field in the z-axis direction exists.
- arXiv:2003.02858 [pdf, other]
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Title: Majorana oscillations and parity crossings in semiconductor-nanowire-based transmon qubitsComments: 6 pages, 3 Figures. See also accompanying paper arXiv:2003.02852Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Superconductivity (cond-mat.supr-con)
We show that the microwave (MW) spectra in semiconductor-nanowire-based transmon qubits provide a strong signature of the presence of Majorana bound states in the junction. This occurs as an external magnetic field tunes the wire into the topological regime and the energy splitting of the emergent Majorana modes oscillates around zero energy owing to spatial overlap in finite-length wires. In particular, we discuss how the zero-energy fermion parity crossings arising from Majorana oscillations result in distinct spectroscopic features. In split-junction geometries, the plasma mode couples to the phase-dispersing subgap levels resulting from Majorana hybridization via a Jaynes-Cummings-like interaction. As a consequence of this interaction, higher order plasma excitations in the junction inherit Majorana properties, including the $4\pi$ effect. Our results, based on a fully microscopic description of the junction, suggest that MW spectroscopy of nanowire-based transmon qubits provides an interesting alternative to Majorana detection by transport spectroscopy.
- arXiv:2003.02872 [pdf, other]
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Title: Lattice glass model in three spatial dimensionsComments: 6 pages, 7 figuresSubjects: Statistical Mechanics (cond-mat.stat-mech); Disordered Systems and Neural Networks (cond-mat.dis-nn)
The nature of thermodynamic glass transition has been hindered by the lack of proper models beyond mean-field theories. Here, we propose a three-dimensional lattice glass model on a simple cubic lattice that exhibits the typical dynamics observed in fragile supercooled liquids such as two-step relaxation, super-Arrhenius growth in the relaxation time, and dynamical heterogeneity. Using advanced Monte Carlo methods, we compute the thermodynamic properties deep inside the glassy temperature regime, well below the onset temperature of the slow dynamics. The specific heat has a finite jump towards the thermodynamic limit with critical exponents close to those expected from the hyperscaling and the random first-order transition theory for the glass transition. We also study an effective free energy of glasses, the Franz--Parisi potential, as a function of the overlap between equilibrium and quenched configurations. The effective free energy indicates the existence of a first-order phase transition, consistent with the random first-order transition theory. These findings strongly suggest that the glassy dynamics of the model has its origin in thermodynamics.
- arXiv:2003.02876 [pdf, other]
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Title: General description for nonequilibrium steady states in periodically driven dissipative quantum systemsComments: 5 pages, 2 figures + supplementalSubjects: Statistical Mechanics (cond-mat.stat-mech); Optics (physics.optics); Quantum Physics (quant-ph)
Laser technology has developed and accelerated photo-induced nonequilibrium physics from both scientific and engineering viewpoints. The Floquet engineering, i.e., controlling material properties and functionalities by time-periodic drives, is one of the forefronts of quantum physics of light-matter interaction, but limited to ideal dissipationless systems. For the Floquet engineering extended to a variety of materials, it is vital to understand the quantum states emerging in a balance of the periodic drive and energy dissipation. Here we derive the general description for nonequilibrium steady states (NESS) in periodically driven dissipative systems by focusing on the systems under high-frequency drive and Lindblad-type dissipation with the detailed balance condition. Our formula correctly describes both the time-average and fluctuation of the NESS for arbitrary strengths of dissipation. Our approach will play fundamental roles in Floquet engineering in a broad class of dissipative quantum systems such as atoms and molecules, mesoscopic systems, and condensed matters.
- arXiv:2003.02880 [pdf, other]
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Title: Evidence of Lifshitz transition in thermoelectric power of ultrahigh mobility bilayer grapheneSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Resolving low-energy features in the density of states (DOS) holds the key to understanding wide variety of rich novel phenomena in graphene based 2D heterostructures. Lifshitz transition in bilayer graphene (BLG) arising from trigonal warping has been established theoretically and experimentally. Nevertheless, the experimental realization of its effects on the transport properties has been challenging because of its relatively low energy scale ($\sim 1$ meV). In this work, we demonstrate that the thermoelectric power (TEP) can be used as an effective probe to investigate fine changes in the DOS of BLG. We observe additional entropy features in the vicinity of the charge neutrality point (CNP) in gapped BLG. This apparent violation of Mott formula can be explained quantitatively by considering the effects of trigonal warping, thereby serving as a possible evidence of a Lifshitz transition.
- arXiv:2003.02888 [pdf, other]
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Title: Competing pairing interactions responsible for the large upper critical field in a stoichiometric iron-based superconductor, CaKFe$_4$As$_4$Authors: Matthew Bristow, William Knafo, Pascal Reiss, William Meier, Paul C. Canfield, Stephen J. Blundell, Amalia I. ColdeaComments: to appear in Physical Review B (2020); 13 pages, 9 figuresSubjects: Superconductivity (cond-mat.supr-con); Strongly Correlated Electrons (cond-mat.str-el)
The upper critical field of multiband superconductors is an important quantity that can reveal the details about the nature of the superconducting pairing. Here we experimentally map out the complete upper critical field phase diagram of a stoichiometric superconductor, CaKFe$_4$As$_4$, up to 90T for different orientations of the magnetic field and at temperatures down to 4.2K. The upper critical fields are extremely large, reaching values close to ~3$T_c$ at the lowest temperature, and the anisotropy decreases dramatically with temperature leading to essentially isotropic superconductivity at 4.2K. We find that the temperature dependence of the upper critical field can be well described by a two-band model in the clean limit with band coupling parameters favouring intraband over interband interactions. The large Pauli paramagnetic effects together with the presence of the shallow bands is consistent with the stabilization of an FFLO state at low temperatures in this clean superconductor.
- arXiv:2003.02889 [pdf, ps, other]
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Title: On lowest energy states of $O(N)$ fermionic chainAuthors: Tigran HakobyanComments: 11 pagesSubjects: Strongly Correlated Electrons (cond-mat.str-el); Mathematical Physics (math-ph)
A quite general finite-size chain of fermions with $N$ internal degrees of freedom (flavors) and $O(N)$ symmetry is considered. In case of the free boundary condition, we prove that the ground state in the invariant sector with $m$ odd flavors is represented by a single rank-$m$ antisymmetric multiplet. For the even-length chains, its particle-hole quantum number (if is a good one) is given by the parity of the $m$. For the odd-length chains, the particle-hole symmetry leads to the twofold degeneracy among the conjugate multiplets. Similar statements are proven for the $O(N)$ mixed-spin chains in antisymmetric representations. The results are extended to the long-range interacting fermions and (partially) to the translation invariant chains.
- arXiv:2003.02898 [pdf]
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Title: Superconducting Nanowire Fabrication on Niobium Nitride using Helium Ion IrradiationAuthors: Glenn D. Martinez, Drew Buckley, Ilya Charaev, Andrew Dane, Douglas E. Dow, Karl K. BerggrenSubjects: Superconductivity (cond-mat.supr-con); Applied Physics (physics.app-ph)
Superconducting devices are prone to reduced performance caused by impurities and defects along the edges of their wires, which can lead to local current crowding. In this study, we explored the use of helium ion irradiation to modify the lattice structure of the superconducting material to change its intrinsic properties. The process will allow us to directly pattern devices and potentially improve the quality of the nanowires. To achieve this, we used the ion beam from a scanning helium ion microscope (HIM) to localize damage on a superconducting material to create a nanowire. Two experiments were performed in this study. First, a range of helium ion doses was exposed on a niobium nitride (NbN) microwire to determine the estimated dose density to suppress superconductivity. Using the results of this first experiment, nanowires were patterned onto a microwire, and the current-voltage characteristics were measured for each sample. Our results showed that helium ion irradiation is an effective resistless fabrication method for superconducting nanowires.
- arXiv:2003.02911 [pdf, other]
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Title: Towards an information-theory for hierarchical partitionsComments: 12 pages, 5 figuresSubjects: Information Theory (cs.IT); Statistical Mechanics (cond-mat.stat-mech); Machine Learning (cs.LG); Machine Learning (stat.ML)
Complex systems often require descriptions covering a wide range of scales and organization levels, where a hierarchical decomposition of their description into components and sub-components is often convenient. To better understand the hierarchical decomposition of complex systems, in this work we prove a few essential results that contribute to the development of an information-theory for hierarchical-partitions.
- arXiv:2003.02914 [pdf, other]
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Title: Charge-, salt- and flexoelectricity-driven anchoring control in nematicsComments: 11 pages, 7 figuresSubjects: Soft Condensed Matter (cond-mat.soft); Statistical Mechanics (cond-mat.stat-mech); Chemical Physics (physics.chem-ph)
We show that the design of electric double layers and flexoelectricity can be used to tune the surface anchoring in general nematic fluids. Specifically, we demonstrate for a nematic electrolyte that the surface anchoring strength can be efficiently controlled by the surface charge, bulk ion concentration and/or flexoelectricity, effectively changing not only the magnitude of the anchoring but also the anchoring type, such as from planar to tilted. This tuning is driven by the competing energetic-torque couplings between nematic director and the emergent electrostatic potential, due to surface charge, ions and flexoelectricity. Our findings propose a novel way of influencing surface anchoring by using electrostatic effects, which could be used in various aspects, including in the self-assembly of colloidal particles in nematic fluids, optical and display patterns, and sensing.
- arXiv:2003.02918 [pdf, other]
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Title: Sharp disentanglement in holographic charged local quenchAuthors: Dmitry S. AgeevComments: 22 pages, 8 figuresSubjects: High Energy Physics - Theory (hep-th); Statistical Mechanics (cond-mat.stat-mech); Strongly Correlated Electrons (cond-mat.str-el); Quantum Physics (quant-ph)
We propose a charged falling particle in an AdS space as a holographic model of local charged quench generalizing model of arXiv:1302.5703. The quench is followed by evolving currents and inhomogeneous distribution of chemical potential. We derive the analytical formula describing the evolution of the entanglement entropy. At some characteristic time after the quench, we find that the entanglement shows a sharp dip. This effect is universal and independent of the dimension of the system. At finite temperature generalization of this model, we find that multiple dips and ramps appear.
- arXiv:2003.02945 [pdf, other]
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Title: Rounded Layering Transitions on the Surface of IceComments: 6 pages + 3 figures + supplementary fileJournal-ref: Physical Review Letters, 124, 065702 (2020)Subjects: Soft Condensed Matter (cond-mat.soft); Statistical Mechanics (cond-mat.stat-mech); Chemical Physics (physics.chem-ph)
Understanding the wetting properties of premelting films requires knowledge of the film's equation of state, which is not usually available. Here we calculate the disjoining pressure curve of premelting films, and perform a detailed thermodynamic characterization of premelting behavior on ice. Analysis of the density profiles reveals the signature of weak layering phenomena, from one to two and from two to three water molecular layers. However, disjoining pressure curves, which closely follow expectations from a renormalized mean field liquid state theory, show that there are no layering phase transitions in the thermodynamic sense along the sublimation line. Instead, we find that transitions at mean field level are rounded due to capillary wave fluctuations. We see signatures that true first order layering transitions could arise at low temperatures, for pressures between the metastable line of water/vapor coexistence and the sublimation line. The extrapolation of the disjoining pressure curve above water vapor saturation displays a true first order phase transition from a thin to a thick film consistent with experimental observations.
- arXiv:2003.02949 [pdf, other]
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Title: Giant Thermal Enhancement of the Electric Polarization in Ferrimagnetic BiFe$_{1-x}$Co$_{x}$O$_{3}$ Solid Solutions Near Room TemperatureComments: 6 pages, 4 figuresSubjects: Materials Science (cond-mat.mtrl-sci)
Thermal excitations typically reduce the electric polarization in ferroelectric materials. Here, we show by means of first-principles calculations that multiferroic BiFe$_{1-x}$Co$_{x}$O$_{3}$ solid solutions with $0.25 \le x \le 0.50$ (BFCO) represent a noteworthy exception to this behaviour. In particular, we find that at room temperature and for moderate pressures of $0.1$-$1.0$ GPa, depending on the composition, the electric polarization of bulk BFCO increases by $\sim 200$%. The origin of such an exceptional behavior is a phase transformation involving a low-$T$ rhombohedral (${\cal R}$) phase and a high-$T$ super-tetragonal (${\cal T}$) phase. Both ${\cal R}$ and ${\cal T}$ phases are ferrimagnetic near room temperature with an approximate net magnetization of $0.13$$\mu_{B}$ per formula unit. Contrarily to what occurs in either bulk BiFeO$_{3}$ or BiCoO$_{3}$, the ${\cal T}$ phase is stabilized over the ${\cal R}$ by increasing temperature due to its higher vibrational entropy. This extraordinary $T$-induced ${\cal R} \to {\cal T}$ phase transition is originated by polar phonon modes involving concerted displacements of transition-metal and oxygen ions.
- arXiv:2003.02961 [pdf, other]
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Title: Structure- and laser-gauges for the semiconductor Bloch equations in high-harmonic generation in solidsJournal-ref: Phys. Rev. A 101, 053411 (2020)Subjects: Atomic Physics (physics.atom-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Optics (physics.optics)
The semiconductor Bloch equations (SBEs) are routinely used for simulations of strong-field laser-matter interactions in condensed matter. In systems without inversion or time-reversal symmetries, the Berry connections and transition dipole phases (TDPs) must be included in the SBEs, which in turn requires the construction of a smooth and periodic structure gauge for the Bloch states. Here, we illustrate a general approach for such a structure-gauge construction for topologically trivial systems. Furthermore, we investigate the SBEs in the length and velocity gauges, and discuss their respective advantages and shortcomings for the high-harmonic generation (HHG) process. We find that in cases where we require dephasing or separation of the currents into interband and intraband contributions, the length gauge SBEs are computationally more efficient. In calculations without dephasing and where only the total current is needed, the velocity gauge SBEs are structure-gauge independent and are computationally more efficient. We employ two systems as numerical examples to highlight our findings: an 1D model of ZnO and the 2D monolayer hexagonal boron nitride (h-BN). The omittance of Berry connections or TDPs in the SBEs for h-BN results in nonphysical HHG spectra. The structure- and laser-gauge considerations in the current work are not restricted to the HHG process, and are applicable to all strong-field matter simulations with SBEs.
- arXiv:2003.02963 [pdf, ps, other]
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Title: A simple self-avoiding walking process as a reasonable non-conventional generator of polymeric linear chainsComments: The manuscript contains 17 pages and 12 figuresSubjects: Statistical Mechanics (cond-mat.stat-mech); Soft Condensed Matter (cond-mat.soft)
In this work, we present a simple and efficient generator of polymeric linear chains, based on a random self-avoiding walk process. The chains are generated using a discrete process of growth, in cubic networks and in a finite time, without border limits and without exploring all the configurational space. First, we thoroughly describe the chains morphology exploring the statistics of two characteristic distances, the radius of gyration and the end-to-end distance. Moreover, we examine the dependence of mean characteristic distances with the number of steps (N). Despite the simplicity of our procedure, we obtain universal critical exponents, which are in very good agreement with previous values reported in the literature. Moreover, studying the balance between the monomer-monomer interaction and the bending energy, we find that initially, the chains develop by multiple doubling, forming a cluster and increasing its energy. After reaching a given number of steps, the chains stretch and flee from the cluster, which results in a reduction of its interaction energy. However, the behaviour of the bending energy reveals that the chains follow the same folding pathway in both regimes. Additionally, we also characterize the energy of the obtained chains, combining the local interaction energy with its corresponding bending energy but in a discrete version. This analysis is relevant because it allows differentiating between chains of equal interaction energy but with different structures.
- arXiv:2003.02969 [pdf, other]
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Title: Lattice dynamics and polarization-dependent phonon damping in $α$-phase FeSi$_{2}$ nanoislandsAuthors: J. Kalt, M. Sternik, B. Krause, I. Sergueev, M. Mikolasek, D. Bessas, O. Sikora, T. Vitova, J. Göttlicher, R. Steininger, P. T. Jochym, A. Ptok, O. Leupold, H.-C. Wille, A. I. Chumakov, P. Piekarz, K. Parlinski, T. Baumbach, S. StankovComments: 13 pages, 9 figures, 3 tablesJournal-ref: Phys. Rev. B 101, 165406 (2020)Subjects: Materials Science (cond-mat.mtrl-sci); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We determined the lattice dynamics of metastable, surface-stabilized $\alpha$-phase FeSi$_2$ nanoislands epitaxially grown on the Si(111) surface with average heights and widths ranging from 1.5 to 20 nm and 18 to 72 nm, respectively. The crystallographic orientation, surface morphology and local crystal structure of the nanoislands were investigated by reflection high-energy electron diffraction, atomic force microscopy and X-ray absorption spectroscopy. The Fe-partial phonon density of states (PDOS), obtained by nuclear inelastic scattering, exhibits a pronounced damping and broadening of the spectral features with decreasing average island height. First-principles calculations of the polarization-projected Si- and Fe-partial phonon dispersions and PDOS enable the disentanglement of the contribution of the $xy$- and $z$-polarized phonons to the experimental PDOS. Modeling of the experimental data with the theoretical results unveils an enhanced damping of the $z$-polarized phonons for islands with average sizes below 10 nm. This phenomenon is attributed to the fact that the low-energy $z$-polarized phonons couple to the low-energy surface/interface vibrational modes. The thermodynamic and elastic properties obtained from the experimental data show a pronounced size-dependent behavior.
- arXiv:2003.02975 [pdf, other]
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Title: Evidence that LVV Auger transitions in oxygen can result in low-energy electron emissionSubjects: Materials Science (cond-mat.mtrl-sci)
In this paper, we present evidence of low-energy electron emission resulting from the LVV Auger decay of oxygen 2s holes. Low-energy Auger electron emission is difficult to observe principally because of the large, primary beam-induced secondary electron beam. We have overcome this background limitation by using positron-electron annihilation to initiate the Auger process. We present time-of-flight positron annihilation-induced Auger electron spectroscopy measurements of Cu, Si and TiO$_{2}$ surfaces using positrons with kinetic energies less than 1.5 eV. These experiments demonstrate that the majority of spectral weight in the annihilation-induced Auger electron spectra in the energy range of 0-15 eV is associated with the presence of oxygen at the surface. Using an empirically derived lineshape model that takes into account final state effects and the oxygen 2s photoemission line width, we argue that the low-energy intensity is consistent with the Auger decay of annihilation-induced 2s holes in oxygen (O LVV). In addition, we have calculated theoretically the electron kinetic energy distribution of O LVV Auger electrons emitted from a TiO$_{2}$(110) surface. The calculated lineshape is in excellent agreement with our experimental results. Finally, using the measured Auger intensities and the calculated O LVV lineshape, we estimate that the positron annihilation probability for O 2s electrons on a TiO$_2$ surface is 5.86%.
- arXiv:2003.02980 [pdf, other]
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Title: Spectral broadening of optical transitions at tunneling resonances in InAs/GaAs coupled quantum dot pairsAuthors: P. Kumar (1), C. Jennings (1), M. Scheibner (1), A. S. Bracker (2), S. G. Carter (2), D. Gammon (2) ((1) University of California Merced, (2) Naval Research Laboratory)Comments: 10 pages, 6 figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We report on linewidth analysis of optical transitions in InAs/GaAs coupled quantum dots as a function of bias voltage, temperature, and tunnel coupling strength. A significant line broadening up to 100 $\mu$eV is observed at hole tunneling resonances where the coherent tunnel coupling between spatially direct and indirect exciton states is maximized, corresponding to a phonon-assisted transition rate of 150 ns${}^{-1}$ at 20 K. With increasing temperature, the linewidth shows broadening characteristic of single-phonon transitions. The linewidth as a function of tunnel coupling strength tracks the theoretical prediction of linewidth broadening due to phonon-assisted transitions, and is maximized with an energy splitting between the two exciton branches of 0.8$-$0.9 meV. This report highlights the linewidth broadening mechanisms and fundamental aspects of the interaction between these systems and the local environment.
- arXiv:2003.02984 [pdf, ps, other]
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Title: Emergence of an upper bound to the electric field controlled Rashba spin splitting in InAs nanowiresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci)
The experimental assessment of the strength ($\alpha_R$) of the Rashba spin-orbit coupling is rather indirect and involves the measurement of the spin relaxation length from magnetotransport, together with a model of weak antilocalization. The analysis of the spin relaxation length in nanowires, however, clouds the experimental assessment of the $\alpha_R$ and leads to the prevailing belief that it can be tuned freely with electric field--a central tenant of spintronics. Here, we report direct theory of $\alpha_R$ leading to atomistic calculations of the spin band structure of InAs nanowires upon application of electric field-- a direct method that does not require a theory of spin relaxation. Surprisingly, we find an {\it upper bound} to the electric field tunable Rashba spin splitting and the ensuing $\alpha_R$; for InAs nanowires, $\alpha_R$ is pinned at about 170 meV{\AA} irrespective of the applied field strength. We find that this pinning is due to the quantum confined stark effect, that reduces continuously the nanowire band gap with applied electric field, leading eventually to band gap closure and a considerable increase in the density of free carriers. This results in turn in a strong screening that prevents the applied electric field inside the nanowire from increasing further beyond around 200 kV/cm for InAs nanowires. Therefore, further increase in the gate voltage will not increase $\alpha_R$. This finding clarifies the physical trends to be expected in nanowire Rashba SOC and the roles played by the nano size and electric field.
- arXiv:2003.02989 [pdf, other]
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Title: TensorFlow Quantum: A Software Framework for Quantum Machine LearningAuthors: Michael Broughton, Guillaume Verdon, Trevor McCourt, Antonio J. Martinez, Jae Hyeon Yoo, Sergei V. Isakov, Philip Massey, Murphy Yuezhen Niu, Ramin Halavati, Evan Peters, Martin Leib, Andrea Skolik, Michael Streif, David Von Dollen, Jarrod R. McClean, Sergio Boixo, Dave Bacon, Alan K. Ho, Hartmut Neven, Masoud MohseniComments: 39 pages, 24 figuresSubjects: Quantum Physics (quant-ph); Disordered Systems and Neural Networks (cond-mat.dis-nn); Machine Learning (cs.LG); Programming Languages (cs.PL)
We introduce TensorFlow Quantum (TFQ), an open source library for the rapid prototyping of hybrid quantum-classical models for classical or quantum data. This framework offers high-level abstractions for the design and training of both discriminative and generative quantum models under TensorFlow and supports high-performance quantum circuit simulators. We provide an overview of the software architecture and building blocks through several examples and review the theory of hybrid quantum-classical neural networks. We illustrate TFQ functionalities via several basic applications including supervised learning for quantum classification, quantum control, and quantum approximate optimization. Moreover, we demonstrate how one can apply TFQ to tackle advanced quantum learning tasks including meta-learning, Hamiltonian learning, and sampling thermal states. We hope this framework provides the necessary tools for the quantum computing and machine learning research communities to explore models of both natural and artificial quantum systems, and ultimately discover new quantum algorithms which could potentially yield a quantum advantage.
- arXiv:2003.02997 [pdf, other]
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Title: Bardasis-Schrieffer polaritons in excitonic insulatorsComments: 5 pages, 4 figuresSubjects: Strongly Correlated Electrons (cond-mat.str-el); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Superconductivity (cond-mat.supr-con)
Bardasis-Schrieffer modes in superconductors are fluctuations in subdominant pairing channels, e.g., d-wave fluctuations in an s-wave superconductor. This paper generalizes the notion to excitonic insulators and shows that these modes generically occur. In s-wave excitonic insulators, a p-wave Bardasis-Schrieffer mode exists below the gap energy and has a non-vanishing optical matrix element with light. This mode hybridizes strongly with photons to form Bardasis-Schrieffer polaritons, which are observable in both far-field and near-field optical experiments.
- arXiv:2003.03008 [pdf]
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Title: Assembly and disorder dissipation in superparamagnetic nanoparticle chains in a rotating magnetic fieldComments: 21 pages, 10 figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Soft Condensed Matter (cond-mat.soft)
We investigate the formation of chains of superparamagnetic iron oxide nanoparticles (SPIONs) in a rotating magnetic field. At present, this is a poorly explored regime that offers a way to study self-assembly away from thermal equilibrium in a relatively simple system that is prone to developing disorder through kinetic trapping. We find that the chain length distribution retains the exponential form seen in SPION chains assembled in a static magnetic field, and that the maximum chain length scales as the inverse of the square root of the magnetic field's frequency of oscillation, as is seen in chains formed in a rotating magnetic field from much larger magnetic beads. However, the chains are shorter than predicted by theories developed for either limit. We also characterize the disorder of the SPION chains, and find that it gradually dissipates over a timescale of tens of minutes, four orders of magnitude slower than the characteristic particle assembly time in the system. The disorder dissipation can be sped up by increasing particle concentration and solution ionic strength. We tentatively ascribe the disorder reduction to the continual churn of chains growing and fragmenting during the assembly, even after a steady state length distribution has obtained. This process may provide the energy required to free chains from kinetic traps too deep to be overcome through thermal fluctuations, promoting the gradual ordering of disordered chains as the suspension is allowed to evolve.
- arXiv:2003.03017 [pdf, other]
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Title: Membranes for spontaneous separation of pedestrian counter flowsComments: Manuscript accepted for publication in Europhysics LettersJournal-ref: Europhysics Letters 129 (5), 50005 (2020)Subjects: Physics and Society (physics.soc-ph); Soft Condensed Matter (cond-mat.soft); Adaptation and Self-Organizing Systems (nlin.AO)
Designing efficient traffic lanes for pedestrians is a critical aspect of urban planning as walking remains the most common form of mobility among the increasingly diverse methods of transportation. Herein, we investigate pedestrian counter flows in a straight corridor, in which two groups of people are walking in opposite directions. We demonstrate, using a molecular dynamics approach applying the social force model, that a simple array of obstacles improves flow rates by producing flow separations even in crowded situations. We also report on a developed model describing the separation behavior that regards an array of obstacles as a membrane and induces spontaneous separation of pedestrians groups. When appropriately designed, those obstacles are fully capable of controlling the filtering direction so that pedestrians tend to keep moving to their left (or right) spontaneously. These results have the potential to provide useful guidelines for industrial designs aimed at improving ubiquitous human mobility.
- arXiv:2003.03020 [pdf]
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Title: First-Principles Experimental Demonstration of Ferroelectricity in a Thermotropic Nematic Liquid Crystal: Spontaneous Polar Domains and Striking Electro-OpticsAuthors: Xi Chen, Eva Korblova, Dengpan Dong, Xiaoyu Wei, Renfan Shao, Leo Radzihovsky, Matthew Glaser, Joseph Maclennan, Dmitry Bedrov, David Walba, Noel ClarkComments: main paper: 23 pages; SI 34 pagesSubjects: Soft Condensed Matter (cond-mat.soft)
We report the experimental determination of the structure and response to applied electric field of the lower-temperature nematic phase of the previously reported calamitic compound 4-[(4-nitrophenoxy)carbonyl]phenyl2,4-dimethoxybenzoate (RM734). We exploit its electro-optics to visualize the appearance, in the absence of applied field, of a permanent electric polarization density, manifested as a spontaneously broken symmetry in distinct domains of opposite polar orientation. Polarization reversal is mediated by field-induced domain wall movement, making this phase ferroelectric, a 3D uniaxial nematic having a spontaneous, reorientable, polarization locally parallel to the director. This polarization density saturates at a low temperature value of ~ 6 microcoulombs/cm-sqd, the largest ever measured for an organic material or for any fluid. This polarization is comparable to that of solid state ferroelectrics, and is close to the average value obtained by assuming perfect, polar alignment of molecular long axes in the nematic. We find a host of spectacular optical and hydrodynamic effects driven by ultra-low applied field (E~1V/cm), produced by the coupling of the large polarization to nematic birefringence and flow. Electrostatic self-interaction of the polarization charge renders the transition from the nematic phase mean-field-like and weakly first-order, and controls the director field structure of the ferroelectric phase. Atomistic molecular dynamics simulation reveals short-range polar molecular interactions that favor ferroelectric ordering, including a tendency for head-to-tail association into polar, chain-like assemblies having polar lateral correlations. These results indicate a significant potential for transformative new nematic science and technology based on the enhanced understanding, development, and exploitation of molecular electrostatic interaction.
- arXiv:2003.03023 [pdf, other]
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Title: A realistic non-local heat engine based on Coulomb coupled systemsAuthors: Aniket SinghaComments: 19 Pages, 11 FiguresSubjects: Applied Physics (physics.app-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Optimal non-local heat-engines, based on Coulomb-coupled systems, demand a sharp step-like change in the energy resolved system-to-reservoir coupling around the ground state of quantum-dots. Such a sharp step-like transition in the system-to-reservoir coupling cannot be achieved in a realistic scenario. Here, I propose realistic design for non-local heat engine based on Coulomb-coupled system, which circumvents the need for any change in the system-to-reservoir coupling, demanded by the optimal set-ups discussed in literature. I demonstrate that an intentionally introduced asymmetry (or energy difference) in the ground state configuration between adjacent tunnel coupled quantum dots, in conjugation with Coulomb coupling, is sufficient to convert the stochastic fluctuations from a non-local heat source into a directed flow of thermoelectric current. The performance, along with the regime of operation, of the proposed heat engine is then theoretically investigated using quantum-master-equation (QME) approach. It is demonstrated that the theoretical maximum power output for the proposed set-up is limited to about $50\%$ of the optimal design. Despite a lower performance compared to the optimal set-up, the novelty of the proposed design lies in the conjunction of fabrication simplicity along with reasonable power output. At the end, the sequential transport processes leading to a performance deterioration of the proposed set-up are analyzed and a method to alleviate such transport processes is discussed. The set-up proposed in this paper can be used to design and fabricate high-performance non-local cryogenic heat engines.
- arXiv:2003.03031 [pdf, ps, other]
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Title: Epitaxial growth and orientation-dependent anomalous Hall effect of noncollinear antiferromagnetic Mn$_3$Ni$_{0.35}$Cu$_{0.65}$N filmsComments: The following article has been accepted by Journal of Applied PhysicsSubjects: Materials Science (cond-mat.mtrl-sci); Strongly Correlated Electrons (cond-mat.str-el)
We report the growth of noncollinear antiferromagnetic (AFM) Mn$_3$Ni$_{0.35}$Cu$_{0.65}$N films and the orientation-dependent anomalous Hall effect (AHE) of (001) and (111) films due to nonzero Berry curvature. We found that post-annealing at 500$^\circ$C can significantly improve the AHE signals, though using the appropriate post-annealing conditions is important. The AHE and magnetization loops show sharp flipping at the coercive field in (111) films, while (001) films are hard to saturate by a magnetic field. The anomalous Hall conductivity of (111) films is an order of magnitude larger than that of (001) films. The present results provide not only a better understanding of the AHE in Mn$_3X$N systems but also further opportunities to study the unique phenomena related to noncollinear AFM.
- arXiv:2003.03034 [pdf, other]
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Title: Degenerate p orbitals flat band model and realization in two-dimensional materialsComments: 5 pages, 4 figuresSubjects: Materials Science (cond-mat.mtrl-sci); Other Condensed Matter (cond-mat.other)
We propose a flat band model based on degenerate $p$ orbitals at the centers of octahedrons which are closely-packed in a two-demensional structure. Our theoretical analysis and first-principles calculations show that the proposed flat band can be realized in 1T layered materials of alkali-metal chalogenides and metal-carbon group compounds. Some of the former are theoretically predicted to be stable as layered materials here (e.g. K$_2$S), and some of the latter have been experimentally fabricated in previous works (e.g. Gd$_2$CCl$_2$). More interestingly, our calculations show that the Gd$_2$CCl$_2$ monolayer prefers ferromagnetic order and harbors a spin polarized nearly flat band. Our theoretical model together with the material predictions provide a realistic platform for the realization of flat bands and related exotic quantum phases.
- arXiv:2003.03039 [pdf, other]
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Title: Critical non-Hermitian Skin EffectComments: 4+ pages of main text (including 4 figures), plus 6 pages of Supplementary Material (including 7 figures)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Quantum Physics (quant-ph)
This work uncovers a new class of criticality where eigenenergies and eigenstates of non-Hermitian lattice systems jump discontinuously across a critical point in the thermodynamic limit, unlike established Hermitian and non-Hermitian critical scenarios where spectrum remains continuous across a transition. Such critical behavior, dubbed the "critical skin effect", is rather generic, occuring whenever subsystems with dissimilar non-Hermitian skin localization lengths are coupled, however weakly. Due to the existence of this criticality, the thermodynamic limit and the zero-coupling limit cannot be exchanged, thus challenging the celebrated generalized Brillouin zone (GBZ) approach when applied to finite-size systems. As manifestations of the critical skin effect in finite-size systems, we present stimulating examples with anomalous scaling behavior regarding spectrum, correlation functions, entanglement entropy, and scale-free wavefunctions that decay exponentially rather than power-law. More spectacularly, topological in-gap modes can even be induced by changing the system size.
- arXiv:2003.03046 [pdf, other]
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Title: Imaging the Holon String by Quantum InterferenceAuthors: Tin-Lun HoComments: 5 pages, 3 figuresSubjects: Quantum Gases (cond-mat.quant-gas)
It has been a long sought goal of Quantum Simulation to find answers to long standing questions in condensed matter physics. A famous example is the ground and the excitations of 2D Hubbard model with strong repulsion below half filling. The system is a doped antiferromagnet. It is of great interests because of its possible relation to high Tc superconductor. Theoretically, the fermion excitations of this model are believed to split up into holons and spinions, and a moving holon is believed to leave behind it a string of "wrong" spins that mismatch with the antiferromagnet background. Here, we show that the properties of the ground state wavefunction and the holon excitation of the 2D Hubbard model can be revealed in unprecedented detail using the technique of quantum interference in atomic physics. This is achieved by using quantum interference to measure the Marshall sign of the doped antiferromanget. The region of wrong Marshall sign directly reflects the spatial extent of fluctuating string attached to the holon.
- arXiv:2003.03050 [pdf, other]
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Title: Dynamical Phase Transitions in a 2D Classical Nonequilibrium Model via 2D Tensor NetworksComments: 5 pages, 5 figuresSubjects: Statistical Mechanics (cond-mat.stat-mech)
We demonstrate the power of 2D tensor networks for obtaining large deviation functions of dynamical observables in a classical nonequilibrium setting. Using these methods, we analyze the previously unstudied dynamical phase behavior of the fully 2D asymmetric simple exclusion process with biases in both the x and y directions. We identify a dynamical phase transition, from a jammed to a flowing phase, and characterize the phases and the transition, with an estimate of the critical point and exponents.
- arXiv:2003.03054 [pdf, other]
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Title: Hexagonal boron nitride as an ideal substrate for carbon nanotube photonicsComments: 7 pages, 5 figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Hexagonal boron nitride is widely used as a substrate for two-dimensional materials in both electronic and photonic devices. Here, we demonstrate that two-dimensional hexagonal boron nitride is also an ideal substrate for one-dimensional single-walled carbon nanotubes. Nanotubes directly attached to hexagonal boron nitride show bright photoluminescence with narrow linewidth at room temperature, comparable to air-suspended nanotubes. Using photoluminescence excitation spectroscopy, we unambiguously assign the chiralities of nanotubes on boron nitride by tracking individual tubes before and after contact with boron nitride. Although hexagonal boron nitride has a low dielectric constant and is attached to only one side of the nanotubes, we observe that optical transition energies are redshifted as much as ~50 meV from the air-suspended nanotubes. We also perform statistical measurements on more than 400 tubes, and the redshifts are found to be dependent on tube diameter. This work opens up new possibilities for all-solid-state carbon nanotube photonic devices by utilizing hexagonal boron nitride substrates.
- arXiv:2003.03057 [pdf, other]
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Title: Tuning the stability of Electrochemical Interfaces by Electron Transfer reactionsComments: 10 pages, 6 figuresSubjects: Chemical Physics (physics.chem-ph); Materials Science (cond-mat.mtrl-sci)
The morphology of interfaces is known to play fundamental role on the efficiency of energy-related applications, such light harvesting or ion intercalation. Altering the morphology on demand, however, is a very difficult task. Here, we show ways the morphology of interfaces can be tuned by driven electron transfer reactions. By using non-equilibrium thermodynamic stability theory, we uncover the operating conditions that alter the interfacial morphology. We apply the theory to ion intercalation and surface growth where electrochemical reactions are described using Butler-Volmer or coupled ion-electron transfer kinetics. The latter connects microscopic/quantum mechanical concepts with the morphology of electrochemical interfaces. Finally, we construct non-equilibrium phase diagrams in terms of the applied driving force (current/voltage) and discuss the importance of engineering the density of states of the electron donor in applications related to energy harvesting and storage, electrocatalysis and photocatalysis.
- arXiv:2003.03088 [pdf]
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Title: Electron-Doping Effect on Tc in the Undoped (Ce-Free) Superconductor T'-La1.8Eu0.2CuO4 Studied by the Fluorine Substitution for OxygenAuthors: Toshiki Sunohara, Takayuki Kawamata, Kota Shiosaka, Tomohisa Takamatsu, Takashi Noji, Masatsune Kato, Yoji KoikeComments: 14 pages, 5 figuresJournal-ref: Journal of the Physical Society of Japan 89, 014701 (2020)Subjects: Superconductivity (cond-mat.supr-con)
We have succeeded in synthesizing electron-doped polycrystalline bulk samples of T'-La1.8Eu0.2CuO4-yFy (y = 0 - 0.15) by the fluorination of undoped (Ce-free) T'-La1.8Eu0.2CuO4 using NH4F. The magnetic susceptibility measurements have revealed that the superconducting transition temperature, Tc, increases with increasing y, exhibits the maximum of 23 K at y = 0.025, and decreases. The dome-like dependence of Tc on the doped carrier concentration in the T'-type (La,Eu)-based cuprates is explained in terms of the pairing mediated by spin fluctuations based on the d-p model calculation [K. Yamazaki et al., J. Phys.: Conf. Ser. 871, 012009 (2017)].
- arXiv:2003.03096 [pdf, other]
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Title: Experimental realization of diffusion with stochastic resettingComments: 6 pages 5 figuresSubjects: Statistical Mechanics (cond-mat.stat-mech); Soft Condensed Matter (cond-mat.soft); Optics (physics.optics)
Stochastic resetting is prevalent in natural and man-made systems giving rise to a long series of non-equilibrium phenomena. Diffusion with stochastic resetting serves as a paradigmatic model to study these phenomena, but the lack of a well-controlled platform by which this process can be studied experimentally has been a major impediment to research in the field. Here, we report the experimental realization of colloidal particle diffusion and resetting via holographic optical tweezers. This setup serves as a proof-of-concept which opens the door to experimental study of resetting phenomena. It also vividly illustrates why existing theoretical models must be improved and revised to better capture the real-world physics of stochastic resetting.
- arXiv:2003.03102 [pdf, other]
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Title: g-tensor resonance in double quantum dots with site-dependent g-tensorsComments: 11 pages, 4 figures, 1 tableSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Quantum Physics (quant-ph)
Pauli spin blockade (PSB) has long been an important tool for spin read-out in double quantum dot (DQD) systems with interdot tunneling $t$. In this paper we show that the blockade is lifted if the two dots experience distinct effective magnetic fields caused by site-dependent g-tensors $g_L$ and $g_R$ for the left and right dot, and that this effect can be more pronounced than the leakage current due to the spin-orbit interaction (SOI) via spin-flip tunneling and the hyperfine interaction (HFI) of the electron spin with the host nuclear spins. Using analytical results obtained in special parameter regimes, we show that information about both the out-of-plane and in-plane g-factors of the dots can be inferred from characteristic features of the magneto-transport curve. For a symmetric DQD, we predict a pronounced maximum in the leakage current at the characteristic out-of-plane magnetic field $B^* = t/ \mu_B \sqrt{g_z^L g_z^R}$ which we term the g-tensor resonance of the system. Moreover, we extend the results to contain the effects of strong SOI and argue that in this more general case the leakage current carries information about the g-tensor components and SOI of the system.
- arXiv:2003.03103 [pdf, ps, other]
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Title: Dynamics of Hard Colloidal Cuboids in Nematic Liquid CrystalsComments: 8 pages, 7 figuresJournal-ref: Phys. Rev. E 101, 052702 (2020)Subjects: Soft Condensed Matter (cond-mat.soft)
We perform Dynamic Monte Carlo simulations to investigate the equilibrium dynamics of hard colloidal cuboids in oblate and prolate nematic liquid crystals. In particular, we characterise the particles' diffusion along the nematic director and perpendicularly to it, and observe a structural relaxation decay that strongly depend on the particle anisotropy. To assess the Gaussianity of their dynamics and eventual occurrence of collective motion, we calculate two- and four-point correlation functions that incorporate the instantaneous values of the diffusion coefficients parallel and perpendicular to the nematic director. Our simulation results highlight the occurrence of Fickian and Gaussian dynamics at short and long times, locate the minimum diffusivity at the self-dual shape, the particle geometry that would preferentially stabilise biaxial nematics, and exclude the existence of dynamically correlated particles.
- arXiv:2003.03111 [pdf]
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Title: Universal Behaviour of Settling and spreading of particle clusters in quiescent fluids in confined vesselsSubjects: Fluid Dynamics (physics.flu-dyn); Soft Condensed Matter (cond-mat.soft)
Here we report experiments on particle cluster settling at high Reynolds number in quiescent fluid contained in a vessel. The particles were observed to settle in a near-circular shape irrespective of the shape of the vessel cross-section and particle shape, size, and types. Effect of different parameters such as mass, type and aspect ratio of the particles, height, and viscosity of liquid was investigated. Formation of the hemispherical bottom cap of the cluster that bounces upon hitting the vessel bottom surface was found to be responsible for the final circular shape of the settled structure. Particle leakage from the cluster was seen in the form of a tail. In the liquid having viscosity beyond 100 cP, cluster breakage was observed that resulted in hindered settling and asymmetric shapes of finally settled particles. The observations are useful to understand the overall area over which settling of such clusters can be observed.
- arXiv:2003.03112 [pdf, other]
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Title: Bounds on the entanglement entropy by the number entropy in non-interacting fermionic systemsAuthors: Maximilian Kiefer-Emmanouilidis (1 and 2), Razmik Unanyan (1), Jesko Sirker (2), Michael Fleischhauer (1) ((1) Department of Physics and Research Center OPTIMAS, University of Kaiserslautern, Kaiserslautern, Germany, (2) Department of Physics and Astronomy, University of Manitoba, Winnipeg, Canada)Subjects: Disordered Systems and Neural Networks (cond-mat.dis-nn); Quantum Gases (cond-mat.quant-gas); Statistical Mechanics (cond-mat.stat-mech); Strongly Correlated Electrons (cond-mat.str-el)
Entanglement in a pure state of a many-body system can be characterized by the R\'enyi entropies $S^{(\alpha)}=\ln\textrm{tr}(\rho^\alpha)/(1-\alpha)$ of the reduced density matrix $\rho$ of a subsystem. These entropies are, however, difficult to access experimentally and can typically be determined for small systems only. Here we show that for free fermionic systems in a Gaussian state and with particle number conservation, $\ln S^{(2)}$ can be tightly bound by the much easier accessible R\'enyi number entropy $S^{(2)}_N=-\ln \sum_n p^2(n)$ which is a function of the probability distribution $p(n)$ of the total particle number in the considered subsystem only. A dynamical growth in entanglement, in particular, is therefore always accompanied by a growth---albeit logarithmically slower---of the number entropy. We illustrate this relation by presenting numerical results for quenches in non-interacting one-dimensional lattice models including disorder-free, Anderson-localized, and critical systems with off-diagonal disorder.
- arXiv:2003.03115 [pdf, other]
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Title: Bulk self-assembly of giant, unilamellar vesiclesComments: 9 pages, 4 figuresSubjects: Soft Condensed Matter (cond-mat.soft)
The desire to create cell-like models for fundamental science and applications has spurred extensive effort towards creating giant unilamellar vesicles (GUVs). However, a route to selectively self-assemble GUVs in bulk has remained elusive. In bulk solution, membrane-forming molecules such as phospholipids, single-tailed surfactants, and block copolymers typically self-assemble into multilamellar, onion-like structures. So although self-assembly processes can form nanoscale unilamellar vesicles, scaffolding by droplets or surfaces is required to create GUVs. Here we show that surprisingly, it is possible to bulk self-assemble cell-sized GUVs with almost complete selectivity over other vesicle topologies. The seemingly paradoxical pair of features that enables this appears to be having very dynamic molecules at the nanoscale, that create unusually rigid membranes. The resultant self-assembly pathway enables encapsulation of molecules and colloids, and can also generate model primitive cells that can grow and divide
- arXiv:2003.03117 [pdf, other]
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Title: Superconducting properties of the hole-doped three-band \emph{d-p} model studied with minimal-size real-space \emph{d}-wave pairing operatorsSubjects: Superconductivity (cond-mat.supr-con); Strongly Correlated Electrons (cond-mat.str-el)
The three-band \emph{d-p} model is investigated by means of Variational Monte-Carlo (VMC) method with the BCS-like wave-function supplemented by the Gutzwiller and Jastrow correlators. The VMC optimization leads to $d$-$wave$ superconducting state with a characteristic dome-like shape of the order parameter for hole doping $\delta \lesssim 0.4$, in a good agreement with the experimental observations. Also, the off-diagonal pair-pair correlation functions, calculated within VMC, vindicates the results obtained very recently within the diagrammatic expansion of the Gutzwiller wave function method (DE-GWF) [cf. Phys. Rev. B \textbf{99}, 104511 (2019)]. Subsequently, the nature of the $d$-$wave$ pairing is investigated by means of recently proposed \emph{minimal-size real-space d-wave pairing operators} [Phys. Rev. B \textbf{100}, 214502 (2019)]. An emergence of the long-range superconducting ordering for both $d$ and $p$ orbitals is reported by analysing the corresponding off-diagonal pair-pair correlation functions. The dominant character of \emph{d-wave} pairing on $d$ orbitals is confirmed. Additionally, the trial wave-function is used to investigate the magnetic properties of the system. The analysis of spin-spin correlation functions is carried out and shows antiferromagnetic $\mathbf{q}=(\pi,\pi)$, short-range order, as expected. For the sake of completeness, the charge gap has been estimated, which for the parent compound takes the value $\Delta_{CG}\approx1.78\pm0.51\text{ eV}$, and agrees with values reported experimentally for the cuprates.
- arXiv:2003.03126 [pdf, ps, other]
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Title: Metastability in the Potts model: exact results in the large q limitComments: 29 pages, 8 figuresSubjects: Statistical Mechanics (cond-mat.stat-mech)
We study the metastable equilibrium properties of the Potts model with heat-bath transition rates using a novel expansion. The method is especially powerful for large number of state spin variables and it is notably accurate in a rather wide range of temperatures around the phase transition.
- arXiv:2003.03130 [pdf, other]
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Title: A hyperelastic model for simulating cells in flowAuthors: Sebastian J. Müller (1), Franziska Weigl (2), Carina Bezold (1), Christian Bächer (1), Krystyna Albrecht (2), Stephan Gekle (1) ((1) Theoretical Physics VI, Biofluid Simulation and Modeling, University of Bayreuth, (2) Department of Functional Materials in Medicine and Dentistry and Bavarian Polymer Institute (BPI), University of Würzburg)Comments: submitted to Biomechanics and Modeling in Mechanobiology, 11 pages, 9 figures, Supplementary information includedSubjects: Biological Physics (physics.bio-ph); Soft Condensed Matter (cond-mat.soft); Fluid Dynamics (physics.flu-dyn)
In the emerging field of 3D bioprinting, cell damage due to large deformations is considered a main cause for cell death and loss of functionality inside the printed construct. Those deformations, in turn, strongly depend on the mechano-elastic response of the cell to the hydrodynamic stresses experienced during printing. In this work, we present a numerical model to simulate the deformation of biological cells in arbitrary three-dimensional flows. We consider cells as an elastic continuum according to the hyperelastic Mooney-Rivlin model. We then employ force calculations on a tetrahedralized volume mesh.
To validate our model, we perform a series of FluidFM(R) compression experiments with REF52 cells demonstrating that our hyperelastic model provides a very good description of the experimental data even at very large deformations up to 80%. In addition, we validate the model by comparing to axisymmetric simulations and to previous AFM experiments on bovine endothelial cells and artificial hydrogel particles. To investigate cell deformation in flow, we incorporate our model into Lattice Boltzmann simulations via an Immersed-Boundary algorithm. In linear shear flows, our model shows excellent agreement with analytical calculations and previous simulation data. - arXiv:2003.03146 [pdf, other]
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Title: Momentum-Dependent Mass and AC Hall Conductivity of Quantum Anomalous Hall Insulators and Their Relation to the Parity AnomalySubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); High Energy Physics - Theory (hep-th)
The Dirac mass of a two-dimensional QAH insulator is directly related to the parity anomaly of planar quantum electrodynamics, as shown initially in Phys. Rev. Lett. 52, 18 (1984). In this work, we connect the additional momentum-dependent Newtonian mass term of a QAH insulator to the parity anomaly. By calculating the effective action, we reveal that the Newtonian mass term acts like a parity-breaking element of a high-energy regularization scheme. As such, it is directly related to the parity anomaly. In addition, the calculation of the effective action allows us to determine the finite frequency correction to the DC Hall conductivity of a QAH insulator. We derive that the leading order AC correction contains a term proportional to the torsional Hall viscosity. This paves the way to measure this non-dissipative transport coefficient via electrical or magneto-optical experiments. Moreover, we prove that the Newtonian mass significantly changes the resonance structure of the AC Hall conductivity in comparison to pure Dirac systems like graphene.
- arXiv:2003.03156 [pdf, other]
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Title: Solvent-induced morphological transitions in methacrylate-based block-copolymer aggregatesSubjects: Soft Condensed Matter (cond-mat.soft)
Poly(ethylene oxide)-$\textit{b}$-poly(butylmethacrylate) (PEO-$\textit{b}$-PBMA) copolymers have recently been identified as excellent building blocks for the synthesis of hierarchical nanoporous materials. Nevertheless, while experiments have unveiled their potential to form bicontinuous phases and vesicles, a general picture of their phase and aggregation behavior is still missing. By performing Molecular Dynamics simulations, we here apply our recent coarse-grained model of PEO-$\textit{b}$-PBMA to investigate its self-assembly in water and tetrahydrofuran (THF) and unveil the occurrence of a wide spectrum of mesophases. In particular, we find that the morphological phase diagram of this ternary system incorporates bicontinuous and lamellar phases at high copolymer concentrations, and finite-size aggregates, such as dispersed sheets or disk-like aggregates, spherical vesicles and rod-like vesicles, at low copolymer concentrations. The morphology of these mesophases can be controlled by tuning the THF/water relative content, which has a striking effect on the kinetics of self-assembly as well as on the resulting equilibrium structures. Our results disclose the fascinating potential of PEO-$\textit{b}$-PBMA copolymers for the templated synthesis of nanostructured materials and offer a guideline to fine-tune their properties by accurately selecting the THF/water ratio.
- arXiv:2003.03159 [pdf, ps, other]
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Title: Radial Fulde-Ferrell-Larkin-Ovchinnikov state in a population-imbalanced Fermi gasComments: 7 pages, 4 figuresSubjects: Quantum Gases (cond-mat.quant-gas); Superconductivity (cond-mat.supr-con); Nuclear Theory (nucl-th)
The possibility of a Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state in a population imbalanced Fermi gas with a vortex is proposed. Employing the Bogoliubov-de-Gennes formalism we self-consistently determine the superfluid order parameter and the particle number density in the presence of a vortex. We find that as increasing population imbalance, the superfluid order parameter spatially oscillates around the vortex core in the radial direction, indicating that the FFLO state becomes stable. We find that the radial FFLO states cover a wide region of the phase diagram in the weak-coupling regime at $T=0$ in contrast to the conventional case without a vortex. We show that this inhomogeneous superfluidity can be detected as peak structures of the local polarization rate associated with the node structure of the superfluid order parameter. Since the vortex in the 3D Fermi gas with population imbalance has been already realized in experiments, our proposal is a promising candidate of the FFLO state in cold atom physics.
- arXiv:2003.03161 [pdf, other]
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Title: Indium tin oxide films meet circular Rydberg atoms: prospects for novel quantum simulation schemesAuthors: Florian Meinert, Christian Hölzl, Mehmet Ali Nebioglu, Alessandro D'Arnese, Philipp Karl, Martin Dressel, Marc SchefflerComments: 7 pages, 4 figuresJournal-ref: Phys. Rev. Research 2, 023192 (2020)Subjects: Atomic Physics (physics.atom-ph); Materials Science (cond-mat.mtrl-sci); Quantum Gases (cond-mat.quant-gas)
Long-lived circular Rydberg atoms are picking up increasing interest for boosting coherence times in Rydberg-based quantum simulation. We elaborate a novel approach to stabilize circular Rydberg states against spontaneous and blackbody-induced decay using a suppression capacitor made from indium tin oxide (ITO) thin films, which combine reflection of microwaves with transparency in the visible spectral range. To this end, we perform detailed characterization of such films using complementary spectroscopic methods at GHz and THz frequencies and identify conditions that allow for reaching circular-state lifetimes up to tens of milliseconds in a room-temperature environment. We discuss prospects of our findings in view of the quest for quantum simulations with high-$n$ circular Rydberg states at room temperature.
- arXiv:2003.03163 [pdf, other]
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Title: Dynamical Transitions of Supercooled Water in Graphene oxide Nanopores: Influence of Surface HydrophobicityComments: 16 pages, 8 figuresSubjects: Soft Condensed Matter (cond-mat.soft)
Molecular dynamics simulations are carried out to explore the dynamical crossover phenomenon in strongly confined and mildly supercooled water in graphene oxide nanopores. In contrast to studies where confinement is used to study the properties of bulk water, we are interested in the dynamical transitions for strongly confined water in the absence of any bulk-like water. The influence of the physicochemical nature of the graphene oxide surface on the dynamical transitions is investigated by varying the extent of hydrophobicity on the confining surfaces placed at an inter-surface separation of 10 \AA\,. All dynamical quantities show a typical slowing down as the temperature is lowered from 298 to 200 K; however, the nature of the transition is a distinct function of the surface type. Water confined between surfaces consisting of alternating hydrophilic and hydrophobic regions exhibit a strong-to-strong dynamical transition in the diffusion coefficients and rotational relaxation times at a crossover temperature of 237 K and show a fragile-to-strong transition in the $\alpha$-relaxation time at 238 K. The observed crossover temperature is much higher than the freezing point of the SPC/E water model used in this study, indicating that these dynamical transitions can occur with mild supercooling under strong confinement in the absence of bulk-like water. In contrast, water confined in hydrophilic pore shows a single Arrhenius energy barrier over the entire temperature range. Our results indicate that in addition to confinement, the nature of the surface can play a critical role in determining the dynamical transitions for water upon supercooling.
- arXiv:2003.03166 [pdf]
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Title: Unexpected band gap increase in the Fe2VAl Heusler compoundComments: 10 pages, 5 figuresJournal-ref: Materials Today Physics (2020)Subjects: Materials Science (cond-mat.mtrl-sci)
Knowing the electronic structure of a material is essential in energy applications to rationalize its performance and propose alternatives. Materials for thermoelectric applications are generally small-gap semiconductors and should have a high figure of merit ZT. Even if the Fe2VAl Heusler compound has a decent ZT, its conductive nature (semi-metal or semiconductor) is not yet clarified especially at low temperature. In this paper, we focus our DFT calculations on the effect of temperature on the bandgap of Fe2VAl. In contrast to what is usually observed, we show that both the temperature increase and the formation of thermally-activated Al/V inversion defects (observed experimentally), open the bandgap. Such an unusual behavior is the key for reconciling all bandgap measurements performed on the Fe2VAl compound using a standard GGA functional and could be an efficient way for improving the thermoelectric properties of this family of materials.
- arXiv:2003.03176 [pdf, other]
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Title: Beyond linear coupling in microwave optomechanicsAuthors: D. Cattiaux, X. Zhou, S. Kumar, I. Golokolenov, R. R. Gazizulin, A. Luck, L. Mercier de Lépinay, M. Sillanpää, A. D. Armour, A. Fefferman, E. CollinComments: 13 pages, submittedSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Quantum Physics (quant-ph)
We explore the nonlinear dynamics of a microwave optomechanical system consisting of a drumhead nano-electro-mechanical resonator (NEMS) capacitively coupled to a microwave cavity. Experiments are performed under a strong microwave Stokes pumping which triggers mechanical self-sustained oscillations. We analyze the results in the framework of an extended nonlinear optomechanical theory, and demonstrate that quadratic and cubic coupling terms in the opto-mechanical Hamiltonian have to be considered. Quantitative agreement with the measurements is obtained considering only genuine geometrical nonlinearities: no thermo-optical instabilities are observed, in contrast with laser-driven systems. Based on these results, we describe a method to quantify nonlinear properties of microwave optomechanical systems. This method is clearly a new technique available in the quantum electro-mechanics toolbox, where higher-order coupling terms are proposed as a new resource for specific quantum schemes like quantum non-demolition (QND) measurements. We also find that the motion imprints a wide comb of extremely narrow peaks in the microwave output field, which could also be exploited in specific microwave-based measurements, potentially limited only by the quantum noise of the optical {\it and} the mechanical fields for a ground-state cooled NEMS device.
- arXiv:2003.03189 [pdf, other]
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Title: Ab initio theory of graphene-iron(II) phthalocyanine hybrid systems as scalable molecular spintronicsComments: 8 pages, 4 figures, 2 tablesSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci)
Graphene - transition metal phthalocyanine (G-MPc) hybrid systems constitute promising platforms for densely-packed single-molecule magnets (SMMs). Here, we selected iron(II) phthalocyanine (FePc) and investigated its interaction with pristine and defective graphene layers employing density functional theory. Our calculations indicate that thorough proper dehydrogenation of the benzol rings in the FePc molecule its adsorption to graphene is thermodynamically favorable. In general, the presence of anchoring sites on the graphene layer, i.e. point defects, additionally facilitates the adsorption of FePc, allowing one to achieve high density of SMMs per unit area. Using the combination of group theory, ligand field splitting, and the calculated PBE0 Kohn-Sham eigenvalue spectrum, we resolved the electronic structure and predicted the spin states of both, the isolated FePc and G-FePc hybrid systems. Regardless of adsorption site and the number of removed hydrogen atoms from the benzol rings of FePc, the magnetic moment of the SMM remains unchanged with respect to free FePc. These results should mediate a successful synthesis of densely-packed G-MPc systems and may open up new avenue in designing scalable graphene - SMMs systems for spintronics applications.
- arXiv:2003.03205 [pdf, other]
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Title: Dark Exciton Preparation in a Quantum Dot by a Longitudinal Light Field Tuned to Higher Exciton StatesSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Several important proposals to use semiconductor quantum dots in quantum information technology rely on the control of the dark exciton ground states, such as dark exciton based qubits with a $\mu$s life time. In this paper, we present an efficient way to occupy the dark exciton ground state by a single short laser pulse. The scheme is based on an optical excitation with a longitudinal field component featured by, e.g., radially polarized beams or certain Laguerre-Gauss or Bessel beams. Utilizing this component, we show within a configuration interaction approach that high-energy exciton states composed of light-hole excitons and higher dark heavy-hole excitons can be addressed. When the higher exciton relaxes, a dark exciton in its ground state is created.
- arXiv:2003.03209 [pdf, other]
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Title: Statistical Thermodynamics of Dislocations in SolidsAuthors: J.S. LangerComments: arXiv admin note: substantial text overlap with arXiv:1810.00286Subjects: Materials Science (cond-mat.mtrl-sci)
This review is a simplified summary of the thermodynamic dislocation theory, with special emphasis on the role of an effective temperature. Materials scientists, for decades, have asserted that statistical thermodynamics is not applicable to dislocations. By use of simple, first-principles analyses and comparisons with experimental data, I argue that these scientists have been wrong, and that this venerable field urgently needs to be revitalized because of its wide-ranging fundamental and technological importance. In addition to describing recent progress in understanding strain hardening, yielding, shear banding, and the like, I argue that the thermodynamic dislocation theory can lead to a much needed, first-principles understanding of brittle and ductile fracture in crystalline solids.
- arXiv:2003.03224 [pdf, other]
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Title: Comparative Scanning Tunneling Microscopy Study on HexaboridesAuthors: S. Wirth, Sahana Rößler, Lin Jiao, M. Victoria Ale Crivillero, Priscila F. S. Rosa, Z. FiskComments: 8 pages, 10 figuresSubjects: Materials Science (cond-mat.mtrl-sci)
We compare STM investigations on two hexaboride compounds, SmB$_6$ and EuB$_6$, in an effort to provide a comprehensive picture of their surface structural properties. The latter is of particular importance for studying the nature of the surface states in SmB$_6$ by surface-sensitive tools. Beyond the often encountered atomically rough surface topographies of {\it in situ}, low-temperature cleaved samples, differently reconstructed as well as B-terminated and, more rarely, rare-earth terminated areas could be found. With all the different surface topographies observed on both hexaborides, a reliable assignment of the surface terminations can be brought forward.
- arXiv:2003.03226 [pdf, other]
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Title: Spin-accumulation induced magnetic texture in a metal-insulator bilayerComments: 11 pages, 5 figures, including appendicesSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We consider the influence of a spin accumulation in a normal metal on the magnetic statics and dynamics in an adjacent magnetic insulator. In particular, we focus on arbitary angles between the spin accumulation and the easy-axis of the magnetic insulator. Based on Landau-Lifshitz-Gilbert phenomenology supplemented with magnetoelectronic circuit theory, we find that the magnetic texture twists into a stable configuration that turns out to be described by a virtual, or image, domain wall configuration, i.e., a domain wall outside the ferromagnet. We show that even when the spin accumulation is perpendicular to the anisotropy axis, the magnetic texture develops a component parallel to the spin accumulation for sufficiently large spin bias. The emergence of this parallel component gives rise to threshold behavior in the spin Hall magnetoresistance and nonlocal magnon transport. This threshold can be used to design novel spintronic and magnonic devices that can be operated without external magnetic fields.
- arXiv:2003.03232 [pdf, ps, other]
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Title: The colon-pileAuthors: Alexei VazquezComments: 4 pages, 5 figuresSubjects: Populations and Evolution (q-bio.PE); Statistical Mechanics (cond-mat.stat-mech); Biological Physics (physics.bio-ph)
Bacteria populate the colon where they replicate and migrate in response to nutrient availability. Here I model the colon bacterial population as a sandpile model, the colon-pile. Sand addition mimics bacterial replication and grains toppling represents bacterial migration coupled to high population density. The numerical simulations reveal a behaviour similar to non-conservative sandpile models, approaching a critical state with system wide avalanches when the death rate becomes negligible. The critical exponents estimation indicates that the colon-pile belongs to a new universality class. This work suggest that the colon microbiome is in a self-organised critical state, where small perturbations can trigger large scale rearrangements, covering an area comparable to the system size and characterised by a 1/f noise spectra
- arXiv:2003.03243 [pdf, other]
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Title: Mixed topology ring states for Hall effect and orbital magnetism in skyrmions of Weyl semimetalsSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Skyrmion lattices as a novel type of chiral spin states are attracting increasing attention, owing to their peculiar properties stemming from real-space topological properties. At the same time, the properties of magnetic Weyl semimetals with complex $k$-space topology are moving into the focus of research in spintronics. We consider the Hall transport properties and orbital magnetism of skyrmion lattices imprinted in topological semimetals, by employing a minimal model of a 2D mixed Weyl semimetal which, as a function of the magnetization direction, exhibits two Chern insulator phases separated by a Weyl state for an an in-plane magnetization direction. We find that while the orbital magnetization is topologically robust and Hall transport properties are very sensitive to the details of the spin distribution in accordance to the behavior expected from the recently discovered chiral Hall effect[1], their behavior in the region of the Chern insulator gap is largely determined by the properties of the so-called mixed topology ring states, emerging in domain walls that separate the skyrmion core from the ferromagnetic background. In particular, we show that these localized ring states possess a given orbital chirality which reverses sign as a function of the skyrmion radius, thereby mediating a smooth switching dynamics of the orbital magnetization of the skyrmion lattice. We speculate that while the emergent ring states can possibly play a role in the physics of Majorana states, probing their properties experimentally can provide insights into the details of skyrmionic spin structures.
- arXiv:2003.03244 [pdf]
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Title: Polar Rectification Effect in Electro-Fatigued SrTiO3 Based JunctionsAuthors: Xueli Xu, Hui Zhang, Zhicheng Zhong, Ranran zhang, Lihua Yin, Yuping Sun, Haoliang Huang, Yalin Lu, Yi Lu, Chun Zhou, Zongwei Ma, Lei Shen, Junsong Wang, Jiandong Guo, Jirong Sun, Zhigao ShengSubjects: Applied Physics (physics.app-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci)
Rectifying semiconductor junctions are crucial to electronic devices. They convert alternating current into direct one by allowing unidirectional charge flows. In analogy to the current-flow rectification for itinerary electrons, here, a polar rectification that based on the localized oxygen vacancies (OVs) in a Ti/fatigued-SrTiO3 (fSTO) Schottky junction is first demonstrated. The fSTO with OVs is produced by an electro-degradation process. The different movability of localized OVs and itinerary electrons in the fSTO yield a unidirectional electric polarization at the interface of the junction under the coaction of external and built-in electric fields. Moreover, the fSTO displays a pre-ferroelectric state located between paraelectric and ferroelectric phases. The pre-ferroelectric state has three sub-states and can be easily driven into a ferroelectric state by external electric field. These observations open up opportunities for potential polar devices and may underpin many useful polar-triggered electronic phenomena.
- arXiv:2003.03257 [pdf]
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Title: Niobium disulphide (NbS$_2$)-based (heterogeneous) electrocatalysts for an efficient hydrogen evolution reactionAuthors: Leyla Najafi, Sebastiano Bellani, Reinier Oropesa-Nuñez, Beatriz Martín-García, Mirko Prato, Vlastimil Mazánek, Doriana Debellis, Simone Lauciello, Rosaria Brescia, Zdeněk Sofer, Francesco BonaccorsoJournal-ref: Journal of Materials Chemistry A, 2019, 7, 25593-25608Subjects: Chemical Physics (physics.chem-ph); Materials Science (cond-mat.mtrl-sci)
The design of efficient and cost-effective catalysts for the hydrogen evolution reaction (HER) is the key for molecular hydrogen (H2) production from electrochemical water splitting. Transition metal dichalcogenides (MX2), most notably group-6 MX2 (e.g., MoS2 and WS2), are appealing catalysts for the HER alternative to the best, but highly expensive, Pt-group elements. However, their HER activity is typically restricted to their edge sites rather than their basal plane. Furthermore, their semiconducting properties hinder an efficient electron transfer to the catalytic sites, which impedes a high rate of H2 production. Herein, we exploit liquid-phase exfoliation-produced metallic (1H, 2H and 3R) NbS2 nanoflakes, belonging to the class of metallic layered group-5 MX2, to overcome the abovementioned limitations. Both chemical treatment with hygroscopic Li salt and electrochemical in operando self-nanostructuring are exploited to improve the NbS2 nanoflake HER activity. The combination of NbS2 with other MX2, in our case MoSe2, also provides heterogeneous catalysts accelerating the HER kinetics of the individual counterparts. The designed NbS2-based catalysts exhibit an overpotential at a cathodic current of 10 mA cm-2 (n10) as low as 0.10 and 0.22 V vs. RHE in 0.5 M H2SO4 and 1 M KOH, respectively. In 0.5 M H2SO4, the HER activity of the NbS2-based catalysts is also superior to those of the Pt/C benchmark at current densities higher than 80 mA cm-2. Our work provides general guidelines for a scalable and cost-effective exploitation of NbS2, as well as the entire MX2 portfolio, for attaining a viable H2 production through electrochemical routes.
- arXiv:2003.03261 [pdf, other]
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Title: Integrable boundary conditions in the antiferromagnetic Potts modelComments: 32 pages; typos correctedSubjects: Mathematical Physics (math-ph); Statistical Mechanics (cond-mat.stat-mech); High Energy Physics - Theory (hep-th)
We present an exact mapping between the staggered six-vertex model and an integrable model constructed from the twisted affine $D_2^2$ Lie algebra. Using the known relations between the staggered six-vertex model and the antiferromagnetic Potts model, this mapping allows us to study the latter model using tools from integrability. We show that there is a simple interpretation of one of the known K-matrices of the $D_2^2$ model in terms of Temperley-Lieb algebra generators, and use this to present an integrable Hamiltonian that turns out to be in the same universality class as the antiferromagnetic Potts model with free boundary conditions. The intriguing degeneracies in the spectrum observed in related works (arXiv:nlin/0002050 and arXiv:1707.09260) are discussed.
- arXiv:2003.03266 [pdf]
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Title: Structure-transport correlation reveals anisotropic charge transport in coupled PbS nanocrystal superlatticesAuthors: Andre Maier, Dmitry Lapkin, Nastasia Mukharamova, Philipp Frech, Dameli Assalauova, Alexandr Ignatenko, Ruslan Khubbutdinov, Sergey Lazarev, Michael Sprung, Florian Laible, Ronny Loeffler, Nicolas Previdi, Thomas Guenkel, Monika Fleischer, Frank Schreiber, Ivan A. Vartanyants, Marcus ScheeleComments: 49 pages, 20 FiguresSubjects: Materials Science (cond-mat.mtrl-sci)
Semiconductive nanocrystals (NCs) can be self-assembled into ordered superlattices (SLs) to create artificial solids with emerging collective properties. Computational studies have predicted that properties such as electronic coupling or charge transport are determined not only by the individual NCs but also by the degree of their organization and structure. However, experimental proof for a correlation between structure and charge transport in NC SLs is still pending. Here, we perform X-ray nano-diffraction and apply Angular X-ray Cross-Correlation Analysis (AXCCA) to characterize the structures of coupled PbS NC SLs, which are directly correlated with the electronic properties of the same SL microdomains. We find strong evidence for the effect of SL crystallinity on charge transport and reveal anisotropic charge transport in highly ordered monocrystalline hexagonal close-packed PbS NC SLs, caused by the dominant effect of shortest interparticle distance. This implies that transport anisotropy should be a general feature of weakly coupled NC SLs.
- arXiv:2003.03276 [pdf, other]
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Title: Zero-energy quasiparticles in an interacting nanowire containing a topological Josephson junctionComments: 6 pagesSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Superconductivity (cond-mat.supr-con)
We study a Josephson junction in a Kitaev chain with particle-hole symmetric nearest neighbor interactions. When the phase difference across the junction is $\pi$, we show analytically that the full spectrum is fourfold degenerate up to corrections that vanish exponentially in the system size. The Majorana bound states at the ends of the chain are known to survive interactions. Our result proves that the same is true for the zero-energy quasiparticle localized at the junction. We further study finite size corrections numerically, and show how repulsive interactions lead to stronger end-to-end correlations than in a noninteracting system with the same bulk gap.
- arXiv:2003.03288 [pdf, other]
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Title: Electronic correlations, spectral and magnetic properties of ZrZn$_2$Subjects: Strongly Correlated Electrons (cond-mat.str-el)
We present results of a theoretical study of a prototypical weak ferromagnet ZrZn$_2$. We use the density-functional theory (DFT)+dynamical mean-field theory (DMFT) method to study the electronic and local magnetic properties. The obtained DFT+DMFT electronic self-energies are Fermi-liquid like, indicating a small effective mass enhancement of the Zr $4d$ states $m^*/m\sim 1.1 - 1.3$ accompanied by partly formed local moments within the electronic states of $t_{2g}$ symmetry. The effect of electronic interaction is shown to be essential for determining the correct topology of some of the Fermi surface sheets. To study in detail the pressure dependence of the Curie temperature $T_{\rm C}$ and corresponding pressure-induced quantum phase transition, we consider an effective single-band model, constructed using the Zr $4d$ contribution to the total density of states. The model is studied within static and dynamic mean-field theory, as well as spin-fermion approach. We show that the spin-fermion approach yields the temperature dependence of susceptibility at ambient pressure and the pressure dependence $T_{\rm C}(p)$, including the first-order quantum phase transition at $p\approx 1.7$~GPa, comparable well with the experimental data.
- arXiv:2003.03302 [pdf, other]
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Title: Time-dependent branching processes: a model of oscillating neuronal avalanchesSubjects: Disordered Systems and Neural Networks (cond-mat.dis-nn); Statistical Mechanics (cond-mat.stat-mech)
Recently, neuronal avalanches have been observed to display oscillations, a phenomenon regarded as the co-existence of a scale-free behaviour (the avalanches close to criticality) and scale-dependent dynamics (the oscillations). Ordinary continuous-time branching processes with constant extinction and branching rates are commonly used as models of neuronal activity, yet they lack any such time-dependence. In the present work, we extend a basic branching process by allowing the extinction rate to oscillate in time as a new model to describe cortical dynamics. By means of a perturbative field theory, we derive relevant observables in closed form. We support our findings by quantative comparison to numerics and qualitative comparison to available experimental results.
- arXiv:2003.03306 [pdf, other]
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Title: Rotating mixed $^3$He-$^4$He nanodropletsComments: 6 pages, 4 figures (plus Supplemental Material). Revised version with corrections+missing figureSubjects: Quantum Gases (cond-mat.quant-gas)
Mixed $^3$He-$^4$He droplets created by hydrodynamic instability of a cryogenic fluid-jet may acquire angular momentum during their passage through the nozzle of the experimental apparatus. These free-standing droplets cool down to very low temperatures undergoing isotopic segregation, developing a nearly pure $^3$He crust surrounding a very $^4$He-rich superfluid core. Here, the stability and appearance of rotating mixed helium droplets are investigated using Density Functional Theory for an isotopic composition that highlights, with some marked exceptions related to the existence of the superfluid inner core, the analogies with viscous rotating droplets.
- arXiv:2003.03309 [pdf, other]
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Title: Multiplex Recurrence NetworksJournal-ref: Physical Review E, 97, 012312, 2018Subjects: Data Analysis, Statistics and Probability (physics.data-an); Disordered Systems and Neural Networks (cond-mat.dis-nn); Chaotic Dynamics (nlin.CD)
We have introduced a novel multiplex recurrence network (MRN) approach by combining recurrence networks with the multiplex network approach in order to investigate multivariate time series. The potential use of this approach is demonstrated on coupled map lattices and a typical example from palaeobotany research. In both examples, topological changes in the multiplex recurrence networks allow for the detection of regime changes in their dynamics. The method goes beyond classical interpretation of pollen records by considering the vegetation as a whole and using the intrinsic similarity in the dynamics of the different regional vegetation elements. We find that the different vegetation types behave more similar when one environmental factor acts as the dominant driving force.
- arXiv:2003.03312 [pdf, other]
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Title: Small Heterocyclic Molecule as Multistate Transistor: A Quantum Many-body ApproachSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci)
Weakly coupled molecular junctions are an active and important field of research as they exhibit various non-linear transport phenomena. We have investigated the carrier transport through weakly coupled B2C2N2H6 molecules using quantum many-body approach coupled with kinetic (master) equations. Interestingly, various types of non-linear current-voltage characteristics, such as, negative differential conductance (NDC), rectifications, Coulomb staircase, which is the hallmark of multistate transport devices, have been obtained. The source-drain voltage induced change in the occupation probabilities of low-lying many-body states which are different in nature towards carrier transport, directly control the net current flowing through the molecular junctions. We further investigate the effect of different kinds of perturbations such as gate voltage and perpendicular magnetic field, over carrier-flow through this molecular bridge. Interestingly, we find that depending on the strength of the applied perturbating field, several phenomena, such as switching off of current, suppression of NDC appears in the devices. Fundamentally, this applied perturbations modifies both the site charge density as well as occupation probabilities of transport active channels, resulting in a significant alteration in transport behavior of this molecular junction.
- arXiv:2003.03314 [pdf, other]
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Title: A superconducting nonlinear thermoelectric heat engineJournal-ref: Phys. Rev. B 101, 214509 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Superconductivity (cond-mat.supr-con)
In a previous work, we predicted that a thermally biased tunnel junction between two different superconductors can display a thermoelectric effect of nonlinear nature in the temperature gradient, under proper conditions. In this work we give a more extended discussion, and we focus on the two main features of the nonlinear contributions: i) the $linear-in-bias$ thermoelectricity, that can be associated to a spontaneous breaking of electron-hole symmetry, ii) the strong contribution at the matching peak singularity, which is typically associated to the maximum output power and efficiency. We discuss the nonlinear origin of the thermoelectricity and its relationship with the non-linear cooling mechanism in superconducting junctions previously discussed in the literature. Finally, we design and characterize the performance of the system as a heat engine, for a realistic design and experimental parameter values. We discuss possible non-idealities demonstrating that the system is amenable to current experimental realization.
- arXiv:2003.03319 [pdf, other]
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Title: Enhanced rotational motion of spherical squirmer in polymer solutionsComments: 5 figuresJournal-ref: Phys. Rev. Lett. 124, 068001 (2020)Subjects: Soft Condensed Matter (cond-mat.soft); Biological Physics (physics.bio-ph)
The rotational diffusive motion of a self-propelled, attractive spherical colloid immersed in a solution of self-avoiding polymers is studied by mesoscale hydrodynamic simulations. A drastic enhancement of the rotational diffusion by more than an order of magnitude in the presence of activity is obtained. The amplification is a consequence of two effects, a decrease of the amount of adsorbed polymers by active motion and an asymmetric encounter with polymers on the squirmer surface, which yields an additional torque and random noise for the rotational motion. Our simulations suggest a way to control the rotational dynamics of squirmer-type microswimmers by the degree of polymer adsorption and system heterogeneity.
- arXiv:2003.03321 [pdf]
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Title: Frustrated Magnetism in Triangular Lattice TlYbS$_2$ Crystals Grown via Molten FluxComments: 16 pages, 8 figuresJournal-ref: Front. Chem. 2020. 8:127Subjects: Materials Science (cond-mat.mtrl-sci); Strongly Correlated Electrons (cond-mat.str-el)
The triangular lattice compound TlYbS$_2$ was prepared as large single crystals via a molten flux growth technique using sodium chloride. Anisotropic magnetic susceptibility measurements down to 0.4 K indicate a complete absence of long-range magnetic order. Despite this lack of long-range order, short-range antiferromagnetic interactions are evidenced through broad transitions, suggesting frustrated behavior. Variable magnetic field measurements reveal metamagnetic behavior at temperatures less than 2 K. Complex low temperature field-tunable magnetic behavior, in addition to no observable long-range order down to 0.4 K, suggest that TlYbS$_2$ is a frustrated magnet and a possible quantum spin liquid candidate.
- arXiv:2003.03322 [pdf, other]
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Title: Competing long-range interactions and spin vector chirality in spin-chainsComments: 5 pages, 5 FiguresSubjects: Strongly Correlated Electrons (cond-mat.str-el); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Studies of competing orders in 1D magnetic chains have attracted considerable attention in recent years, as the presence of long-range Heisenberg interactions is found to allow interesting quantum phase transitions. We investigate here the role of spin-orbit effects by considering spin-1/2 chains in the presence of both collinear and non-collinear long-range interactions. By employing exact diagonalization and density matrix renormalization group calculations we investigate the rich phase diagram of this system. We find transitions from collinear to transverse magnetic correlated order as the strength of the non-collinear coupling increases, accompanied by a jump in the vector spin chirality order parameter of the system. This shows that tuning long-range interactions allows control of the onset of sizable vector spin chirality in a system, which may be used to transmit information down the chain. We investigate the characteristic structure of the distinct phases and explore their possible physical implementation in different materials systems.
- arXiv:2003.03324 [pdf]
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Title: Anisotropy in AntiferromagnetsAuthors: K O'Grady, J Sinclair, K Elphick, R Carpenter, G Vallejo-Fernandez, M I J Probert, A HirohataComments: 20 pages, 11 figures, invited paperSubjects: Materials Science (cond-mat.mtrl-sci)
Due to the advent of antiferromagnetic (AF) spintronics there is a burgeoning interest in AF materials for a wide range of potential and actual applications. Generally, AFs are characterized via the ordering at the Neel temperature (TN) but, to have a stable AF configuration, it is necessary that the material have a sufficient level of anisotropy so as to maintain the orientation of the given magnetic state fixed in one direction. Unlike the case for ferromagnets there is little established data on the anisotropy of AFs and in particular its origins and those factors which control it. In this paper these factors are reviewed in the light of recent and established experimental data. Additionally, there is no recognized technique for the first principle determination of the anisotropy of an AF which can only be found indirectly via the exchange bias phenomenon. This technique is reviewed and in particular the implications for the nature of the anisotropy that is measured and its distribution. Finally, a strategy is proposed that would allow for the development of AF materials with controlled anisotropy for future applications.
- arXiv:2003.03328 [pdf, other]
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Title: Type-II topological metalsComments: 12 pages, 16 figuresJournal-ref: Front. Phys. 15(4), 43201 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci)
Topological metals (TMs) are a kind of special metallic materials, which feature nontrivial band crossings near the Fermi energy, giving rise to peculiar quasiparticle excitations. TMs can be classified based on the characteristics of these band crossings. For example, according to the dimensionality of the crossing, TMs can be classified into nodal-point, nodal-line, and nodal-surface metals. Another important property is the type of dispersion. According to degree of the tilt of the local dispersion around the crossing, we have type-I and type-II dispersions. This leads to significant distinctions in the physical properties of the materials, owing to their contrasting Fermi surface topologies. In this article, we briefly review the recent advances in this research direction, focusing on the concepts, the physical properties, and the material realizations of the type-II nodal-point and nodal-line TMs.
- arXiv:2003.03334 [pdf, other]
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Title: Finite-temperature transport in one-dimensional quantum lattice modelsComments: Review article (74 pages, 34 figures). Comments welcome. Version 2: Additional references, minor text modifications in Secs. I, III, IV, VISubjects: Strongly Correlated Electrons (cond-mat.str-el); Statistical Mechanics (cond-mat.stat-mech); Quantum Physics (quant-ph)
The last decade has witnessed an impressive progress in the theoretical understanding of transport properties of clean, one-dimensional quantum lattice systems. Many physically relevant models in one dimension are Bethe-ansatz integrable, including the anisotropic spin-1/2 Heisenberg (also called spin-1/2 XXZ chain) and the Fermi-Hubbard model. Nevertheless, practical computations of, for instance, correlation functions and transport coefficients pose hard problems from both the conceptual and technical point of view. Only due to recent progress in the theory of integrable systems on the one hand and due to the development of numerical methods on the other hand has it become possible to compute their finite temperature and nonequilibrium transport properties quantitatively. Most importantly, due to the discovery of a novel class of quasilocal conserved quantities, there is now a qualitative understanding of the origin of ballistic finite-temperature transport, and even diffusive or super-diffusive subleading corrections, in integrable lattice models. We shall review the current understanding of transport in one-dimensional lattice models, in particular, in the paradigmatic example of the spin-1/2 XXZ and Fermi-Hubbard models, and we elaborate on state-of-the-art theoretical methods, including both analytical and computational approaches. Among other novel techniques, we discuss matrix-product-states based simulation methods, dynamical typicality, and, in particular, generalized hydrodynamics. We will discuss the close and fruitful connection between theoretical models and recent experiments, with examples from both the realm of quantum magnets and ultracold quantum gases in optical lattices.
- arXiv:2003.03336 [pdf]
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Title: Raman spectroscopy of GaSe and InSe post-transition metal chalcogenides layersAuthors: Maciej R. Molas, Anastasia V. Tyurnina, Viktor Zólyomi, Anna K. Ott, Daniel J. Terry, Matthew J. Hamer, Celal Yelgel, Adam Babiński, Albert G. Nasibulin, Andrea C. Ferrari, Vladimir I. Fal'ko, Roman GorbachevComments: 6 pages, 5 figuresJournal-ref: Faraday Discussions 2020Subjects: Materials Science (cond-mat.mtrl-sci); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
III-VI post-transition metal chalcogenides (InSe and GaSe) are a new class of layered semiconductors, which feature a strong variation of size and type of their band gaps as a function of number of layers (N). Here, we investigate exfoliated layers of InSe and GaSe ranging from bulk crystals down to monolayer, encapsulated in hexagonal boron nitride, using Raman spectroscopy. We present the N-dependence of both intralayer vibrations within each atomic layer, as well as of the interlayer shear and layer breathing modes. A linear chain model can be used to describe the evolution of the peak positions as a function of N, consistent with first principles calculations.
- arXiv:2003.03348 [pdf, other]
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Title: Search for axion-like dark matter with ferromagnetsSubjects: High Energy Physics - Experiment (hep-ex); Other Condensed Matter (cond-mat.other); Instrumentation and Detectors (physics.ins-det)
Existence of dark matter indicates the presence of unknown fundamental laws of nature. Ultralight axion-like particles are well-motivated dark matter candidates, emerging naturally from theories of physics at ultrahigh energies. We report the results of a direct search for the electromagnetic interaction of axion-like dark matter in the mass range that spans three decades from 12 peV to 12 neV. The detection scheme is based on a modification of Maxwell's equations in the presence of axion-like dark matter, which mixes with a static magnetic field to produce an oscillating magnetic field. The experiment makes use of toroidal magnets with iron-nickel alloy ferromagnetic powder cores, which enhance the static magnetic field by a factor of 24. Using SQUIDs, we achieve a magnetic sensitivity of 150 $\text{aT}/\sqrt{\text{Hz}}$, at the level of the most sensitive magnetic field measurements demonstrated with any broadband sensor. We recorded 41 hours of data and improved the best limits on the magnitude of the axion-like dark matter electromagnetic coupling constant over part of our mass range, at 20 peV reaching $3.3 \times 10^{-11} \text{GeV}^{-1}$ (95\% confidence level). Our measurements are starting to explore the coupling strengths and masses of axion-like particles where mixing with photons could explain the anomalous transparency of the universe to TeV gamma-rays.
- arXiv:2003.03353 [pdf, other]
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Title: Reappraising the distribution of the number of edge crossings of graphs on a sphereComments: Corrected mistakes in equation 31. Added new figure (7). Added acknowledgements to J. W. Moon. Other minor changesSubjects: Discrete Mathematics (cs.DM); Statistical Mechanics (cond-mat.stat-mech); Social and Information Networks (cs.SI); Physics and Society (physics.soc-ph)
Many real transportation and mobility networks have their vertices placed on the surface of the Earth. In such embeddings, the edges laid on that surface may cross. In his pioneering research, Moon analyzed the distribution of the number of crossings on complete graphs and complete bipartite graphs whose vertices are located uniformly at random on the surface of a sphere assuming that vertex placements are independent from each other. Here we revise his derivation of that variance in the light of recent theoretical developments on the variance of crossings and computer simulations. We show that Moon's formulae are inaccurate in predicting the true variance and provide exact formulae.
- arXiv:2003.03362 [pdf, other]
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Title: Analysis of Magnetic Vortex Dissipation in Sn-Segregated Boundaries in Nb$_3$Sn SRF CavitiesAuthors: Jared Carlson, Alden Pack, Mark K. Transtrum, Jaeyel Lee, David N. Seidman, Danilo B. Liarte, Nathan Sitaraman, Alen Senanian, James P. Sethna, Tomas Arias, Sam PosenSubjects: Superconductivity (cond-mat.supr-con); Materials Science (cond-mat.mtrl-sci); Accelerator Physics (physics.acc-ph); Computational Physics (physics.comp-ph)
We study mechanisms of vortex nucleation in Nb$_3$Sn SRF cavities using a combination of experimental, theoretical, and computational methods. Scanning transmission electron microscopy (STEM) image and energy dispersive spectroscopy (EDS) of some Nb$_3$Sn cavities show Sn segregation at grain boundaries in Nb$_3$Sn with Sn concentration as high as $\sim$35 at.% and widths $\sim$3 nm in chemical composition. Using ab initio calculations, we estimate the effect excess tin has on the local superconducting properties of the material. We model Sn segregation as a lowering of the local critical temperature. We then use time-dependent Ginzburg-Landau theory to understand the role of segregation on magnetic vortex nucleation. Our simulations indicate that the grain boundaries act as both nucleation sites for vortex penetration and pinning sites for vortices after nucleation. Depending on the magnitude of the applied field, vortices may remain pinned in the grain boundary or penetrate the grain itself. We estimate the superconducting losses due to vortices filling grain boundaries and compare with observed performance degradation with higher magnetic fields. We estimate that the quality factor may decrease by an order of magnitude ($10^{10}$ to $10^9$) at typical operating fields if 0.03% of the grain boundaries actively nucleate vortices. We additionally estimate the volume that would need to be filled with vortices to match experimental observations of cavity heating.
Replacements
- arXiv:1709.10479 (replaced) [pdf, other]
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Title: Statistics of a simple transmission mode on a lossy chaotic backgroundAuthors: Dmitry V. SavinComments: 6 pages, 3 figures (published version: discussion expanded with new eqs.(11)-(12), layout changed, figures updated, typos fixed)Journal-ref: Phys. Rev. Research 2, 013246 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Mathematical Physics (math-ph); Nuclear Theory (nucl-th); Quantum Physics (quant-ph)
Scattering on a resonance state coupled to a complicated background is a typical problem for mesoscopic quantum many-body systems as well as for wave propagation in the presence of a complex environment. On average, such a simple mode acquires an effective damping, the so-called "spreading" width, due to mixing with the background states. Modeling the latter by random matrix theory and employing the strength function formalism, we derive the joint distribution of the reflection and total transmission at arbitrary absorption in the background. The distribution is found to possess a remarkable symmetry between its reflection and transmission sectors, which is controlled by the ratio of the spreading to escape width. This in turn results in a symmetry relation between the marginal densities, despite the absence of the flux conservation at finite absorption. As an application, we study the statistics of total losses in the system at arbitrary coupling to the background.
- arXiv:1810.03364 (replaced) [pdf]
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Title: Identifying substitutional oxygen as a prolific point defect in monolayer transition metal dichalcogenides with experiment and theoryAuthors: Sara Barja, Sivan Refaely-Abramson, Bruno Schuler, Diana Y. Qiu, Artem Pulkin, Sebastian Wickenburg, Hyejin Ryu, Miguel M. Ugeda, Christoph Kastl, Christopher Chen, Choongyu Hwang, Adam Schwartzberg, Shaul Aloni, Sung-Kwan Mo, D. Frank Ogletree, Michael F. Crommie, Oleg V. Yazyev, Steven G. Louie, Jeffrey B. Neaton, Alexander Weber-BargioniJournal-ref: Nat Commun 10, 3382 (2019)Subjects: Materials Science (cond-mat.mtrl-sci)
Chalcogen vacancies are considered to be the most abundant point defects in two-dimensional (2D) transition-metal dichalcogenide (TMD) semiconductors, and predicted to result in deep in-gap states (IGS). As a result, important features in the optical response of 2D-TMDs have typically been attributed to chalcogen vacancies, with indirect support from Transmission Electron Microscopy (TEM) and Scanning Tunneling Microscopy (STM) images. However, TEM imaging measurements do not provide direct access to the electronic structure of individual defects; and while Scanning Tunneling Spectroscopy (STS) is a direct probe of local electronic structure, the interpretation of the chemical nature of atomically-resolved STM images of point defects in 2D-TMDs can be ambiguous. As a result, the assignment of point defects as vacancies or substitutional atoms of different kinds in 2D-TMDs, and their influence on their electronic properties, has been inconsistent and lacks consensus. Here, we combine low-temperature non-contact atomic force microscopy (nc-AFM), STS, and state-of-the-art ab initio density functional theory (DFT) and GW calculations to determine both the structure and electronic properties of the most abundant individual chalcogen-site defects common to 2D-TMDs. Surprisingly, we observe no IGS for any of the chalcogen defects probed. Our results and analysis strongly suggest that the common chalcogen defects in our 2D-TMDs, prepared and measured in standard environments, are substitutional oxygen rather than vacancies.
- arXiv:1811.12379 (replaced) [pdf, other]
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Title: Evolution of magneto-crystalline anisotropies in Mn$_{1-x}$Fe$_x$Si and Mn$_{1-x}$Co$_x$Si as inferred from small-angle neutron scattering and bulk propertiesAuthors: J. Kindervater, T. Adams, A. Bauer, F. Haslbeck, A. Chacon, S. Mühlbauer, F. Jonietz, A. Neubauer, U. Gasser, G. Nagy, N. Martin, W. Häußler, R. Georgii, M. Garst, C. PfleidererJournal-ref: Phys. Rev. B 101, 104406 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el); Other Condensed Matter (cond-mat.other)
We report a comprehensive small-angle neutron scattering~(SANS) study of Mn$_{1-x}$Fe$_{x}$Si at zero magnetic field. To delineate changes of magneto-crystalline anisotropies (MCAs) from effects due to defects and disorder, we recorded complementary susceptibility and specific heat data, and investigated selected compositions of Mn$_{1-x}$Co$_{x}$Si. For all systems studied the transition temperature and magnetic phase diagrams evolve monotonically with composition consistent with literature. The SANS patterns of the magnetic order recorded under zero-field cooling display strong changes of the directions of the intensity maxima and smeared out intensity distributions as a function of composition. We show that cubic MCAs account for the complex evolution of the SANS patterns, where for increasing $x$ the character of the MCAs shifts from terms that are fourth-order to terms that are sixth order in spin--orbit coupling. The magnetic field dependence of the susceptibility and SANS establishes that the helix reorientation as a function of magnetic field for Fe- or Co-doped MnSi is dominated by pinning due to defects and disorder. The presence of thermodynamic anomalies of the specific heat at the phase boundaries of the skyrmion lattice phase in the doped samples and properties observed in Mn$_{1-x}$Co$_{x}$Si establishes that the pinning due to defects and disorder remains, however, weak and comparable to the field scale of the helix reorientation. The observation that MCAs, that are sixth order in spin-orbit coupling, play an important role for the spontaneous order in Mn$_{1-x}$Fe$_{x}$Si and Mn$_{1-x}$Co$_{x}$Si, offering a fresh perspective for a wide range of topics in cubic chiral magnets such as the generic magnetic phase diagram, the morphology of topological spin textures, the paramagnetic-to-helical transition, and quantum phase transitions.
- arXiv:1812.04392 (replaced) [pdf, ps, other]
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Title: Uniform Perpendicular and Parallel Staggered Susceptibility of Antiferromagnetic FilmsAuthors: Christoph Peter HofmannComments: 27 pages, 7 figures; some figures redrawn due to numerical artifacts in previous version, conclusions unalteredSubjects: Strongly Correlated Electrons (cond-mat.str-el); High Energy Physics - Lattice (hep-lat); High Energy Physics - Phenomenology (hep-ph)
We investigate the thermodynamic behavior of antiferromagnetic films in external magnetic fields oriented perpendicular to the staggered magnetization. Within the systematic effective Lagrangian framework we first calculate the two-point function and the dispersion relation for the two types of magnons up to one-loop order. This allows us to split the two-loop free energy density into a piece that originates from noninteracting dressed magnons, and a second piece that corresponds to the genuine magnon-magnon interaction. We then discuss the low-temperature series for various thermodynamic quantities, including the parallel staggered and uniform perpendicular susceptibilities, and analyze the role of the spin-wave interaction at finite temperature.
- arXiv:1812.11193 (replaced) [pdf, other]
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Title: Classification of translation invariant topological Pauli stabilizer codes for prime dimensional qudits on two-dimensional latticesAuthors: Jeongwan HaahComments: 18 pages, (v2) removed the need of Clifford QCA of v1 using recent resultsSubjects: Quantum Physics (quant-ph); Strongly Correlated Electrons (cond-mat.str-el); Mathematical Physics (math-ph)
We prove that on any two-dimensional lattice of qudits of a prime dimension, every translation invariant Pauli stabilizer group with local generators and with code distance being the linear system size, is decomposed by a local Clifford circuit of constant depth into a finite number of copies of the toric code (abelian discrete gauge theory) stabilizer group. This means that under local Clifford circuits the number of toric code copies is the complete invariant of topological Pauli stabilizer codes. Previously, the same conclusion was obtained under the assumption of nonchirality for qubit codes or the Calderbank-Shor-Steane structure for prime qudit codes; we do not assume any of these.
- arXiv:1904.11324 (replaced) [pdf, other]
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Title: Scaling in the massive antiferromagnetic XXZ spin-1/2 chain near the isotropic pointAuthors: S. B. RutkevichComments: v3: 14 pages, 5 figures, extended version, two appendices addedJournal-ref: Phys. Rev. E 101, 032115 (2020)Subjects: Statistical Mechanics (cond-mat.stat-mech); Strongly Correlated Electrons (cond-mat.str-el)
The scaling limit of the Heisenberg XXZ spin chain at zero magnetic field is studied in the gapped antiferromagnetic phase. For a spin-chain ring having $N_x$ sites, the universal Casimir scaling function, which characterises the leading finite-size correction term in the large-$N_x$ expansion of the ground state energy, is calculated by numerical solution of the nonlinear integral equation of the convolution type. It is shown, that the same scaling function describes the temperature dependence of the free energy of the infinite XXZ chain at low enough temperatures in the gapped scaling regime.
- arXiv:1905.13666 (replaced) [pdf, other]
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Title: Topological defects at the boundary of neutron $^{3}P_{2}$ superfluids in neutron starsComments: 30 pages, 11 figuresJournal-ref: Phys. Rev. C 101, 025204 (2020)Subjects: Nuclear Theory (nucl-th); High Energy Astrophysical Phenomena (astro-ph.HE); Superconductivity (cond-mat.supr-con); High Energy Physics - Theory (hep-th)
We study surface effects of neutron $^{3}P_{2}$ superfluids in neutron stars. $^{3}P_{2}$ superfluids are in uniaxial nematic (UN), D$_{2}$ biaxial nematic (BN), or D$_{4}$ BN phase, depending on the strength of magnetic fields from small to large. We suppose a neutron $^{3}P_{2}$ superfluid in a ball with a spherical boundary. Adopting a suitable boundary condition for $^{3}P_{2}$ condensates, we solve the Ginzburg-Landau equation to find several surface properties for the neutron $^{3}P_{2}$ superfluid. First, the phase on the surface can be different from that of the bulk, and symmetry restoration or breaking occurs in general on the surface. Second, the distribution of the surface energy density has an anisotropy depending on the polar angle in the sphere, which may lead to the deformation of the geometrical shape of the surface. Third, the order parameter manifold induced on the surface, which is described by two-dimensional vector fields induced on the surface from the condensates, allows topological defects (vortices) on the surface, and there must exist such defects even in the ground state thanks to the Poincar\'{e}-Hopf theorem: although the numbers of the vortices and antivortices depend on the bulk phases, the difference between them is topologically invariant (the Euler number $\chi=2$) irrespective of the bulk phases. These vortices, which are not extended to the bulk, are called boojums in the context of liquid crystals and helium-3 superfluids. The surface properties of the neutron $^{3}P_{2}$ superfluid found in this paper may provide us useful information to study neutron stars.
- arXiv:1906.04446 (replaced) [pdf, other]
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Title: Floquet oscillations in periodically driven Dirac systemsComments: 11 pages, 7 figuresJournal-ref: Phys. Rev. B 101, 134302 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Quantum Physics (quant-ph)
Electrons in a lattice exhibit time-periodic motion, known as Bloch oscillation, when subject to an additional static electric field. Here we show that a corresponding dynamics can occur upon replacing the spatially periodic potential by a time-periodic driving: Floquet oscillations of charge carriers in a spatially homogeneous system. The time lattice of the driving gives rise to Floquet bands that take on the role of the usual Bloch bands. For two different drivings (harmonic driving and periodic kicking through pulses) of systems with linear dispersion we demonstrate the existence of such oscillations, both by directly propagating wave packets and based on a complementary Floquet analysis. The Floquet oscillations feature richer oscillation patterns than their Bloch counterpart and enable the imaging of Floquet bands. Moreover, their period can be directly tuned through the driving frequency. Such oscillations should be experimentally observable in effective Dirac systems, such as graphene, when illuminated with circularly polarized light.
- arXiv:1906.05306 (replaced) [pdf, other]
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Title: Order parameter dynamics of the non-linear sigma model in the large $N$ limitComments: typos corrected; published versionJournal-ref: Eur. Phys. J. B (2020) 93: 40Subjects: Statistical Mechanics (cond-mat.stat-mech); Strongly Correlated Electrons (cond-mat.str-el); High Energy Physics - Theory (hep-th)
We study non-equilibrium order parameter dynamics of the non-linear sigma model in the large $N$ limit, using Keldysh formalism. We provide a scheme for obtaining stable numerical solutions of the Keldysh saddle point equations, and use them to study the order parameter dynamics of the model either following a ramp, or in the presence of a periodic drive. We find that the transient dynamics of the order parameter in the presence of a periodic drive is controlled by the drive frequency displaying the phenomenon of synchronization. We also study the approach of the order parameter to its steady state value following a ramp and find out the effective temperature of the steady state. We chart out the steady state temperature of the ordered phase as a function of ramp time and amplitude, and discuss the relation of our results to experimentally realizable spin models.
- arXiv:1906.05564 (replaced) [pdf, ps, other]
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Title: Stability of the Laughlin phase against long-range interactionsSubjects: Mathematical Physics (math-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Strongly Correlated Electrons (cond-mat.str-el); Analysis of PDEs (math.AP)
A natural, "perturbative", problem in the modelization of the fractional quantum Hall effect is to minimize a classical energy functional within a variational set based on Laughlin's wave-function. We prove that, for small enough pair interactions, and asymptotically for large particle numbers, a minimizer can always be looked for in the particular form of uncorrelated quasi-holes superimposed to Laughlin's wave-function.
- arXiv:1907.01295 (replaced) [pdf, other]
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Title: Dynamical conductivity of the Fermi arc and the Volkov-Pankratov states on the surface of Weyl semimetalsComments: 9 pages, 9 figuresJournal-ref: Phys. Rev. B 100, 195412 (2019)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Weyl semimetals are known to host massless surface states called Fermi arcs. These Fermi arcs are the manifestation of the bulk-edge correspondence in topological matter and thus are analogous to the topological chiral surface states of topological insulators. It has been shown that the latter, depending on the smoothness of the surface, host massive Volkov-Pankratov(VP) states that coexist with the chiral ones. Here, we investigate these VP states in the framework of Weyl semimetals, namely their density of states and magneto-optical response. We find the selection rules corresponding to optical transitions which lead to anisotropic responses to external fields. In the presence of a magnetic field parallel to the interface, the selection rules and hence the poles of the response functions are mixed.
- arXiv:1907.02068 (replaced) [pdf, other]
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Title: Fractional Quantum Hall Effect in Weyl SemimetalsComments: 5+3 pages, 3 figures; published versionJournal-ref: Phys. Rev. Lett. 124, 096603 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el)
Weyl semimetal may be thought of as a gapless topological phase protected by the chiral anomaly, where the symmetries involved in the anomaly are the $U(1)$ charge conservation and the crystal translational symmetry. The absence of a band gap in a weakly-interacting Weyl semimetal is mandated by the electronic structure topology and is guaranteed as long as the symmetries and the anomaly are intact. The nontrivial topology also manifests in the Fermi arc surface states and topological response, in particular taking the form of an anomalous Hall effect in magnetic Weyl semimetals, whose magnitude is only determined by the location of the Weyl nodes in the Brillouin zone. Here we consider the situation when the interactions are not weak and ask whether it is possible to open a gap in a magnetic Weyl semimetal while preserving its nontrivial electronic structure topology along with the translational and the charge conservation symmetries. Surprisingly, the answer turns out to be yes. The resulting topologically ordered state provides a nontrivial realization of the fractional quantum Hall effect in three spatial dimensions in the absence of an external magnetic field, which cannot be viewed as a stack of two dimensional states. Our state contains loop excitations with nontrivial braiding statistics when linked with lattice dislocations.
- arXiv:1907.02939 (replaced) [pdf, other]
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Title: Optimal cycles for low-dissipation heat enginesComments: Accepted in PRL. 5 pages +16 Supp.MatJournal-ref: Phys. Rev. Lett. 124, 110606 (2020)Subjects: Quantum Physics (quant-ph); Statistical Mechanics (cond-mat.stat-mech)
We consider the optimization of a finite-time Carnot engine characterized by small dissipations. We bound the power with a simple inequality and show that the optimal strategy is to perform small cycles around a given working point, which can be thus chosen optimally. Remarkably, this optimal point is independent of the figure of merit combining power and efficiency that is being maximized. Furthermore, for a general class of dynamics the power output becomes proportional to the heat capacity of the working substance. Since the heat capacity can scale supra-extensively with the number of constituents of the engine, this enables us to design optimal many-body Carnot engines reaching maximum efficiency at finite power per constituent in the thermodynamic limit.
- arXiv:1908.04307 (replaced) [pdf, other]
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Title: The Hubbard model on the honeycomb lattice: from static and dynamical mean-field theories to lattice quantum Monte Carlo simulationsAuthors: Marcin Raczkowski, Robert Peters, Th\d{i} Thu Phùng, Nayuta Takemori, Fakher F. Assaad, Andreas Honecker, Javad VahediComments: 10 pages + appendix on the structure of the self energy; 5 figuresJournal-ref: Phys. Rev. B 101, 125103 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We study the one-band Hubbard model on the honeycomb lattice using a combination of quantum Monte Carlo (QMC) simulations and static as well as dynamical mean-field theory (DMFT). This model is known to show a quantum phase transition between a Dirac semi-metal and the antiferromagnetic insulator. The aim of this article is to provide a detailed comparison between these approaches by computing static properties, notably ground-state energy, single-particle gap, double occupancy, and staggered magnetization, as well as dynamical quantities such as the single-particle spectral function. At the static mean-field level local moments cannot be generated without breaking the SU(2) spin symmetry. The DMFT approximation accounts for temporal fluctuations, thus captures both the evolution of the double occupancy and the resulting local moment formation in the paramagnetic phase. As a consequence, the DMFT approximation is found to be very accurate in the Dirac semi-metallic phase where local moment formation is present and the spin correlation length small. However, in the vicinity of the fermion quantum critical point the spin correlation length diverges and the spontaneous SU(2) symmetry breaking leads to low-lying Goldstone modes in the magnetically ordered phase. The impact of these spin fluctuations on the single-particle spectral function -- \textit{waterfall} features and narrow spin-polaron bands -- is only visible in the lattice QMC approach.
- arXiv:1909.05519 (replaced) [pdf, other]
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Title: Construction and classification of point group symmetry protected topological phases in 2D interacting fermionic systemsComments: 4+epsilon pages, 4 figures, 2 tables; with supplementary material; Published versionJournal-ref: Phys. Rev. B 101, 100501 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); High Energy Physics - Theory (hep-th)
The construction and classification of symmetry-protected topological (SPT) phases in interacting bosonic and fermionic systems have been intensively studied in the past few years. Very recently, a complete classification and construction of space group SPT phases were also proposed for interacting bosonic systems. In this paper, we attempt to generalize this classification and construction scheme systematically into interacting fermion systems. In particular, we construct and classify point group SPT phases for 2D interacting fermion systems via lower-dimensional block-state decorations. We discover several intriguing fermionic SPT states that can only be realized in interacting fermion systems (i.e., not in free-fermion or bosonic SPT systems). Moreover, we also verify the recently conjectured crystalline equivalence principle for 2D interacting fermion systems. Finally, the potential experimental realization of these new classes of point group SPT phases in 2D correlated superconductors is addressed.
- arXiv:1909.09507 (replaced) [pdf, other]
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Title: Phenomenology of anomalous transport in disordered one-dimensional systemsComments: Close to published version. 9 pages, 9 figuresJournal-ref: J. Stat. Mech. (2020) 023107Subjects: Disordered Systems and Neural Networks (cond-mat.dis-nn); Strongly Correlated Electrons (cond-mat.str-el)
We study anomalous transport arising in disordered one-dimensional spin chains, specifically focusing on the subdiffusive transport typically found in a phase preceding the many-body localization transition. Different types of transport can be distinguished by the scaling of the average resistance with the system's length. We address the following question: what is the distribution of resistance over different disorder realizations, and how does it differ between transport types? In particular, an often evoked so-called Griffiths picture, that aims to explain slow transport as being due to rare regions of high disorder, would predict that the diverging resistivity is due to fat power-law tails in the resistance distribution. Studying many-particle systems with and without interactions we do not find any clear signs of fat tails. The data is compatible with distributions that decay faster than any power law required by the fat tails scenario. Among the distributions compatible with the data, a simple additivity argument suggests a Gaussian distribution for a fractional power of the resistance.
- arXiv:1909.09550 (replaced) [pdf, other]
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Title: Distinguishing phases using the dynamical response of driven-dissipative light-matter systemsComments: 10 pages, 4 figures, main body plus six appendicesJournal-ref: Phys. Rev. A 101, 023823 (2020)Subjects: Quantum Gases (cond-mat.quant-gas); Quantum Physics (quant-ph)
We present a peculiar transition triggered by infinitesimal dissipation in the interpolating Dicke-Tavis-Cummings model. The model describes a ubiquitous light-matter setting using a collection of two-level systems interacting with quantum light trapped in an optical cavity. In a previous work [Phys. Rev. Lett. 120, 183603 (2018)], dissipation was shown to extend a normal phase (dark state) into new regions of the model's parameter space. Harnessing Keldysh's action formalism to compute the response function of the light, we show that the normal phase does not merely spread but encompasses a transition between the old and the dissipation-stabilized regimes of the normal phase. This transition, however, solely manifests in the dynamical fluctuations atop the empty cavity, through stabilization of an excited state of the closed system. Consequently, we reveal that the fluctuations flip from being particlelike to holelike across this transition. This inversion is also accompanied by the behavior of the Liouvillian eigenvalues akin to exceptional points. Our work forges the way to discovering transitions in a wide variety of driven-dissipative systems and is highly pertinent for current experiments.
- arXiv:1910.01131 (replaced) [pdf, other]
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Title: Correspondence between winding numbers and skin modes in non-hermitian systemsComments: 19 pages, 9 figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We establish exact relations between the winding of "energy" (eigenvalue of Hamiltonian) on the complex plane as momentum traverses the Brillouin zone with periodic boundary condition, and the presence of "skin modes" with open boundary condition in non-hermitian systems. We show that the nonzero winding with respect to any complex reference energy leads to the presence of skin modes, and vice versa. We also show that both the nonzero winding and the presence of skin modes share the common physical origin that is the non-vanishing current through the system.
- arXiv:1910.06496 (replaced) [pdf, other]
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Title: Hall Viscosity of Composite FermionsComments: 19 pages, 9 figuresJournal-ref: Phys. Rev. Research 2, 013139 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Mathematical Physics (math-ph)
Hall viscosity, also known as the Lorentz shear modulus, has been proposed as a topological property of a quantum Hall fluid. Using a recent formulation of the composite fermion theory on the torus, we evaluate the Hall viscosities for a large number of fractional quantum Hall states at filling factors of the form $\nu=n/(2pn\pm 1)$, where $n$ and $p$ are integers, from the explicit wave functions for these states. The calculated Hall viscosities $\eta^A$ agree with the expression $\eta^A=(\hbar/4) {\cal S}\rho$, where $\rho$ is the density and ${\cal S}=2p\pm n$ is the "shift" in the spherical geometry. We discuss the role of modular invariance of the wave functions, of the center-of-mass momentum, and also of the lowest-Landau-level projection. Finally, we show that the Hall viscosity for $\nu={n\over 2pn+1}$ may be derived analytically from the microscopic wave functions, provided that the overall normalization factor satisfies a certain behavior in the thermodynamic limit. This derivation should be applicable to a class of states in the parton construction, which are products of integer quantum Hall states with magnetic fields pointing in the same direction.
- arXiv:1910.09556 (replaced) [pdf, other]
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Title: Analytical theory of pyrochlore cooperative paramagnetsComments: 7 pages, 4 figuresJournal-ref: Phys. Rev. B 101, 115107 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el)
The pyrochlore lattice is associated with several potential and actual spin liquid phases as a result of its strong geometric frustration. At finite temperature, these can exhibit an unusually broad cross-over regime to a conventional paramagnet. Here, we study this regime analytically by showing how a single-tetrahedron Hamiltonian can extrapolate beyond the first term of a high-temperature expansion and yield insights into the build-up of correlations. We discuss how this unusual behaviour is brought about by the structure of the eigenspaces of the coupling matrix. Further interesting behaviour can appear for parameter values located near phase transitions: we find coexistence of $(111)$ rods and $(220)$ peaks in the structure factor, as observed in neutron scattering experiments on Yb$_2$Ti$_2$O$_7$.
- arXiv:1910.10813 (replaced) [pdf, other]
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Title: Fast relaxation on qutrit transitions of nitrogen-vacancy centers in nanodiamondsComments: Main text: 8 pages, 4 figures, 1 table, 37 references. Supplemental materials: 5 pages, 8 figures, 1 table. Changes in v4: Accepted manuscriptJournal-ref: Phys. Rev. Applied 13, 034010 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Quantum Physics (quant-ph)
Thanks to their versatility, nitrogen-vacancy (NV) centers in nanodiamonds have been widely adopted as nanoscale sensors. However, their sensitivities are limited by their short coherence times relative to NVs in bulk diamond. A more complete understanding of the origins of decoherence in nanodiamonds is critical to improving their performance. Here we present measurements of fast spin relaxation on qutrit transitions between the energy eigenstates composed of the $m_s = \pm1$ states of the NV$^-$ electronic ground state in $\sim40$-nm nanodiamonds under ambient conditions. For frequency splittings between these states of $\sim20~$MHz or less the maximum theoretically achievable coherence time of the NV spin is $\sim2~$orders of magnitude shorter than would be expected if the NV spin is treated as a qubit. We attribute this fast relaxation to electric field noise. We observe a strong falloff of the qutrit relaxation rate with the splitting between the states, suggesting that, whenever possible, measurements with NVs in nanodiamonds should be performed at moderate axial magnetic fields ($>60$ G). We also observe that the qutrit relaxation rate changes with time. These findings indicate that surface electric field noise is a major source of decoherence for NVs in nanodiamonds.
- arXiv:1911.06767 (replaced) [pdf, other]
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Title: Exact non-adiabatic part of the Kohn-Sham potential and its fluidic approximationComments: 5 pages, 4 figures + 2 page supplemental material with 5 .mp4 filesJournal-ref: Phys. Rev. Materials 4, 035002 (2020)Subjects: Chemical Physics (physics.chem-ph); Other Condensed Matter (cond-mat.other)
We present a simple geometrical "fluidic" approximation to the non-adiabatic part of the Kohn-Sham potential, $v_{\mathrm{KS}}$, of time-dependent density functional theory. This part of $v_{\mathrm{KS}}$ is often crucial, but most practical functional approximations utilize an adiabatic approach based on ground-state DFT. For a variety of prototype systems, we calculate the exact time-dependent electron density, and find that the fluidic approximation corrects a large part of the error arising from the "exact adiabatic" approach, even when the system is evolving far from adiabatically.
- arXiv:1911.07459 (replaced) [pdf, other]
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Title: Interaction-impeded relaxation in the presence of finite temperature bathsComments: 5 pages, 4 figuresJournal-ref: Phys. Rev. A 101, 023603 (2020)Subjects: Quantum Physics (quant-ph); Quantum Gases (cond-mat.quant-gas); Statistical Mechanics (cond-mat.stat-mech)
We study the interplay between interactions and finite-temperature dephasing baths. We consider a double well with strongly interacting bosons coupled, via the density, to a bosonic bath. Such a system, when the bath has infinite temperature and instantaneous decay of correlations, relaxes with an emerging algebraic behavior with exponent 1/2. Here we show that, because of the finite-temperature baths and of the choice of spectral densities, such an algebraic relaxation may occur for a shorter duration and the characteristic exponent can be lower than 1/2. These results show that the interaction-induced impeding of relaxation is stronger and more complex when the bath has finite temperature and/or nonzero timescale for the decay of correlations.
- arXiv:1911.09521 (replaced) [pdf, other]
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Title: Schottky barrier lowering due to interface states in 2D heterophase devicesComments: 5 figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci)
The Schottky barrier of a metal-semiconductor junction is one of the key quantities affecting the charge transport in a transistor. The Schottky barrier height depends on several factors, such as work function difference, local atomic configuration in the interface, and impurity doping. We show that also the presence of interface states at 2D metal-semiconductor junctions can give rise to a large renormalization of the effective Schottky barrier determined from the temperature dependence of the current (IT-characteristic). We investigate the charge transport in n- and p-doped monolayer MoTe$_2$ 1T'-1H junctions using ab-initio quantum transport calculations. The Schottky barriers are extracted both from the projected density of states and the transmission spectrum, and by simulating the IT-characteristic and applying the thermionic emission model. We find that barrier tunneling mediated by localized interface states can lower the effective barrier to a value of only 55 meV. Our results can help to understand the long-standing disagreements between the calculated and measured Schottky barriers of these systems. We propose that the small values of the measured barriers are not due to a perfect line-up of the bands in the two phases but due to large tunneling currents.
- arXiv:1911.11204 (replaced) [pdf, other]
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Title: Energy-efficient stochastic computing with superparamagnetic tunnel junctionsComments: 20 pages (12 pages main text), 12 figuresJournal-ref: Phys. Rev. Applied 13, 034016 (2020)Subjects: Emerging Technologies (cs.ET); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Applied Physics (physics.app-ph)
Superparamagnetic tunnel junctions (SMTJs) have emerged as a competitive, realistic nanotechnology to support novel forms of stochastic computation in CMOS-compatible platforms. One of their applications is to generate random bitstreams suitable for use in stochastic computing implementations. We describe a method for digitally programmable bitstream generation based on pre-charge sense amplifiers. This generator is significantly more energy efficient than SMTJ-based bitstream generators that tune probabilities with spin currents and a factor of two more efficient than related CMOS-based implementations. The true randomness of this bitstream generator allows us to use them as the fundamental units of a novel neural network architecture. To take advantage of the potential savings, we codesign the algorithm with the circuit, rather than directly transcribing a classical neural network into hardware. The flexibility of the neural network mathematics allows us to adapt the network to the explicitly energy efficient choices we make at the device level. The result is a convolutional neural network design operating at $\approx$ 150 nJ per inference with 97 % performance on MNIST -- a factor of 1.4 to 7.7 improvement in energy efficiency over comparable proposals in the recent literature.
- arXiv:1912.01474 (replaced) [pdf, ps, other]
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Title: Exciton dynamics in different aromatic hydrocarbon systemsAuthors: Milica Rutonjski, Petar Mali, Slobodan Radosevic, Sonja Gombar, Milan Pantic, Milica Pavkov-HrvojevicComments: 6 pages, 8 figures, 2 tablesSubjects: Materials Science (cond-mat.mtrl-sci); Strongly Correlated Electrons (cond-mat.str-el)
The exciton dispersion is examined in the case of four selected prototypical molecular solids: pentacene,tetracene,picene,chrysene. The model parameters are determined by fitting to experimental data obtained by inelastic electron scattering. Within the picture that relies on Frenkel-type excitons we obtain that theoretical dispersion curves along different directions in the Brillouin zone are in good agreement with the experimental data, suggesting that the influence of charge-transfer excitons on exciton dispersion of the analyzed organic solids is not as large as proposed. In reciprocal space directions where Davydov splitting is observed we employ the upgraded version of Hamiltonian used in Materials 11, 2219 (2018).
- arXiv:1912.11222 (replaced) [pdf]
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Title: A picture of pseudogap phase related to charge fluxesSubjects: Superconductivity (cond-mat.supr-con)
Recently, charge density fluctuations or charge fluxes attract strong interests in understanding the unconventional superconductivity. In this paper, a new emergent configuration in cuprates is identified by density functional theory simulations, called the charge pseudoplane, which exhibits the property of confining the dynamic charge flux flows. It further redefines the fundamental collective excitation in cuprates with the momentum-dependent and ultrafast localization-delocalization duality. It is shown that both pseudogap and superconducting phases can be born from and intertwined through the charge flux confinement property of the charge pseudoplane. Our experimental simulations based on the new picture provide good agreements with previous experimental results. Our work thus opens a new perspective to understand the origin of pseudogap phase and other related phases in cuprates, and further provides a critical descriptor to search and design higher temperature superconductors.
- arXiv:2001.00026 (replaced) [pdf, other]
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Title: The 2020 Skyrmionics RoadmapAuthors: C. Back, V. Cros, H. Ebert, K. Everschor-Sitte, A. Fert, M. Garst, Tianping Ma, S. Mankovsky, T. L. Monchesky, M. Mostovoy, N. Nagaosa, S.S.P. Parkin, C. Pfleiderer, N. Reyren, A. Rosch, Y. Taguchi, Y. Tokura, K. von Bergmann, Jiadong ZangComments: J. Phys. D, accepted for publicationSubjects: Strongly Correlated Electrons (cond-mat.str-el); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); High Energy Physics - Phenomenology (hep-ph); Nuclear Theory (nucl-th)
The notion of non-trivial topological winding in condensed matter systems represents a major area of present-day theoretical and experimental research. Magnetic materials offer a versatile platform that is particularly amenable for the exploration of topological spin solitons in real space such as skyrmions. First identified in non-centrosymmetric bulk materials, the rapidly growing zoology of materials systems hosting skyrmions and related topological spin solitons includes bulk compounds, surfaces, thin films, heterostructures, nano-wires and nano-dots. This underscores an exceptional potential for major breakthroughs ranging from fundamental questions to applications as driven by an interdisciplinary exchange of ideas between areas in magnetism which traditionally have been pursued rather independently. The skyrmionics roadmap provides a review of the present state of the art and the wide range of research directions and strategies currently under way. These are, for instance, motivated by the identification of the fundamental structural properties of skyrmions and related textures, processes of nucleation and annihilation in the presence of non-trivial topological winding, an exceptionally efficient coupling to spin currents generating spin transfer torques at tiny current densities, as well as the capability to purpose-design broad-band spin dynamic and logic devices.
- arXiv:2001.01009 (replaced) [pdf, other]
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Title: Observation of the Interlayer Exciton Gases in WSe$_2$ -pWSe$_2$ HeterostructuresAuthors: Zheng Sun, Jonathan Beaumariage, Qingrui Cao, Kenji Watanabe, Takashi Taniguchi, Benjamin Hunt, David W SnokeSubjects: Materials Science (cond-mat.mtrl-sci); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Interlayer excitons (IXs) possess a much longer lifetime than intralayer excitons due to the spatial separation of the electrons and holes; hence, they have been pursued to create exciton condensates for decades. The recent emergence of two-dimensional (2D) materials, such as transition metal dichalcogenides (TMDs), and of their van der Waals heterostructures (HSs), in which two different 2D materials are layered together, has created new opportunities to study IXs. Here we present the observation of IX gases within two stacked structures consisting of hBN/WSe$_2$/hBN/p: WSe$_2$/hBN. The IX energy of the two different structures differed by 82 meV due to the different thickness of the hBN spacer layer between the TMD layers. We demonstrate that the lifetime of the IXs is shortened when the temperature decreases or when the pump power increases. We attribute this nonlinear behavior to an Auger process.
- arXiv:2001.01790 (replaced) [pdf, other]
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Title: Controllable skyrmion chirality in ferroelectricsAuthors: Yu. Tikhonov, S. Kondovych, J. Mangeri, M. Pavlenko, L. Baudry, A. Sené, A. Galda, S. Nakhmanson, O. Heinonen, A. Razumnaya, I. Luk'yanchuk, V.M. VinokurSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Chirality, an intrinsic handedness, is one of the most intriguing fundamental phenomena in nature. Materials composed of chiral molecules find broad applications in areas ranging from nonlinear optics and spintronics to biology and pharmaceuticals. However, chirality is usually an invariable inherent property of a given material that cannot be easily changed at will. Here, we demonstrate that ferroelectric nanodots support skyrmions the chirality of which can be controlled and switched. We devise protocols for realizing control and efficient manipulations of the different types of skyrmions. Our findings open the route for controlled chirality with potential applications in ferroelectric-based information technologies.
- arXiv:2001.02926 (replaced) [pdf, other]
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Title: Block-Lanczos density-matrix renormalization-group approach to spin transport in Heisenberg chains coupled to leadsComments: 6 pages, 6 figures, final versionJournal-ref: J. Phys. Soc. Jpn. 89, 044601 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el)
We adapt the block-Lanczos density-matrix renormalization-group technique to study the spin transport in a spin chain coupled to two non-interacting fermionic leads. As an example, we consider leads described by two-dimensional tight-binding models on a square lattice. Although the simulations are carried out using a chain representation of the leads, observables in the original two-dimensional lattice can be calculated by reversing the block-Lanczos transformation. This is demonstrated for leads with Rashba spin-orbit coupling.
- arXiv:2001.03902 (replaced) [pdf, other]
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Title: Magnetic Skyrmions in FePt Square-Based Nanoparticles Around Room-TemperatureComments: 11 pages,12 Figures, research articleSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Magnetic skyrmions formed around room-temperature in square-based parallelepiped magnetic nanoparticles with perpendicular magnetocrystalline anisotropy similar to that of partially chemically ordered FePt were studied during the magnetization reversal using micromagnetic simulations. Finite Differences (FD) discretizations were used for the solution of the Landau-Lifshitz-Gilbert equation. Magnetic configurations exhibiting N\'eel chiral stripe and N\'eel skyrmionic formations were detected. The magnetic skyrmions can be created in different systems generated by the variation of external field, side length and width of the squared-based parallelepiped magnetic nanoparticles. Micromagnetic configurations revealed a variety of states which include skyrmionic textures with one distinct skyrmion formed and being stable for a range of external fields around room-temperature. The size of the formed N\'eel skyrmion is calculated as a function of the external field, temperature, magnetocrystalline anisotropy and nanoparticle's geometrical characteristic lengths which can be adjusted to produce N\'eel type skyrmions on demand having diameters down to 12 nm. The micromagnetic simulations revealed that stable skyrmions at the temperature range 270K-330K can be created for FePt magnetic nanoparticle systems lacking of chiral interactions such as Dzyaloshinsky-Moriya, providing new perspectives in the new magnetic writing era.
- arXiv:2001.08908 (replaced) [pdf, other]
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Title: From latent ferroelectricity to hyperferroelectricity in alkali lead halide perovskitesSubjects: Materials Science (cond-mat.mtrl-sci)
Using first principles calculations we show that several alkali lead halides potentially present collective ferroelectric polarization. This should occur at least at the nanoscale; it could be detected macroscopically provided it is not concealed by lattice vibrations in the temperature range of stability of the cubic perovskite phase. For potassium lead halides and for alkali lead fluorides, remarkably, the ferroelectric behavior turns hyper-ferroelectric, suggesting a more robust ferroelectric polarization in spite of depolarization potentials induced by charge accumulation on surfaces or interfaces.
- arXiv:2002.03200 (replaced) [pdf, other]
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Title: Free-space sub-terahertz field-polarization controlled by waveguide-mode-selectionComments: 14 pages including references. Comments welcome!Subjects: Quantum Physics (quant-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We study experimentally the free-space electro-magnetic field emitted from a multi-mode rectangular waveguide equipped with a diagonal-horn antenna. Using the frequency range of 215-580 GHz, a photo mixer is used to launch a free-space circularly-polarized electro-magnetic field, exciting multiple modes at the input of the rectangular waveguide via an input diagonal-horn antenna. A second photo mixer is used, together with a silicon mirror acting as Fresnel scatterer, to act as a polarization-sensitive coherent detector to characterize the emitted field. We find that the radiated field, excited by the fundamental waveguide mode, is characterized by a linear polarization. In addition, we find, unexpectedly, that the polarization rotates by 45 degrees if selectively exciting higher-order modes in the waveguide. We discuss a possible application of this new finding.
- arXiv:2002.12285 (replaced) [pdf, other]
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Title: Photon-mediated Peierls Transition of a 1D Gas in a Multimode Optical CavityComments: 6 pages, 2 figures; supplement of 4 pages; V2 includes additional referencesSubjects: Quantum Gases (cond-mat.quant-gas); Strongly Correlated Electrons (cond-mat.str-el); Quantum Physics (quant-ph)
The Peierls instability toward a charge density wave is a canonical example of phonon-driven strongly correlated physics and is intimately related to topological quantum matter and exotic superconductivity. We propose a method to realize an analogous photon-mediated Peierls transition. We consider a system of one-dimensional tubes of interacting Bose or Fermi atoms trapped inside a multimode optical cavity. Pumping the cavity transversely engineers a cavity-mediated metal--to--insulator transition in the atomic system. For the case of strongly interacting bosons in the Tonks-Girardeau limit, this transition can be understood (through fermionization) as being the Peierls instability. We extend our results away from this limit to finite values of the interaction strength as well as to interacting fermions. Both the cavity field and the mass gap display nontrivial power law dependence on the dimensionless matter-light coupling constant.
- arXiv:1703.03910 (replaced) [pdf, ps, other]
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Title: Non-linear stationary solutions in realistic models for analog black-hole lasersAuthors: Juan Ramón Muñoz de NovaComments: 28 pages, 8 figuresJournal-ref: Universe 3, 54 (2017)Subjects: Quantum Gases (cond-mat.quant-gas); General Relativity and Quantum Cosmology (gr-qc); Optics (physics.optics)
From both a theoretical and an experimental point of view, Bose-Einstein condensates are good candidates for studying gravitational analogues of black holes and black-hole lasers. In particular, a recent experiment has shown that a black-hole laser configuration can be created in the laboratory. However, the most considered theoretical models for analog black-hole lasers are quite difficult to implement experimentally. In order to fill this gap, we devote this work to present more realistic models for black-hole lasers. For that purpose, we first prove that, by symmetrically extending every black-hole configuration, one can obtain a black-hole laser configuration with an arbitrarily large supersonic region. Based on this result, we propose the use of an attractive square well and a double delta-barrier, which can be implemented using standard experimental tools, for studying black-hole lasers. We also compute the different stationary states of these setups, identifying the true ground state of the system and discussing the relation between the obtained solutions and the appearance of dynamical instabilities.
- arXiv:1808.09480 (replaced) [pdf, other]
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Title: Phases and phase transitions of Bose condensed lightJournal-ref: NJP 21, 083009 August 2019 (more detailed version)Subjects: Quantum Gases (cond-mat.quant-gas)
Bose-Einstein condensation of light in 2D is characterized by two classical fields corresponding to two polarizations of light as well as by the distribution of dye molecules inducing light thermalization through dipolar transition. In the case when this transition is triple-degenerate the resulting field theory for the condensate of light is O(4) symmetric, which precludes algebraic long range order in 2D at any finite temperature $T$. If the dipolar degeneracy is removed, then, equilibrium phases with lower symmetries -- O(2)$\times$Z$_2$ and O(2) can emerge. Accordingly, algebraic off diagonal order of light condensate becomes possible. An orientationsl disorder introduced by local dipolar anisotropy can destroy algebraic order in one-photon density matrix while preserving it in the two-photon one. This represents formation of the condensate of photon pairs.
- arXiv:1812.09066 (replaced) [pdf, other]
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Title: Marvels and Pitfalls of the Langevin Algorithm in Noisy High-dimensional InferenceAuthors: Stefano Sarao Mannelli, Giulio Biroli, Chiara Cammarota, Florent Krzakala, Pierfrancesco Urbani, Lenka ZdeborováComments: 11 pages and 5 figures + appendixJournal-ref: Phys. Rev. X 10, 011057 (2020)Subjects: Machine Learning (cs.LG); Disordered Systems and Neural Networks (cond-mat.dis-nn); Statistics Theory (math.ST); Machine Learning (stat.ML)
Gradient-descent-based algorithms and their stochastic versions have widespread applications in machine learning and statistical inference. In this work we perform an analytic study of the performances of one of them, the Langevin algorithm, in the context of noisy high-dimensional inference. We employ the Langevin algorithm to sample the posterior probability measure for the spiked matrix-tensor model. The typical behaviour of this algorithm is described by a system of integro-differential equations that we call the Langevin state evolution, whose solution is compared with the one of the state evolution of approximate message passing (AMP). Our results show that, remarkably, the algorithmic threshold of the Langevin algorithm is sub-optimal with respect to the one given by AMP. We conjecture this phenomenon to be due to the residual glassiness present in that region of parameters. Finally we show how a landscape-annealing protocol, that uses the Langevin algorithm but violate the Bayes-optimality condition, can approach the performance of AMP.
- arXiv:1903.05995 (replaced) [pdf]
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Title: Interplay of Spin, Lattice, and Charge Degrees of Freedom in Ca3Mn2O7Comments: 16 pages, 7 figures, 32 referencesJournal-ref: Journal of the American Ceramic Society 103(3), 3238-3248 (2020)Subjects: Materials Science (cond-mat.mtrl-sci)
From low-temperature Synchrotron X-ray diffraction, a precise thermal characterization of octahedral distortions in single phase Ruddlesden-Popper Ca3Mn2O7 is performed. Highly sensitive close-steps temperature dependences of Mn-O-Mn bond angles connecting MnO6 octahedra clearly reveal signature of the spin-ordering in the system. Spin-lattice coupling is thus established via the structural distortions responsible for evolution of the magnetic state. Further, temperature anomalies observed here in volume and polarization-measure of the unit cell highlight the interplay between spin, lattice and charge degrees of freedom. Dipole-relaxation characteristics examined under applied magnetic field consistently corroborate the concurrent magnetic and structural changes, in terms of genuine and intrinsic magneto-dielectricity.
- arXiv:1903.11368 (replaced) [pdf, other]
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Title: Out-of-equilibrium operation of a quantum heat engine: The cost of thermal coupling controlSubjects: Quantum Physics (quant-ph); Statistical Mechanics (cond-mat.stat-mech)
Real quantum heat engines lack the separation of time and length scales that is characteristic for classical engines. They must be understood as open quantum systems in non-equilibrium with time-controlled coupling to thermal reservoirs as integral part. Here, we present a systematic approach to describe a broad class of engines and protocols beyond conventional weak coupling treatments starting from a microscopic modeling. For the four stroke Otto engine the full dynamical range down to low temperatures is explored and the crucial role of the work associated with the coupling/decoupling to/from reservoirs in the energy balance is revealed. Quantum correlations turn out to be instrumental to enhance the efficiency which opens new ways for optimal control techniques.
- arXiv:1905.01850 (replaced) [pdf]
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Title: Observation of discrete conventional Caroli-de Gennes-Matricon states in the vortex core of single-layer FeSe/SrTiO3Comments: 10 pages, 5 figures, supplementary materials includedJournal-ref: Phys. Rev. Lett. 124, 097001 (2020)Subjects: Superconductivity (cond-mat.supr-con); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Strongly Correlated Electrons (cond-mat.str-el)
Using low-temperature scanning tunneling microscopy (STM), we studied the vortex states of single-layer FeSe film on SrTiO3 (100) substrate, and the local behaviors of superconductivity at sample boundaries. We clearly observed multiple discrete Caroli-de Gennes-Matricon (CdGM) states in the vortex core, and quantitative analysis shows their energies well follow the formula: E = {\mu}{\Delta}^2/E_F, where {\mu} is a half integer and {\Delta} is the mean superconducting gap over the Fermi surface. Meanwhile, a fully gapped spectrum without states near zero bias is observed at [110](Fe) oriented boundary of 1 ML and 2 ML FeSe films, and atomic step edge of 1 ML FeSe. Accompanied with theoretical calculations, our results indicate a s-wave pairing without sign-change in the high-TC FeSe_SrTiO3 superconductor.
- arXiv:1907.00424 (replaced) [pdf, other]
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Title: Non-linear spin torque, pumping and cooling in superconductor/ferromagnet systemsComments: 6 pages, 4 figuresJournal-ref: Phys. Rev. B 101, 115406 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We study the effects of the coupling between magnetization dynamics and the electronic degrees of freedom in a heterostructure of a metallic nanomagnet with dynamic magnetization coupled with a superconductor containing a steady spin-splitting field. We predict how this system exhibits a non-linear spin torque, which can be driven either with a temperature difference or a voltage across the interface. We generalize this notion to arbitrary magnetization precession by deriving a Keldysh action for the interface, describing the coupled charge, heat and spin transport in the presence of a precessing magnetization. We characterize the effect of superconductivity on the precession damping and the anti-damping torques. We also predict the full non-linear characteristic of the Onsager counterparts of the torque, showing up via pumped charge and heat currents. For the latter, we predict a spin-pumping cooling effect, where the magnetization dynamics can cool either the nanomagnet or the superconductor.
- arXiv:1909.00992 (replaced) [pdf, ps, other]
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Title: Quasiclassical expressions for the free energy of superconducting systemsComments: 7 pagesJournal-ref: Phys. Rev. B 101, 094507 (2020)Subjects: Superconductivity (cond-mat.supr-con)
In the seminal work by G. Eilenberger [Z. Phys. 214, 195 (1968)], the quasiclassical expression for the free energy of spin-singlet superconductor has been suggested. Starting from the Luttinger-Ward formulation we derive the Eilenberger free energy and find its generalization for superconductor or superfluid with spin-triplet correlations. Besides ordinary superconductors with various scattering mechanisms, the obtained free energy functional can be used for systems with spin-triplet pairing such as superfluid $^3$He and superconducting systems with spatially-inhomogeneous exchange field or spin-orbit coupling. Using this general result we derive the simplified expression for the free energy in the diffusive limit in terms of the momentum-averaged propagators.
- arXiv:1909.02841 (replaced) [pdf, ps, other]
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Title: Front dynamics in the XY chain after local excitationsComments: 28 pages, 8 figures, minor changesJournal-ref: SciPost Phys. 8, 037 (2020)Subjects: Statistical Mechanics (cond-mat.stat-mech); Quantum Physics (quant-ph)
We study the time evolution of magnetization and entanglement for initial states with local excitations, created upon the ferromagnetic ground state of the XY chain. For excitations corresponding to a single or two well separated domain walls, the magnetization profile has a simple hydrodynamic limit, which has a standard interpretation in terms of quasiparticles. In contrast, for a spin-flip we obtain an interference term, which has to do with the nonlocality of the excitation in the fermionic basis. Surprisingly, for the single domain wall the hydrodynamic limit of the entropy and magnetization profiles are found to be directly related. Furthermore, the entropy profile is additive for the double domain wall, whereas in case of the spin-flip excitation one has a nontrivial behaviour.
- arXiv:1909.07641 (replaced) [pdf, other]
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Title: Realizing a scalable building block of a U(1) gauge theory with cold atomic mixturesAuthors: Alexander Mil, Torsten V. Zache, Apoorva Hegde, Andy Xia, Rohit P. Bhatt, Markus K. Oberthaler, Philipp Hauke, Jürgen Berges, Fred JendrzejewskiSubjects: Quantum Gases (cond-mat.quant-gas); High Energy Physics - Phenomenology (hep-ph); Atomic Physics (physics.atom-ph); Quantum Physics (quant-ph)
In the fundamental laws of physics, gauge fields mediate the interaction between charged particles. An example is quantum electrodynamics -- the theory of electrons interacting with the electromagnetic field -- based on U(1) gauge symmetry. Solving such gauge theories is in general a hard problem for classical computational techniques. While quantum computers suggest a way forward, it is difficult to build large-scale digital quantum devices required for complex simulations. Here, we propose a fully scalable analog quantum simulator of a U(1) gauge theory in one spatial dimension. To engineer the local gauge symmetry, we employ inter-species spin-changing collisions in an atomic mixture. We demonstrate the experimental realization of the elementary building block as a key step towards a platform for large-scale quantum simulations of continuous gauge theories.
- arXiv:1910.02929 (replaced) [pdf]
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Title: Thermal conductivity of graphene polymorphs and compounds: from C3N to graphdiyne latticesJournal-ref: Volume 161, May 2020, Pages 816-826Subjects: Materials Science (cond-mat.mtrl-sci)
Tremendous experimental and theoretical attempts to find carbon based two-dimensional semiconductors have yielded a wide variety of graphene polymorphs, such as carbon-nitride, carbonboride, graphyne and graphdiyne 2D materials with highly attractive physical and chemical properties. In this study, by conducting extensive non-equilibrium molecular dynamics simulations, we have calculated and compared the thermal conductivity of thirteen prominent carbon-based structures at different lengths and two main chirality directions. Acquired results show that the structures of C3N, C3B and C2N exhibit the highest thermal conductivity, respectively, which suggest them as suitable candidates for thermal management systems in order to enhance the heat dissipation rates. In contrast, generally graphdiyne lattices and in particular 18-6-Gdy graphdiyne yields the lowest thermal conductivity, which can be a promising feature for thermoelectric applications. As a remarkable finding, we could establish connections between the thermal conductivity and density or Young's modulus of carbon based 2D systems, which can be employed to estimate the thermal conductivity of other polymorphs. Those results can provide a comprehensive viewpoint on the thermal transport properties of the nonporous and exceedingly porous carbon based 2D materials and may be used as useful guides for future designs in thermal management.
- arXiv:1910.03184 (replaced) [pdf]
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Title: Correlated fluctuations in spin orbit torque-coupled perpendicular nanomagnetsJournal-ref: Phys. Rev. B 101, 094405 (2020)Subjects: Applied Physics (physics.app-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Low barrier nanomagnets have attracted a lot of research interest for their use as sources of high quality true random number generation. More recently, low barrier nanomagnets with tunable output have been shown to be a natural hardware platform for unconventional computing paradigms such as probabilistic spin logic. Efficient generation and tunability of high quality random bits is critical for these novel applications. However, current spintronic random number generators are based on superparamagnetic tunnel junctions (SMTJs) with tunability obtained through spin transfer torque (STT), which unavoidably leads to challenges in designing concatenated networks using these two terminal devices. The more recent development of utilizing spin orbit torque (SOT) allows for a three terminal device design, but can only tune in-plane magnetization freely, which is not very energy efficient due to the needs of overcoming a large demagnetization field. In this work, we experimentally demonstrate for the first time, a stochastic device with perpendicular magnetic anisotropy (PMA) that is completely tunable by SOT without the aid of any external magnetic field. Our measurements lead us to hypothesize that a tilted anisotropy might be responsible for the observed tunability. We carry out stochastic Landau-Lifshitz-Gilbert (sLLG) simulations to confirm our experimental observation. Finally, we build an electrically coupled network of two such stochastic nanomagnet based devices and demonstrate that finite correlation or anti-correlation can be established between their output fluctuations by a weak interconnection, despite having a large difference in their natural fluctuation time scale. Simulations based on a newly developed dynamical model for autonomous circuits composed of low barrier nanomagnets show close agreement with the experimental results.
- arXiv:1910.11234 (replaced) [pdf, other]
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Title: Segregation and Preferential Sputtering of Cr in WCrY Smart AlloyComments: 28 pages, 7 figuresSubjects: Materials Science (cond-mat.mtrl-sci)
The temperature driven segregation of Cr to the surface of the tungsten-based WCrY alloy is analysed with low energy ion scattering of He+ ions with an energy of 1 keV in the temperature range from room temperature to 1000 K. Due to the high surface sensitivity, these measurements probe only the composition of the outermost monolayer. The surface concentration of Cr increases slightly when the temperature of the sample is increased up to 700 K and exhibits a much stronger increase when the sample temperature is further raised. The segregation enthalpy for Cr is obtained from the Langmuir-McLean relation and amounts to 0.7 eV. The surface concentration of Y shows a similar behaviour to the Cr concentration. The temperature thresholds between slow and accelerated surface density increases for Cr and Y are nearly the same. At a temperature of 1000 K the low energy ion scattering detects almost no W on the surface. The modified surface composition due to the segregated species, i.e. the mixed Cr/Y layer, stays stable during cool-down of the sample. Preferential sputtering is investigated using ion bombardment of 250 eV D atoms, resulting in an increase of the W surface density at room temperature. This effect is counteracted at elevated temperatures where segregation replenishes the lighter elements on the surface and prevents the formation of an all-W surface layer. The flux of segregating Cr atoms towards the surface is evaluated from the equilibrium between sputter erosion and segregation.
- arXiv:1910.14099 (replaced) [pdf, other]
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Title: Notes on the complex Sachdev-Ye-Kitaev modelComments: v2: 75 pages, 14 figures, new appendix A.6 and references added; v1: 73 pages, 13 figures, 1 spooky propagatorJournal-ref: JHEP 02 (2020) 157Subjects: High Energy Physics - Theory (hep-th); Strongly Correlated Electrons (cond-mat.str-el)
We describe numerous properties of the Sachdev-Ye-Kitaev model for complex fermions with $N\gg 1$ flavors and a global U(1) charge. We provide a general definition of the charge in the $(G,\Sigma)$ formalism, and compute its universal relation to the infrared asymmetry of the Green function. The same relation is obtained by a renormalization theory. The conserved charge contributes a compact scalar field to the effective action, from which we derive the many-body density of states and extract the charge compressibility. We compute the latter via three distinct numerical methods and obtain consistent results. Finally, we present a two dimensional bulk picture with free Dirac fermions for the zero temperature entropy.
- arXiv:1912.01470 (replaced) [pdf, other]
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Title: Structural and electronic properties of the pure and stable elemental 3D topological Dirac semimetal $α$-SnAuthors: Ivan Madarevic, Umamahesh Thupakula, Gertjan Lippertz, Niels Claessens, Pin-Cheng Lin, Harsh Bana, Giovanni Di Santo, Sara Gonzalez, Luca Petaccia, Maya Narayanan Nair, Lino M.C. Pereira, Chris Van Haesendonck, Margriet Van BaelComments: APM19-AR-01221RSubjects: Materials Science (cond-mat.mtrl-sci)
In-plane compressively strained $\alpha$-Sn films have been theoretically predicted and experimentally proven to possess non-trivial electronic states of a 3D topological Dirac semimetal. The robustness of these states typically strongly depends on purity, homogeneity and stability of the grown material itself. By developing a reliable fabrication process, we were able to grow pure strained $\alpha$-Sn films on InSb(100), without heating of the substrate during growth, nor using any dopants. The $\alpha$-Sn films were grown by molecular beam epitaxy, followed by experimental verification of the achieved chemical purity and structural properties of the film's surface. Local insight into the surface morphology was provided by scanning tunneling microscopy. We detected the existence of compressive strain using M\"ossbauer spectroscopy and we observed a remarkable robustness of the grown samples against ambient conditions. The topological character of the samples was confirmed by angle-resolved photoemission spectroscopy, revealing the Dirac cone of the topological surface state. Scanning tunneling spectroscopy, moreover, allowed obtaining an improved insight into the electronic structure of the 3D topological Dirac semimetal $\alpha$-Sn above the Fermi level.
- arXiv:1912.07923 (replaced) [pdf]
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Title: Decorated dislocations against phonon propagation for thermal managementAuthors: Stefanos Giaremis, Joseph Kioseoglou, Mykola Isaiev, Imad Belabbas, Philomela Komninou, Konstantinos TermentzidisSubjects: Materials Science (cond-mat.mtrl-sci)
The impact of decorated dislocations on the effective thermal conductivity of GaN is investigated by means of equilibrium molecular dynamics simulations via the Green-Kubo approach. The formation of "nanowires" by a few atoms of In in the core of dislocations in wurtzite GaN is found to affect the thermal properties of the material, as it leads to a significant decrease of the thermal conductivity, along with an enhancement of its anisotropic character. The thermal conductivity of In-decorated dislocations is compared to the ones of pristine GaN, InN, and random and ordered InxGa1-xN alloy, to examine the impact of doping. Results are explained by the stress maps, the bonding properties and the phonon density of states of the aforementioned systems. The decorated dislocations engineering is a novel way to tune, among other transport properties, the effective thermal conductivity of materials at the nanoscale, which can lead to the manufacturing of interesting candidates for thermoelectric or anisotropic thermal dissipation devices.
- arXiv:1912.08379 (replaced) [pdf, other]
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Title: CASSCF with Extremely Large Active Spaces using the Adaptive Sampling Configuration Interaction MethodAuthors: Daniel S. Levine, Diptarka Hait, Norm M. Tubman, Susi Lehtola, K. Birgitta Whaley, Martin Head-GordonComments: 44 pages, 5 figuresSubjects: Computational Physics (physics.comp-ph); Strongly Correlated Electrons (cond-mat.str-el); Atomic and Molecular Clusters (physics.atm-clus); Chemical Physics (physics.chem-ph); Quantum Physics (quant-ph)
The complete active space self-consistent field (CASSCF) method is the principal approach employed for studying strongly correlated systems. However, exact CASSCF can only be performed on small active spaces of ~20 electrons in ~20 orbitals due to exponential growth in the computational cost. We show that employing the Adaptive Sampling Configuration Interaction (ASCI) method as an approximate Full CI solver in the active space allows CASSCF-like calculations within chemical accuracy (<1 kcal/mol for relative energies) in active spaces with more than ~50 active electrons in ~50 active orbitals, significantly increasing the sizes of systems amenable to accurate multiconfigurational treatment. The main challenge with using any selected CI-based approximate CASSCF is the orbital optimization problem; they tend to exhibit large numbers of local minima in orbital space due to their lack of invariance to active-active rotations (in addition to the local minima that exist in exact CASSCF). We highlight methods that can avoid spurious local extrema as a practical solution to the orbital optimization problem. We employ ASCI-SCF to demonstrate lack of polyradical character in moderately sized periacenes with up to 52 correlated electrons and compare against heat-bath CI on an iron porphyrin system with more than 40 correlated electrons.
- arXiv:2002.08137 (replaced) [pdf, ps, other]
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Title: Temporal relaxation of gapped many-body quantum systemsComments: 9 pages, 5 figures. Accepted for publication in Phys. Rev. BJournal-ref: Phys. Rev. B 101, 094302 (2020)Subjects: Statistical Mechanics (cond-mat.stat-mech)
Typicality of the orthogonal dynamics (TOD) is established as a generic feature of temporal relaxation processes in isolated many-body quantum systems. The basic idea in the simplest case is that the transient non-equilibrium behavior is mainly governed by the component of the time-evolved system state parallel to the initial state, while the orthogonal component appears as equilibrated right from the beginning. The main emphasis is laid on the largely unexplored and particularly challenging case that one energy level exhibits a much larger population than all the others. Important examples are gapped many-body systems at low energies, for instance due to a quantum quench. A general analytical prediction is derived and is found to compare very well with various numerically exact results.
- arXiv:2002.09299 (replaced) [pdf, other]
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Title: Ultrafast dynamics of the low frequency shear mode in $\mathrm{1T'-MoTe_2}$Comments: 5 pages, 4 figures, accepted for Applied Physics LettersJournal-ref: Applied Physics Letters, 116, 093103, 2020Subjects: Materials Science (cond-mat.mtrl-sci); Applied Physics (physics.app-ph)
We report on the dynamics of coherent phonons in semimetal 1T'-MoTe2 using femtosecond pump-probe spectroscopy. On an ultrafast sub-picosecond time scale at room temperature, a low frequency and long-lifetime shear phonon mode was observed at 0.39 THz, which was previously reported in the form of a characteristic phonon only in the low temperature Td-MoTe2 phase. Unlike the other optical phonon modes, the shear phonon mode was found to strongly couple with photoexcited carriers. Moreover, the amplitude of the shear mode surprisingly decreased with increasing excitation density, a phenomenon which can be attributed to be a consequence of the lattice temperature rising after excitation. These results provide useful physical information on ultrafast lattice symmetry switching between the normal semimetal 1T' and the lattice inversion symmetry breaking Type-II Weyl semimetal Td phases.
Crosses
- arXiv:1810.04647 (cross-list from cond-mat.mtrl-sci) [pdf, other]
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Title: Grain Boundary Shear Coupling is Not a Grain Boundary PropertySubjects: Materials Science (cond-mat.mtrl-sci); Statistical Mechanics (cond-mat.stat-mech)
Shear coupling implies that all grain boundary (GB) migration necessarily creates mechanical stresses/strains and is a key component to the evolution of all polycrystalline microstructures. We present MD simulation data and theoretical analyses that demonstrate the GB shear coupling is not an intrinsic GB property, but rather strongly depends on the type and magnitude of the driving force for migration and temperature. We resolve this apparent paradox by proposing a microscopic theory for GB migration that is based upon a statistical ensemble of line defects (disconnections) that are constrained to lie in the GB. Comparison with the MD results for several GBs provides quantitative validation of the theory as a function of stress, chemical potential jump and temperature.
- arXiv:1909.02633 (cross-list from physics.atom-ph) [pdf, other]
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Title: Direct observation of a highly forbidden optical transition in Sm:SrF$_2$Comments: 5 pages, 6 FiguresJournal-ref: Phys. Rev. A 100, 032502 (2019)Subjects: Atomic Physics (physics.atom-ph); Other Condensed Matter (cond-mat.other)
The $4f^6$ $^{7}F_0$ $\to 4f^6$ $^{5}D_0$ intra-configuration transition in Sm:SrF$_2$ is forbidden for Sm$^{2+}$ ions in the octahedrally symmetric substitution sites in SrF$_2$. We report the direct observation of this transition using laser-induced fluorescence at cryogenic temperatures, and measurements of the excited state lifetime and the excitation cross section. To the best of our knowledge, this optical transition has the longest lived excited state ever observed in a solid.
Tue, 10 Mar 2020
- arXiv:2003.03370 [pdf, other]
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Title: Solution to the modified Helmholtz equation for arbitrary periodic charge densitiesAuthors: Miriam Hinzen (1, 2, 3), Edoardo Di Napoli (1, 2), Daniel Wortmann (1, 3), Stefan Blügel (1, 3) ((1) IAS-1, Forschungszentrum Jülich and JARA-CSD, Jülich, (2) JSC, Forschungszentrum Jülich, (3) PGI-1, Forschungszentrum Jülich)Comments: submitted to the Journal of Mathematical PhysicsSubjects: Computational Physics (physics.comp-ph); Materials Science (cond-mat.mtrl-sci); Mathematical Physics (math-ph)
We present a general method for solving the modified Helmholtz equation without shape approximation for an arbitrary periodic charge distribution, whose solution is known as the Yukawa potential or the screened Coulomb potential. The method is an extension of Weinert's pseudo-charge method [M. Weinert, J. Math. Phys. 22, 2433 (1981)] for solving the Poisson equation for the same class of charge density distributions. The inherent differences between the Poisson and the modified Helmholtz equation are in their respective radial solutions. These are polynomial functions, for the Poisson equation, and modified spherical Bessel functions, for the modified Helmholtz equation. This leads to a definition of a modified pseudo-charge density and modified multipole moments. We have shown that Weinert's convergence analysis of an absolutely and uniformly convergent Fourier series of the pseudo-charge density is transferred to the modified pseudo-charge density. We conclude by illustrating the algorithmic changes necessary to turn an available implementation of the Poisson solver into a solver for the modified Helmholtz equation.
- arXiv:2003.03374 [pdf, other]
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Title: Theoretical investigation of antiferromagnetic skyrmions in a triangular monolayerSubjects: Materials Science (cond-mat.mtrl-sci)
The chiral spin textures of a two-dimensional (2D) triangular system, where both antiferromagnetic (AF) Heisenberg exchange and chiral Dzyaloshinsky-Moriya interactions co-exist, are investigated numerically with an optimized quantum Monte Carlo method based on mean-field theory. We find that: helical, skyrmionic and vortical AF crystals can be formed when an external magnetic field is applied perpendicular to the 2D monolayer; the sizes of these skyrmions and vortices change abruptly at several critical points of the external magnetic field; each of these AF crystals can be decomposed into three periodical ferromagnetic (FM) sublattices. The quantum ingredient implemented into the theoeretical framework helps to track the existence of AF skyrmion lattices down to low temperatures.
- arXiv:2003.03405 [pdf, other]
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Title: Deconstructing effective non-Hermitian dynamics in quadratic bosonic HamiltoniansComments: 28+7 pages, 10 figures, uses iopart.clsSubjects: Quantum Physics (quant-ph); Statistical Mechanics (cond-mat.stat-mech)
Unlike their fermionic counterparts, the dynamics of Hermitian quadratic bosonic Hamiltonians are governed by a generally non-Hermitian Bogoliubov-de Gennes effective Hamiltonian. This underlying non-Hermiticity gives rise to a dynamically stable regime, whereby all observables undergo bounded evolution in time, and a dynamically unstable one, whereby evolution is unbounded for at least some observables. We show that stability-to-instability transitions may be classified in terms of a suitably generalized $\mathcal{P}\mathcal{T}$ symmetry, which can be broken when diagonalizability is lost at exceptional points in parameter space, but also when degenerate real eigenvalues split off the real axis while the system remains diagonalizable. By leveraging tools from Krein stability theory in indefinite inner-product spaces, we introduce an indicator of stability phase transitions, which naturally extends the notion of phase rigidity from non-Hermitian quantum mechanics to the bosonic setting. As a paradigmatic example, we fully characterize the stability phase diagram of a bosonic analogue to the Kitaev-Majorana chain under a wide class of boundary conditions. In particular, we establish a connection between phase-dependent transport properties and the onset of instability, and argue that stable regions in parameter space become of measure zero in the thermodynamic limit. Our analysis also reveals that boundary conditions that support Majorana zero modes in the fermionic Kitaev chain are precisely the same that support stability in the bosonic chain.
- arXiv:2003.03408 [pdf, other]
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Title: Compensated Quantum and Topological Hall Effects of Electrons in Polyatomic Stripe LatticesComments: 12 pages, 15 figuresJournal-ref: Phys. Status Solidi B 1900518 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
The quantum Hall effect is generally understood for free electron gases, in which topologically protected edge states between Landau levels (LLs) form conducting channels at the edge of the sample. In periodic crystals, the LLs are imprinted with lattice properties; plateaus in the transverse Hall conductivity are not equidistant in energy anymore. Herein, crystals with a polyatomic basis are considered. For a stripe arrangement of different atoms, the band structure resorts nontrivially and exhibits strong oscillations that form a salient pattern with very small bandgaps. The Hall conductivity strongly decreases for energies within these bands, and only sharp peaks remain for energies in the gap. These effects are traced back to open orbits in the initial band structure; the corresponding LLs are formed from states with positive and negative effective mass. The partial cancellation of transverse charge conductivity also holds for different polyatomic stripe lattices and even when the magnetic field is replaced by a topologically nontrivial spin texture. The topological Hall effect is suppressed in the presence of magnetic skyrmions. The discussion is complemented by calculations of Hofstadter butterflies and orbital magnetization.
- arXiv:2003.03415 [pdf, other]
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Title: Large deviations of connected components in the stochastic block modelComments: 8 pages, 7 figuresSubjects: Physics and Society (physics.soc-ph); Disordered Systems and Neural Networks (cond-mat.dis-nn)
We study the stochastic block model which is often used to model community structures and study community-detection algorithms. We consider the case of two blocks in regard to its largest connected component and largest bicomponent, respectively. We are especially interested in the distributions of their sizes including the tails down to probabilities smaller than $10^{-800}$. For this purpose we use sophisticated Markov chain Monte Carlo simulations to sample graphs from the stochastic block model ensemble. We use this data to study the large-deviation rate function and conjecture that the large-deviation principle holds. Further we compare the distribution to the well known Erd\H{o}s-R\'{e}nyi ensemble, where we notice subtle differences at and above the percolation threshold, near the community detection threshold.
- arXiv:2003.03416 [pdf, other]
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Title: Interplay of exchange and superexchange in triple quantum dotsSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Quantum Physics (quant-ph)
Recent experiments on semiconductor quantum dots have demonstrated the ability to utilize a large quantum dot to mediate superexchange interactions and generate entanglement between distant spins. This opens up a possible mechanism for selectively coupling pairs of remote spins in a larger network of quantum dots. Taking advantage of this opportunity requires a deeper understanding of how to control superexchange interactions in these systems. Here, we consider a triple-dot system arranged in linear and triangular geometries. We use configuration interaction calculations to investigate the interplay of superexchange and nearest-neighbor exchange interactions as the location, detuning, and electron number of the mediating dot are varied. We show that superexchange processes strongly enhance and increase the range of the net spin-spin exchange as the dots approach a linear configuration. Furthermore, we show that the strength of the exchange interaction depends sensitively on the number of electrons in the mediator. Our results can be used as a guide to assist further experimental efforts towards scaling up to larger, two-dimensional quantum dot arrays.
- arXiv:2003.03421 [pdf, other]
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Title: Disorder-induced rippled phases and multicriticality in free-standing grapheneComments: 4+5 pages, 9 figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Statistical Mechanics (cond-mat.stat-mech)
One of the most exciting phenomena observed in crystalline disordered membranes, including a suspended graphene, is rippling, i.e. a formation of static flexural deformations. Despite an active research, it still remains unclear whether the rippled phase exists in the thermodynamic limit, or it is destroyed by thermal fluctuations. We demonstrate that a sufficiently strong short-range disorder stabilizes ripples, whereas in the case of a weak disorder the thermal flexural fluctuations dominate in the thermodynamic limit. The phase diagram of the disordered suspended graphene contains two separatrices: the crumpling transition line dividing the flat and crumpled phases and the rippling transition line demarking the rippled and clean phases. At the intersection of the separatrices there is the unstable, multicritical point which splits up all four phases. Most remarkably, rippled and clean flat phases are described by a single stable fixed point which belongs to the rippling transition line. Coexistence of two flat phases in the single point is possible due to non-analiticity in corresponding renormalization group equations and reflects non-commutativity of limits of vanishing thermal and rippling fluctuations.
- arXiv:2003.03422 [pdf]
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Title: Corner states and topological transitions in two-dimensional higher-order topological sonic crystals with inversion symmetryAuthors: Zhan Xiong, Zhi-Kang Lin, Hai-Xiao Wang, Xiujuan Zhang, Ming-Hui Lu, Yan-Feng Chen, Jian-Hua JiangSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci)
Macroscopic two-dimensional sonic crystals with inversion symmetry are studied to reveal higher-order topological physics in classical wave systems. By tuning a single geometry parameter, the band topology of the bulk and the edges can be controlled simultaneously. The bulk band gap forms an acoustic analog of topological crystalline insulators with edge states which are gapped due to symmetry reduction on the edges. In the presence of mirror symmetry, the band topology of the edge states can be characterized by the Zak phase, illustrating the band topology in a hierarchy of dimensions, which is at the heart of higher-order topology. Moreover, the edge band gap can be closed without closing the bulk band gap, revealing an independent topological transition on the edges. The rich topological transitions in both bulk and edges can be well-described by the symmetry eigenvalues at the high-symmetry points in the bulk and surface Brillouin zones. We further analyze the higher-order topology in the shrunken sonic crystals where slightly different physics but richer corner and edge phenomena are revealed. In these systems, the rich, multidimensional topological transitions can be exploited for topological transfer among zero-, one- and two- dimensional acoustic modes by controlling the geometry.
- arXiv:2003.03425 [pdf, other]
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Title: Particles and intrinsic fields supporting topological thermoelectricityComments: 24 pages, 4 figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
At present, topological insulators are the most efficient thermoelectric materials at room temperature. However, at non-zero temperatures, it seems to arise a conflict between having time-reversal symmetry, which implies minimal entropy, and the Seebeck coefficient, which is the entropy carried by each electric charge unit. This has obliged us to analyze the mathematical and physical background taking into account relativistic phonons besides the electrons within quantum field theory. In this search, we found an approximate expression for the intrinsic topological field b in terms of the Chern number, the Fermi velocity $v_F$ and the electron effective mass $m$, which allows to connect the topologically non-trivial insulator with the trivial one, being consistent with their topological properties and physical robustness. Thanks to this, we demonstrate that for three-dimensional topological insulators in thin-film conditions, among others, phonons have chirality coupling in a novel way to electron dynamics which preserves time-reversal symmetry. This explains the compatibility of the thermoelectricity within topological insulators and shows explicitly how it adapts to the family of topological insulators Bi$_2$Se$_3$.
- arXiv:2003.03430 [pdf, other]
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Title: Photon-mediated charge-exchange reactions between 39K atoms and 40Ca+ ions in a hybrid trapAuthors: Hui Li, S. Jyothi, Ming Li, Jacek Klos, Alexander Petrov, Kenneth R Brown, Svetlana KotochigovaComments: 13 pages, 16 figuresJournal-ref: Phys. Chem. Chem. Phys., 2020,22, 10870-10881Subjects: Atomic Physics (physics.atom-ph); Quantum Gases (cond-mat.quant-gas)
We present experimental evidence of charge exchange between laser-cooled potassium $^{39}$K atoms and calcium $^{40}$Ca$^+$ ions in a hybrid atom-ion trap and give quantitative theoretical explanations for the observations. The $^{39}$K atoms and $^{40}$Ca$^+$ ions are held in a magneto-optical (MOT) and a linear Paul trap, respectively. Fluorescence detection and high resolution time of flight mass spectra for both species are used to determine the remaining number of $^{40}$Ca$^+$ ions, the increasing number of $^{39}$K$^+$ ions, and $^{39}$K number density as functions of time. Simultaneous trap operation is guaranteed by alternating periods of MOT and $^{40}$Ca$^+$ cooling lights, thus avoiding direct ionization of $^{39}$K by the $^{40}$Ca$^+$ cooling light. We show that the K-Ca$^+$ charge-exchange rate coefficient increases linearly from zero with $^{39}$K number density and, surprisingly, the fraction of $^{40}$Ca$^+$ ions in the 4p\,$^2$P$_{1/2}$ electronically-excited state. Combined with our theoretical analysis, we conclude that these data can only be explained by a process that starts with a potassium atom in its electronic ground state and a calcium ion in its excited 4p\,$^2$P$_{1/2}$ state producing ground-state $^{39}$K$^+$ ions and metastable, neutral Ca\,(3d4p$^3$P$_1$) atoms, releasing only 150 cm$^{-1}$ equivalent relative kinetic energy. Charge-exchange between either ground- or excited-state $^{39}$K and ground-state $^{40}$Ca$^+$ is negligibly small as no energetically-favorable product states are available. Our experimental and theoretical rate coefficients of $9\times10^{-10}$ cm$^3$/s are in agreement given the uncertainty budgets.
- arXiv:2003.03439 [pdf, other]
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Title: Topological surface states of MnBi$_2$Te$_4$ at finite temperatures and at domain wallsComments: 6 pages main text, 7 supplementalSubjects: Materials Science (cond-mat.mtrl-sci); Strongly Correlated Electrons (cond-mat.str-el)
MnBi$_2$Te$_4$ has recently been the subject of intensive study, due to the prediction of axion insulator, Weyl semimetal, and quantum anomalous Hall insulator phases, depending on the structure and magnetic ordering. Experimental results have confirmed some aspects of this picture, but several experiments have seen zero-gap surfaces states at low temperature, in conflict with expectations. In this work, we develop a first-principles-based tight-binding model that allows for arbitrary control of the local spin direction and spin-orbit coupling, enabling us to accurately treat large unit-cells. Using this model, we examine the behavior of the topological surface state as a function of temperature, finding a gap closure only above the N\'eel temperature. In addition, we examine the effect of magnetic domains on the electronic structure, and we find that the domain wall zero-gap states extend over many unit-cells. These domain wall states can appear similar to the high temperature topological surface state when many domain sizes are averaged, potentially reconciling theoretical results with experiments.
- arXiv:2003.03443 [pdf, ps, other]
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Title: Anodic Decomposition of Surface Films on High Voltage Spinel Surfaces -- Density Function Theory and Experimental StudyComments: 8 figuresJournal-ref: Journal of Chemical Physics volume 151, article 234713 (2019)Subjects: Materials Science (cond-mat.mtrl-sci); Chemical Physics (physics.chem-ph)
Oxidative decomposition of organic-solvent-based liquid electrolytes at cathode material interfaces has been identified as a main reason for rapid capacity fade in high-voltage lithium ion batteries. The evolution of "cathode electrolyte interphase: (CEI) films, partly or completely consisting of electrolyte decomposition products, has also recently been demonstrated to be correlated with battery cycling behavior at high potentials. Using Density Functional Theory (DFT) calculations, the hybrid PBE0 functional, and the (001) surfaces of spinel oxides as models, we examine these two interrelated processes. Consistent with previous calculations, ethylene carbonate (EC) solvent molecules are predicted to be readily oxidized on the Li(x)Mn(2)O(4) (001) surface at modest operational voltages, forming adsorbed organic fragments. Further oxidative decompostion of such CEI fragments to release CO2 gas is however predicted to require higher voltages consistent with Li(x)Ni(0.5)Mn(1.5)O(4) (LNMO) at smaller x values. We argue that multi-step reactions, involving first formation of CEI films and then further oxidization of CEI at higher potentials, are most relevant to capacity fade. Mechanisms associated with dissolution or oxidation of native Li2CO3 films, which is removed before the electrolyte is in contact with oxide surfaces, are also explored.
- arXiv:2003.03448 [pdf]
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Title: Strengthening the magnetic interactions in pseudobinary first-row transition metal thiocyanates, $\it{M}$(NCS)$_{2}$Authors: Euan N. Bassey, Joseph A. M. Paddison, Evan N. Keyzer, Jeongjae Lee, Pascal Manuel, Ivan da Silva, Siân E. Dutton, Clare P. Grey, Matthew J. CliffeComments: 17 pages, 10 figuresSubjects: Materials Science (cond-mat.mtrl-sci); Strongly Correlated Electrons (cond-mat.str-el)
Understanding the effect of chemical composition on the strength of magnetic interactions is key to the design of magnets with stronger exchange interactions. The magnetic divalent first-row transition metal (TM) thiocyanates are a class of chemically simple layered molecular frameworks. Here, we report two new members of the family, manganese (II) thiocyanate, Mn(NCS)$_{2}$, and iron (II) thiocyanate, Fe(NCS)$_{2}$. Using magnetic susceptibility measurements on these materials and on cobalt (II) thiocyanate and nickel (II) thiocyanate, Co(NCS)$_{2}$ and Ni(NCS)$_{2}$, respectively, we identify significantly stronger net antiferromagnetic interactions between the earlier TM ions-a decrease in the Weiss constant, \theta, from 29 K for Ni(NCS)$_{2}$ to -115 K for Mn(NCS)$_{2}$-a consequence of more diffuse 3d orbitals, increased orbital overlap and increasing numbers of unpaired $\it{t}$$_{2g}$ electrons. We elucidate the magnetic structures of these materials: Mn(NCS)$_{2}$, Fe(NCS)$_{2}$ and Co(NCS)$_{2}$ order into the same antiferromagnetic commensurate ground state, whilst Ni(NCS)$_{2}$ adopts a ground state structure consisting of ferromagnetically ordered layers stacked antiferromagnetically. We show that magnetic molecular frameworks with significantly stronger net exchange interactions can be constructed by using earlier TMs.
- arXiv:2003.03457 [pdf, other]
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Title: Direct and High-Throughput Fabrication of Mie-Resonant Metasurfaces via Single-Pulse Laser InterferenceAuthors: Jonas Berzinš, Simonas Indrišiūnas, Koen van Erve, Arvind Nagarajan, Stefan Fasold, Michael Steinert, Giampiero Gerini, Paulius Gečys, Thomas Pertsch, Stefan M. B. Bäumer, Frank SetzpfandtJournal-ref: ACS Nano (2020)Subjects: Optics (physics.optics); Materials Science (cond-mat.mtrl-sci); Applied Physics (physics.app-ph)
High-index dielectric metasurfaces featuring Mie-type electric and magnetic resonances have been of a great interest in a variety of applications such as imaging, sensing, photovoltaics and others, which led to the necessity of an efficient large-scale fabrication technique. To address this, here we demonstrate the use of single-pulse laser interference for direct patterning of an amorphous silicon film into an array of Mie resonators. The proposed technique is based on laser-interference-induced dewetting. A precise control of the laser pulse energy enables the fabrication of ordered dielectric metasurfaces in areas spanning tens of micrometers and consisting of thousands of hemispherical nanoparticles with a single laser shot. The fabricated nanoparticles exhibit a wavelength-dependent optical response with a strong electric dipole signature. Variation of the pre-deposited silicon film thickness allows tailoring of the resonances in the targeted visible and infrared spectral ranges. Such direct and high-throughput fabrication paves the way towards a simple realization of spatially invariant metasurface-based devices.
- arXiv:2003.03458 [pdf, ps, other]
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Title: Mössbauer parameters of $^{57}$Fe substituents in the topological insulator $Bi_2Se_3$Authors: Jorge H. RodriguezSubjects: Strongly Correlated Electrons (cond-mat.str-el)
$^{57}$Fe M\"ossbauer spectroscopy can probe several \emph{local} structural, electronic and magnetic properties of Fe-containing systems. However, to establish a direct relationship between these properties and a system's geometric structure, the experimental M\"ossbauer parameters need to be analyzed \emph{via} electronic structure calculations. Herein, structural, electronic and magnetic effects of iron substituents in the topological insulator $Bi_2Se_3$, as uniquely probed by $^{57}$Fe M\"ossbauer spectroscopy, have been determined \emph{via} spin-polarized electronic structure calculations. The iron ion substituents, of \emph{nominal} Fe$^{3+}(S = 5/2)$ oxidation and spin state, are unequivocally shown to substitute Bi$^{3+}$ sites in epitaxial $Bi_2Se_3$ thin-films used for M\"ossbauer measurements. Concomitant with iron substitution, \emph{localized} structural rearrangements take place whereby the longer Bi-Se bonds of the native system are replaced by significantly shorter Fe-Se counterparts in the Fe-containing system. The resulting distorted-octahedral environment about substituent iron ions gives rise to characteristic M\"ossbauer parameters ($\delta_{Fe} \approx$ 0.51 mm/s, $\Delta E_{Q} \approx$ 0.20 mm/s) which have been calculated in excellent agreement with measured values for Fe-doped $Bi_2Se_3$ thin films. Consistent with a substituent Fe$^{3+}$ ion's \emph{nominal} high-spin electronic configuration ($t_{2g}^{\uparrow \uparrow \uparrow} e_g^{\uparrow \uparrow}$), an Fe-centered spin density has been established which, nevertheless, extends towards neighboring Se atoms \emph{via} direct Fe-Se bonding and concomitant Fe(d)-Se(p) hybridization.
- arXiv:2003.03476 [pdf, ps, other]
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Title: Time Scales for Rounding of Rocks through Stochastic ChippingAuthors: D. J. Priour JrComments: 19 pages, 27 figuresSubjects: Statistical Mechanics (cond-mat.stat-mech); Soft Condensed Matter (cond-mat.soft)
For 3D geometries, we consider stones (modeled as convex polyhedra) subject to weathering with planar slices of random orientation and depth successively removing material, ultimately yielding smooth and round (i.e. spherical) shapes. An exponentially decaying acceptance probability in the area exposed by a prospective slice provides a stochastically driven physical basis for the removal of material in fracture events. With a variety of quantitative measures, in steady state we find a power law decay of deviations in a toughness parameter $\gamma$ from a perfect spherical shape. We examine the time evolution of shapes for stones initially in the form of cubes as well as irregular fragments created by cleaving a regular solid many times along random fracture planes. In the case of the former, we find two sets of second order structural phase transitions with the usual hallmarks of critical behavior. The first involves the simultaneous loss of facets original to the parent solid, while the second of these involves a shift to a spherical profile. Nevertheless, for mono-dispersed irregular solids, the loss of primordial facets is not simultaneous but occurs in stages. In the case of initially irregular stones, strong disorder obscures individual structural transitions, and relevant observables are smooth with respect to time. More broadly, we find that salient times scale quadratically in $\gamma$. We use the universal dependence of variables on the volume remaining to calculate time dependent variables for a variety of erosion scenarios with results from a single weathering scheme such as the case in which the fracture acceptance probability depends on the relative area of the prospective new face. We calculate time scales for the attainment of structural milestones, obtaining a closed form approximate expression which bounds direct simulation results from above.
- arXiv:2003.03521 [pdf, other]
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Title: Apical oxygen vibrations dominant role in cuprate superconductivity and its interplay with spin fluctuationsSubjects: Superconductivity (cond-mat.supr-con)
Microscopic theory of a high temperature cuprate Bi2212 based on main pairing channel of electrons in CuO planes due to lateral vibrations of the apical oxygen atoms in adjacent the SrO ionic insulator layer is proposed. Similar ionic substrate phonon model was used recently to explain very high critical temperature in novel one unit cell FeSe on perovskite STO. A microscopic vibration theory identifies the 40 meV phonon mode coupled to conducting CuO planes with electron-electron strength 0.5. It naturally explain the kink in dispersion relation observed by ARPES and the and effect of the isotope substitution. To describe the pseudogap physics by a single band fourfold symmetric t-t' Hubbard model, the hopping parameters t'=-0.184 and the on side repulsion energy U=1.9t are chosen. The electronic system is still strongly correlated, but U is weak enough to be effectively described by the mean field model and its perturbative extensions. In particular the fragmentation of the Fermi surface in underdoped samples and the non-circularity of the Fermi Surface are described well within the "symmetrized Hartree - Fock" approximation. The T star transition line dividing the pseudogap (locally antiferromagnetic) and paramagnetic phases and susceptibility (describing spin fluctuations coupling to 2DEG) are also obtained within this approximation. The superconducting gap was calculated in the framework of the weak coupling approximation for both the phonon and the spin fluctuations channels. The dominant "glue" responsible for the d - wave pairing is the phonon mode rather than spin fluctuations, although the later enhances superconductivity by 10-15%. The dependence of the superconducting gap and certain normal state properties, like the kink in dispertion relation,on doping, temperature and effect of the oxygen isotope substitution are obtained.
- arXiv:2003.03529 [pdf]
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Title: A Study of Selectively Digital Etching Silicon-Germanium with Nitric and Hydrofluoric AcidsAuthors: Chen Li (1 and 2), Huilong Zhu (1, 2 and 3), Yongkui Zhang (1), Xiaogen Yin (1 and 2), Kunpeng Jia (1), Junjie Li (1), Guilei Wang (1), Zhenzhen Kong (1), Anyan Du (1), Tengzhi Yang (1 and 2), Liheng Zhao (1 and 3), Lu Xie (1 and 2), Xuezheng Ai (1), Shishuai Ma (1), Yangyang Li (1 and 2), Henry H. Radamson (1 and 2) Chen Li (1 and 2), Huilong Zhu (1, 2 and 3), Yongkui Zhang (1), Xiaogen Yin (1 and 2), Kunpeng Jia (1), Junjie Li (1), Guilei Wang (1), Zhenzhen Kong (1), Anyan Du (1), Tengzhi Yang (1 and 2), Liheng Zhao (1 and 3), Lu Xie (1 and 2), Xuezheng Ai (1), Shishuai Ma (1), Yangyang Li (1 and 2), Henry H. Radamson (1 and 2) ((1) Key Laboratory of Microelectronics Devices and Integrated Technology, Institute of Microelectronics, Chinese Academy of Sciences. (2) University of Chinese Academy of Sciences. (3) University of Science and Technology of China.)Comments: 19 pages, 9 figuresSubjects: Applied Physics (physics.app-ph); Materials Science (cond-mat.mtrl-sci)
A digital etching method was proposed to achieve excellent control of etching depth. The digital etching characteristics of p+ Si and Si0.7Ge0.3 using the combinations of HNO3 oxidation and BOE oxide removal processes were studied. Experiments showed that oxidation saturates with time due to low activation energy. A physical model was presented to describe the wet oxidation process with nitric acid. The model was calibrated with experimental data and the oxidation saturation time, final oxide thickness, and selectivity between Si0.7Ge0.3 and p+ Si were obtained. The digital etch of laminated Si0.7Ge0.3/p+ Si was also investigated. The depth of the tunnels formed by etching SiGe layers between two Si layers was found in proportion to digital etching cycles. And oxidation would also saturate and the saturated relative etched amount per cycle (REPC) was 0.5 nm (4 monolayers). A corrected selectivity calculation formula was presented. The oxidation model was also calibrated with Si0.7Ge0.3/p+ Si stacks, and selectivity from model was the same with the corrected formula. The model can also be used to analyze process variations and repeatability. And it could act as a guidance for experiment design. Selectivity and repeatability should make a trade-off.
- arXiv:2003.03544 [pdf, other]
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Title: Tunability of electrical and thermoelectrical properties of monolayer MoS$_2$ through oxygen passivationAuthors: Swarup Deb, Pritam Bhattacharyya, Poulab Chakrabarti, Himadri Chakraborti, Kantimay Das Gupta, Alok Shukla, Subhabrata DharComments: 6 pages, 5 figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Electric and thermoelectric properties of strictly monolayer MoS$_2$ films, which are grown using a novel micro-cavity based CVD growth technique, have been studied under diverse environmental and annealing conditions. Resistance of a thermoelectric device that is fabricated on a continuous monolayer MoS$_2$ layer using photolithography technique has been found to reduce by about six orders of magnitudes upon annealing in vacuum at 525 K. Seebeck coefficient of the layer also reduces by almost an order of magnitude upon annealing. When the sample is exposed to oxygen atmosphere, these parameters return to their previous values. In fact, it has been found that the electron concentration, mobility as well as the thermoelectric power of the material can be tuned by controlling the temperature of annealing and oxygen exposure. Once established, these values are maintained as long as the layer is not exposed to oxygen environment. This can offer a unique way to control doping in the material provided an effective encapsulation method is devised. Such control is an important step forward for device application. The effect has been attributed to the passivation of di-sulfur vacancy donors present in the MoS$_2$ film by physisorbed oxygen molecules. Band structural calculations using density functional theory have been carried out, results of which indeed validate this picture.
- arXiv:2003.03555 [pdf, other]
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Title: Honeycomb Layered Oxides: Structure, Energy Storage, Transport, Topology and Relevant InsightsAuthors: Godwill Mbiti Kanyolo, Titus Masese, Nami Matsubara, Chih-Yao Chen, Josef Rizell, Ola Kenji Forslund, Elisabetta Nocerino, Konstantinos Papadopoulos, Anton Zubayer, Minami Kato, Kohei Tada, Keigo Kubota, Hiroshi Senoh, Zhen-Dong Huang, Yasmine Sassa, Martin Mansson, Hajime Matsumoto, Qiang XuComments: 53 pages, 21 figures, 1 table, review manuscriptSubjects: Materials Science (cond-mat.mtrl-sci)
The advent of nanotechnology has hurtled the discovery and development of nanostructured materials with stellar chemical and physical functionalities in a bid to address issues in energy, environment, telecommunications and healthcare. In this quest, honeycomb layered oxides have emerged as materials exhibiting fascinatingly rich crystal chemistry and play host to varied exotic electromagnetic and topological phenomena. These oxide materials, consisting mainly of alkali metal or coinage metal atoms sandwiched between slabs of transition metal atoms arranged in a honeycomb fashion, are of great utility and diverse interest in a multiple fields ranging from materials science, solid-state chemistry, electrochemistry to condensed matter physics. Currently, with a niche application in energy storage as high-voltage materials, the honeycomb layered oxides serve as ideal pedagogical exemplars of the innumerable capabilities of nanomaterials. In this Review, we delineate the relevant chemistry and physics of honeycomb layered oxides, and discuss their functionalities for tunable electrochemistry, superfast ionic conduction, optics, electromagnetism and topology. Moreover, we elucidate the unexplored albeit vastly promising crystal chemistry space whilst outlining effective ways to identify regions within this compositional space, particularly where interesting electromagnetic and topological properties could be lurking within the aforementioned alkali and coinage-metal honeycomb layered oxide structures. We conclude by pointing towards possible future research directions, particularly the prospective realisation of Kitaev-Heisenberg-Dzyaloshinskii-Moriya interactions with single crystals and Floquet theory in closely-related honeycomb layered oxide materials.
- arXiv:2003.03561 [pdf, other]
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Title: Simulation of nodal-line semimetal in amplitude-shaken optical latticesComments: 11 pages, 8 figuresSubjects: Quantum Gases (cond-mat.quant-gas); Quantum Physics (quant-ph)
With topologcial semimetal developing, semimetal with nodal-line ring comes into people's vision as a powerful candidate for practical application of topological devices. We propose a method using ultracold atoms in two-dimensional amplitude-shaken bipartite hexagonal optical lattice to simulate nodal-line semimetal, which can be achieved in experiment by attaching one triangular optical lattice to a hexangonal optical lattice and periodically modulating the intensity and position of the triangular lattice. By amplitude shaking, a time-reversal-symmetry-unstable mode is introduced into the bipartite optical lattice, and then the nodal-line semimetal is gotten by adjusting the proportion of such mode and the trivial mode of hexagonal lattice. Through calculating the energy spectrum of effective Hamiltonian, the transformation from Dirac semimetal to nodal-line semimetal in pace with changing shaking parameters is observed. We also study the change of Berry curvature and Berry phase in the transformation, which provides guidance on measuring the transformation in experiment. By analyzing the symmetry of the system, the emergence of the time-reversal-symmetry-unstable mode is researched. This proposal provides a way to research the pure nodal-line semimetal without the influence of other bands, which may contribute to the study of those unique features of surface states and bulk states of nodal-line semimetal.
- arXiv:2003.03577 [pdf]
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Title: Giant magnetic exchange coupling in rhombus-shaped nanographenes with zigzag peripheryAuthors: Shantanu Mishra, Xuelin Yao, Qiang Chen, Kristjan Eimre, Oliver Groening, Ricardo Ortiz, Marco Di Giovannantonio, Juan Carlos Sancho-Garcia, Joaquin Fernandez-Rossier, Carlo A. Pignedoli, Klaus Muellen, Pascal Ruffieux, Akimitsu Narita, Roman FaselComments: 4 figures plus supplementary informationSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Nanographenes with zigzag edges are predicted to manifest non-trivial pi-magnetism resulting from the interplay of hybridization of localized frontier states and Coulomb repulsion between valence electrons. This provides a chemically tunable platform to explore quantum magnetism at the nanoscale and opens avenues toward organic spintronics. The magnetic stability in nanographenes is thus far limited by the weak magnetic exchange coupling which remains below the room temperature thermal energy. Here, we report the synthesis of large rhombus-shaped nanographenes with zigzag periphery on gold and copper surfaces. Single-molecule scanning probe measurements unveil an emergent magnetic spin-singlet ground state with increasing nanographene size. The magnetic exchange coupling in the largest nanographene, determined by inelastic electron tunneling spectroscopy, exceeds 100 meV or 1160 K, which outclasses most inorganic nanomaterials and remarkably survives on a metal electrode.
- arXiv:2003.03582 [pdf, ps, other]
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Title: Onset of topological quantum chaos in strongly correlated electron systemsComments: 5 pages, 4 figures, supplementary material, typos correctedSubjects: Strongly Correlated Electrons (cond-mat.str-el)
We address manifestations of quantum chaos at temperatures $T$ far below the Debye temperature $T_D$ associated with the onset of classical behavior, effects that are well documented in experimental studies of strongly correlated electron systems. We attribute this unexpected phenomenon to spontaneous rearrangement of the conventional Landau state beyond a critical point at which the {\it topological} stability of this state breaks down, leading to the formation of an interaction-induced flat band adjacent to the nominal Fermi surface. We demonstrate that beyond the critical point, the quasiparticle picture of such correlated Fermi systems still holds, since the damping of single-particle excitations remains small compared with the Fermi energy $T_F=p^2_F/2m_e$. A Pitaevskii-style equation for determination of the new quasiparticle momentum distribution $n_*({\bf p})$ is derived, which provides for explanation of the linear-in-$T$ behavior of the resistivity $\rho(T)$ found experimentally. The interplay between this scenario for non-Fermi-liquid behavior of $\rho(T)$ and an alternative picture based on the notion of Planckian dissipation is discussed.
- arXiv:2003.03587 [pdf, other]
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Title: Giant leaps and long excursions: fluctuation mechanisms in systems with long-range memoryComments: 5+5 pagesSubjects: Statistical Mechanics (cond-mat.stat-mech)
We analyse large deviations of time-averaged quantities in stochastic processes with long-range memory, where the dynamics at time t depends itself on the value q_t of the time-averaged quantity. First we consider the elephant random walk and a Gaussian variant of this model, identifying two mechanisms for unusual fluctuation behaviour, which differ from the Markovian case. In particular, the memory can lead to large deviation principles with reduced speeds, and to non-analytic rate functions. We then explain how the mechanisms operating in these two models are generic for memory-dependent dynamics and show other examples including a non-Markovian symmetric exclusion process.
- arXiv:2003.03590 [pdf, other]
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Title: Quantum turbulence simulations using the Gross-Pitaevskii equation: high-performance computing and new numerical benchmarksAuthors: Michikazu Kobayashi, Philippe Parnaudeau, Francky Luddens, Corentin Lothode, Luminita Danaila, Marc Brachet, Ionut DanailaComments: 61 pages, 21 figuresSubjects: Fluid Dynamics (physics.flu-dyn); Other Condensed Matter (cond-mat.other); Numerical Analysis (math.NA)
This paper is concerned with the numerical investigation of Quantum Turbulence (QT) described by the Gross-Pitaevskii (GP) equation. Numerical simulations are performed using a parallel (MPI-OpenMP) code based on a pseudo-spectral spatial discretization and second order splitting for the time integration. We start by revisiting (in the framework of high-performance/high-accuracy computations) well-known GP-QT settings, based on the analogy with classical vortical flows: Taylor-Green (TG) vortices and Arnold-Beltrami-Childress (ABC) flow. Two new settings are suggested to build the initial condition for the QT simulation. They are based on the direct manipulation of the wave function by generating a smoothed random phase (SRP) field, or seeding random vortex rings (RVR) pairs. The new initial conditions have the advantage to be simpler to implement than the TG and ABC approaches, while generating statistically equivalent QT fields. Each of these four GP-QT settings is described in detail by defining corresponding benchmarks that could be used to validate/calibrate new GP codes. We offer a comprehensive description of the numerical and physical parameters of each benchmark. We analyze the results in detail and present values, spectra and structure functions of main quantities of interest (energy, helicity, etc.) that are useful to describe the turbulent flow. Some general features of QT are identified, despite the variety of initial states.
- arXiv:2003.03594 [pdf, ps, other]
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Title: Field-selective classical spin liquid and magnetization plateaus on kagome latticeComments: 7 pages, 7 figuresJournal-ref: J. Phys. Soc. Jpn. 89, 053708 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el); Materials Science (cond-mat.mtrl-sci); Statistical Mechanics (cond-mat.stat-mech)
We obtain a classical spin liquid (CSL) phase by applying a magnetic field in $J_1$-$J_2$-$J_3$ Ising model on a kagome lattice. As we proved in the previous study [Phys. Rev. Lett. {\bf 119}, 077207 (2017)], this model realizes one species of CSL, the hexamer CSL, at zero magnetic field, which consists of macroscopically degenerate spin configurations with mixed total magnetization, $M$. The magnetic field selects its subset, which can be mapped to a trimer covering of the dual lattice, and forms a magnetization plateau of $M=1/9$. In addition to this CSL, we find two other magnetization plateaus at $M=5/9$ and $17/27$, which are ascribed to the "multimer" superstructures on a dual lattice.
- arXiv:2003.03611 [pdf, other]
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Title: Plasmon-assisted two-photon absorption in a semiconductor quantum dot -- metallic nanoshell conjugateComments: 10 two-column pages, 7 figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Tho-photon absorption holds potential for many practical applications. We theoretically investigate the onset of this phenomenon in a semiconductor quantum dot -- metallic nanoshell conjugate subjected to a resonant CW excitation. Two-photon absorption in this system may occur in two ways: incoherent -- due to a consecutive ground-to-one-exciton-to-biexciton transition and coherent -- due to a coherent two-photon process, involving the direct ground-to-biexciton transition in the quantum dot. The presence of a nanoshell nearby a quantum dot gives rise to two principal effects: (i) -- renormalization of the applied field amplitude and (ii) -- renormalization of the resonance frequencies and radiative relaxation rates of the quantum dot, both depending on the the quantum dot level populations. We show that in the perturbative regime, when the excitonic levels are only slightly populated, each of these factors may give rise to either suppression or enhancement of the two-photon absorption. The complicated interplay of the two determines the final effect. Beyond the perturbative regime, it is found that the two-photon absorbtion experiences a drastic enhancement, which occurs independently of the type of excitation, either into the one-exciton resonance or into the two-photon resonance. Other features of the two-photon absorption of the conjugate, that emerge due to the nanoparticles coupling, are bistability and self-oscillations, having no analog in the two-photon absorption of an isolated quantum dot.
- arXiv:2003.03624 [pdf]
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Title: Improved sensitivity and quantification for ${}^{29}$Si NMR experiments on solids using UDEFT (Uniform Driven Equilibrium Fourier Transform)Journal-ref: Solid State Nucl. Magn. Reson. 2019 (100) 52-62Subjects: Materials Science (cond-mat.mtrl-sci); Chemical Physics (physics.chem-ph)
We demonstrate the possibility to use UDEFT (Uniform Driven Equilibrium Fourier Transform) technique in order to improve the sensitivity and the quantification of one-dimensional ${}^{29}$Si NMR experiments under Magic-Angle Spinning (MAS). We derive an analytical expression of the signal-to-noise ratios of UDEFT and single-pulse (SP) experiments subsuming the contributions of transient and steady-state regimes. Using numerical spin dynamics simulations and experiments on ${}^{29}$Si-enriched amorphous silica and borosilicate glass, we show that 59${}_{180}$298${}_{0}$59${}_{180}$ refocusing composite $\pi$-pulse and the adiabatic inversion using tanh/tan modulation improve the robustness of UDEFT technique to rf-inhomogeneity, offset, and chemical shift anisotropy. These pulses combined with a two-step phase cycling limit the pulse imperfections and the artifacts produced by stimulated echoes. The sensitivity of SP, UDEFT and CPMG (Carr-Purcell Meiboom-Gill) techniques are compared experimentally on functionalized and non-functionalized mesoporous silica. Furthermore, experiments on a flame retardant material prove that UDEFT technique provides a better quantification of ${}^{29}$Si sites with higher sensitivity than SP method.
- arXiv:2003.03684 [pdf, ps, other]
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Title: Time-periodic quantum states of weakly interacting bosons in a harmonic trapComments: 15 pagesSubjects: Quantum Gases (cond-mat.quant-gas); High Energy Physics - Theory (hep-th); Mathematical Physics (math-ph); Quantum Physics (quant-ph)
We consider identical quantum bosons with weak contact interactions in a two-dimensional isotropic harmonic trap, and focus on states at the Lowest Landau Level (LLL). At linear order in the coupling parameter $g$, we exploit the rich algebraic structure of the problem to give an explicit construction of a large family of quantum states with energies of the form $E_0+gE_1/4+O(g^2)$, where $E_0$ and $E_1$ are integers. As a result, any superposition of these states evolves periodically with a period of at most $8\pi/g$ until, at much longer time scales of order $1/g^2$, corrections to the energies of order $g^2$ become important and may upset this perfectly periodic behavior. We further construct coherent-like combinations of these states that naturally connect to classical dynamics in an appropriate regime, and explain how our findings relate to the known time-periodic features of the corresponding weakly nonlinear classical theory. We briefly comment on possible generalizations of our analysis to other numbers of spatial dimensions and other analogous physical systems.
- arXiv:2003.03694 [pdf, other]
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Title: Bandgap Control in Two-Dimensional Semiconductors via Coherent Doping of Plasmonic Hot ElectronsAuthors: Yu-Hui Chen, Ronnie R. Tamming, Kai Chen, Zhepeng Zhang, Yanfeng Zhang, Justin M. Hodgkiss, Richard J. Blaikie, Boyang Ding, Min QiuSubjects: Optics (physics.optics); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Quantum Physics (quant-ph)
Bandgap control is of central importance for semiconductor technologies. The traditional means of control is to dope the lattice chemically, electrically or optically with charge carriers. Here, we demonstrate for the first time a widely tunable bandgap (renormalisation up to 650 meV at room-temperature) in two-dimensional (2D) semiconductors by coherently doping the lattice with plasmonic hot electrons. In particular, we integrate tungsten-disulfide (WS$_2$) monolayers into a self-assembled plasmonic crystal, which enables coherent coupling between semiconductor excitons and plasmon resonances. Accompanying this process, the plasmon-induced hot electrons can repeatedly fill the WS$_2$ conduction band, leading to population inversion and a significant reconstruction in band structures and exciton relaxations. Our findings provide an innovative and effective measure to engineer optical responses of 2D semiconductors, allowing a great flexiblity in design and optimisation of photonic and optoelectronic devices.
- arXiv:2003.03698 [pdf, other]
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Title: A review of shaped colloidal particles in fluids: Anisotropy and chiralityComments: 60 pages, 17 figuresSubjects: Fluid Dynamics (physics.flu-dyn); Soft Condensed Matter (cond-mat.soft)
This review treats asymmetric colloidal particles moving through their host fluid under the action of some form of propulsion. The propulsion can come from an external body force or from external shear flow. It may also come from externally-induced stresses at the surface, arising from imposed chemical, thermal or electrical gradients. The resulting motion arises jointly from the driven particle and the displaced fluid. If the objects are asymmetric, every aspect of their motion and interaction depends on the orientation of the objects. This orientation in turn changes in response to the driving. The objects' shape can thus lead to a range of emergent anisotropic and chiral motion not possible with isotropic spherical particles. We first consider what aspects of a body's asymmetry can affect its drift through a fluid, especially chiral motion. We next discuss driving by injecting external force or torque into the particles. Then we consider driving without injecting force or torque. This includes driving by shear flow and driving by surface stresses, such as electrophoresis. We consider how time-dependent driving can induce collective orientational order and coherent motion. We show how a given particle shape can be represented using an assembly of point forces called a Stokeslet object. We next consider the interactions between anisotropic propelled particles, the symmetries governing the interactions, and the possibility of bound pairs of particles. Finally we show how the collective hydrodynamics of a suspension can be qualitatively altered by the particles' shapes. The asymmetric responses discussed here are broadly relevant also for swimming propulsion of active micron-scale objects such as microorganisms.
- arXiv:2003.03700 [pdf, other]
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Title: Dynamical Phase Transitions and their Relation to Thermodynamic Glass PhysicsSubjects: Statistical Mechanics (cond-mat.stat-mech); Soft Condensed Matter (cond-mat.soft)
We review recent developments in structural-dynamical phase transitions in trajectory space. An open question is how the dynamic facilitation theory of the glass transition may be reconciled with thermodynamic theories that posit a vanishing configurational entropy. Dynamic facilitation theory invokes a dynamical phase transition, between an active phase (close to the normal liquid) and an inactive phase which is glassy, whose order parameter is either dynamic or a time-averaged structural quantity. In particular, the dynamical phase transition in systems with non-trivial thermodynamics manifests signatures of a lower critical point, which lies close to the putative Kauzmann temperature, where any thermodynamic phase transition to an ideal glass state might occur. We discuss these findings, and suggest that the lower critical point of the structural-dynamical phase transition may be related to the large drop in configurational entropy that occurs in the inactive phase of the dynamical phase transition. Increasing supercooling thus brings configurational entropy of the normal liquid much lower, along with the temperature.
- arXiv:2003.03718 [pdf, other]
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Title: Influence of the velocity barrier on the massive Dirac electron transport in a monolayer MoS$_{2}$ quantum structureSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Using the transfer matrix method, spin- and valley-dependent electron transport properties modulated by the velocity barrier were studied in the normal/ferromagnetic/normal monolayer MoS$_{2}$ quantum structure. Based on Snell's Law in optics, we define the velocity barrier as $\xi=v_{2}/v_{1}$ by changing the Fermi velocity of the intermediate ferromagnetic region to obtain a deflection condition during the electron transport process in the structure. The results show that both the magnitude and the direction of spin- and valley-dependent electron polarization can be regulated by the velocity barrier. $-100\%$ polarization of spin- and valley-dependent electron can be achieved for $\xi>1$, while $100\%$ polarization can be obtained for $\xi<1$. Furthermore, it is determined that perfect spin and valley transport always occur at a large incident angle. In addition, the spin- and valley-dependent electron transport considerably depends on the length $k_{F}L$ and the gate voltage $U(x)$ of the intermediate ferromagnetic region. These findings provide an effective method for designing novel spin and valley electronic devices.
- arXiv:2003.03719 [pdf, ps, other]
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Title: Field-induced spin reorientation in the antiferromagnetic Dirac material EuMnBi$_2$ revealed by neutron and resonant x-ray diffractionAuthors: H. Masuda, H. Sakai, H. Takahashi, Y. Yamasaki, A. Nakao, T. Moyoshi, H. Nakao, Y. Murakami, T. Arima, S. IshiwataComments: 16 pages, 5 figures, accepted in PRBSubjects: Materials Science (cond-mat.mtrl-sci); Strongly Correlated Electrons (cond-mat.str-el)
Field-dependent magnetic structure of a layered Dirac material EuMnBi$_2$ was investigated in detail by the single crystal neutron diffraction and the resonant x-ray magnetic diffraction techniques. On the basis of the reflection conditions in the antiferromagnetic phase at zero field, the Eu moments were found to be ordered ferromagnetically within the $ab$ plane and stacked antiferromagnetically along the $c$ axis in the sequence of up-up-down-down. Upon the spin-flop transition under the magnetic field parallel to the $c$ axis, the Eu moments are reoriented from the $c$ to the $a$ or $b$ directions forming two kinds of spin-flop domains, whereas the antiferromagnetic structure of the Mn sublattice remains intact as revealed by the quantitative analysis of the change in the neutron diffraction intensities. The present study provides a concrete basis to discuss the dominant role of the Eu sublattice on the enhanced two-dimensionality of the Dirac fermion transport in EuMnBi$_2$.
- arXiv:2003.03721 [pdf, other]
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Title: Ensemble averaged Madelung energies of finite volumes and surfacesAuthors: Peter KrügerComments: 15 pages, 3 figuresJournal-ref: Phys. Rev. B 101, 205423 (2020)Subjects: Statistical Mechanics (cond-mat.stat-mech); Materials Science (cond-mat.mtrl-sci)
Exact expressions for ensemble averaged Madelung energies of finite volumes are derived. The extrapolation to the thermodynamic limit converges unconditionally and can be used as a parameter-free real-space summation method of Madelung constants. In the large volume limit, the surface term of the ensemble averaged Madelung energy has a universal form, independent of the crystal structure. The scaling of the Madelung energy with system size provides a simple explanation for the structural phase transition observed in cesium halide clusters.
- arXiv:2003.03737 [pdf, other]
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Title: 3D motion of flexible ferromagnetic filaments under rotating magnetic fieldComments: Submitted to RSC Soft Matter Journal , uses rsc templateSubjects: Soft Condensed Matter (cond-mat.soft)
Ferromagnetic filaments in a rotating magnetic field are studied both numerically and experimentally. The filaments are made from micron-sized ferromagnetic particles linked with DNA strands. It is found that at low frequencies of the rotating field a filament rotates synchronously with the field and beyond a critical frequency it undergoes a transition to a three dimensional regime. In this regime the tips of the filament rotate synchronously with the field on circular trajectories in the plane parallel to the plane of the rotating field. The characteristics of this motion found numerically match the experimental data and allow us to obtain the physical properties of such filaments. We also discuss the differences in behaviour between magnetic rods and filaments and the applicability of filaments in mixing.
- arXiv:2003.03800 [pdf, ps, other]
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Title: One or two small points in thermodynamicsAuthors: Walter F. WreszinskiComments: 33 pages, important conceptual additions and corrections in section 5Subjects: Statistical Mechanics (cond-mat.stat-mech); Mathematical Physics (math-ph)
I present my recollections of what I used to find to be "one or two small points in thermodynamics", following Sommerfeld's famous quote, and review them on the light of present knowledge.
- arXiv:2003.03809 [pdf, other]
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Title: Half-space stationary Kardar-Parisi-Zhang equationComments: 50 pagesSubjects: Statistical Mechanics (cond-mat.stat-mech); Disordered Systems and Neural Networks (cond-mat.dis-nn); Mathematical Physics (math-ph); Probability (math.PR); Exactly Solvable and Integrable Systems (nlin.SI)
We study the solution of the Kardar-Parisi-Zhang (KPZ) equation for the stochastic growth of an interface of height $h(x,t)$ on the positive half line, equivalently the free energy of the continuum directed polymer in a half space with a wall at $x=0$. The boundary condition $\partial_x h(x,t)|_{x=0}=A$ corresponds to an attractive wall for $A<0$, and leads to the binding of the polymer to the wall below the critical value $A=-1/2$. Here we choose the initial condition $h(x,0)$ to be a Brownian motion in $x>0$ with drift $-(B+1/2)$. When $A+B \to -1$, the solution is stationary, i.e. $h(\cdot,t)$ remains at all times a Brownian motion with the same drift, up to a global height shift $h(0,t)$. We show that the distribution of this height shift is invariant under the exchange of parameters $A$ and $B$. For any $A,B > - 1/2$, we provide an exact formula characterizing the distribution of $h(0,t)$ at any time $t$, using two methods: the replica Bethe ansatz and a discretization called the log-gamma polymer, for which moment formulae were obtained. We analyze its large time asymptotics for various ranges of parameters $A,B$. In particular, when $(A,B) \to (-1/2,-1/2)$, the critical stationary case, the fluctuations of the interface are governed by a universal distribution that we express in terms of a simple Fredholm determinant, equivalently in terms of the Painlev\'e II transcendent, akin to the Baik-Rains distribution arising in stationary growth on the full-line. This provides an analog for the KPZ equation, of some of the results recently obtained by Betea-Ferrari-Occelli in the context of stationary half-space last-passage-percolation. From universality, we expect that limiting distributions found in both models can be shown to coincide.
- arXiv:2003.03833 [pdf]
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Title: The effect of material defects on resonant spin wave modes in a nanomagnetJournal-ref: Scientific Reports, 9, 16635 (2019)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Applied Physics (physics.app-ph)
We have theoretically studied how resonant spin wave modes in an elliptical nanomagnet are affected by fabrication defects, such as small local thickness variations. Our results indicate that defects of this nature, which can easily result from the fabrication process, or are sometimes deliberately introduced during the fabrication process, will significantly alter the frequencies, magnetic field dependence of the frequencies, and the power and phase profiles of the resonant spin wave modes. They can also spawn new resonant modes and quench existing ones. All this has important ramifications for multi-device circuits based on spin waves, such as phase locked oscillators for neuromorphic computing, where the device-to-device variability caused by defects can be inhibitory.
- arXiv:2003.03846 [pdf, ps, other]
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Title: Normal density and moment of inertia of a moving superfluidComments: 6 pagesSubjects: Quantum Gases (cond-mat.quant-gas)
In this work, the normal density $\rho_n$ and moment of inertia of a moving superfluid are investigated. We find that, even at zero temperature, there exists a finite normal density for the moving superfluid. When the velocity of superfluid reaches sound velocity, the normal density becomes total mass density $\rho$, which indicates that the system losses superfluidity. At the same time, the Landau's critical velocity also becomes zero. The existence of the non-zero normal density is attributed to the coupling between the motion of superflow and density fluctuation in transverse directions. With Josephson relation, the superfluid density $\rho_s$ is also calculated and the identity $\rho_s+\rho_n=\rho$ holds. Further more, we find that the finite normal density also results in a quantized moment of inertia in a moving superfluid trapped by a ring. The normal density and moment of inertia at zero temperature could be verified experimentally by measuring the angular momentum of a moving superfluid in a ring trap.
- arXiv:2003.03868 [pdf, other]
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Title: CP2K: An Electronic Structure and Molecular Dynamics Software Package -- Quickstep: Efficient and Accurate Electronic Structure CalculationsAuthors: Thomas D. Kühne, Marcella Iannuzzi, Mauro Del Ben, Vladimir V. Rybkin, Patrick Seewald, Frederick Stein, Teodoro Laino, Rustam Z. Khaliullin, Ole Schütt, Florian Schiffmann, Dorothea Golze, Jan Wilhelm, Sergey Chulkov, Mohammad Hossein Bani-Hashemian, Valéry Weber, Urban Borstnik, Mathieu Taillefumier, Alice Shoshana Jakobovits, Alfio Lazzaro, Hans Pabst, Tiziano Müller, Robert Schade, Manuel Guidon, Samuel Andermatt, Nico Holmberg, Gregory K. Schenter, Anna Hehn, Augustin Bussy, Fabian Belleflamme, Gloria Tabacchi, Andreas Glöß, Michael Lass, Iain Bethune, Christopher J. Mundy, Christian Plessl, Matt Watkins, Joost VandeVondele, Matthias Krack, Jürg HutterComments: 51 pages, 5 figuresSubjects: Chemical Physics (physics.chem-ph); Materials Science (cond-mat.mtrl-sci); Computational Physics (physics.comp-ph)
CP2K is an open source electronic structure and molecular dynamics software package to perform atomistic simulations of solid-state, liquid, molecular and biological systems. It is especially aimed at massively-parallel and linear-scaling electronic structure methods and state-of-the-art ab-initio molecular dynamics simulations. Excellent performance for electronic structure calculations is achieved using novel algorithms implemented for modern high-performance computing systems. This review revisits the main capabilities of CP2k to perform efficient and accurate electronic structure simulations. The emphasis is put on density functional theory and multiple post-Hartree-Fock methods using the Gaussian and plane wave approach and its augmented all-electron extension.
- arXiv:2003.03869 [pdf]
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Title: Optical Thermometry with Quantum Emitters in Hexagonal Boron NitrideAuthors: Yongliang Chen, Thinh Ngoc Tran, Ngoc My Hanh Duong, Chi Li, Milos Toth, Carlo Bradac, Igor Aharonovich, Alexander Solntsev, Toan Trong TranSubjects: Applied Physics (physics.app-ph); Materials Science (cond-mat.mtrl-sci); Optics (physics.optics)
Nanoscale optical thermometry is a promising non-contact route for measuring local temperature with both high sensitivity and spatial resolution. In this work, we present a deterministic optical thermometry technique based on quantum emitters in nanoscale hexagonal boron-nitride. We show that these nanothermometers exhibit better performance than that of homologous, all-optical nanothermometers both in sensitivity and range of working temperature. We demonstrate their effectiveness as nanothermometers by monitoring the local temperature at specific locations in a variety of custom-built micro-circuits. This work opens new avenues for nanoscale temperature measurements and heat flow studies in miniaturized, integrated devices.
- arXiv:2003.03871 [pdf, ps, other]
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Title: Accurate and efficient description of interacting carriers in quantum nanostructures by selected configuration interaction and perturbation theoryJournal-ref: Phys. Rev. B 101, 205308 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We present a method to calculate many-body states of interacting carriers in million atom quantum nanostructures based on atomistic tight-binding calculations and a combination of iterative selection of configurations and perturbation theory. This method enables investigations of large excitonic complexes and multi-electron systems with near full configuration interaction accuracy, even though only a small subspace of the full many-body Hilbert space is sampled, thus saving orders of magnitudes in computational resources. Important advantages of this method are that the convergence is controlled by a single parameter, the threshold, and that ground and excited states can be treated on an equal footing. We demonstrate the extreme efficiency of the method by numerical studies of complexes composed of up to 13 excitons, which requires filling of states up to the fourth electronic shell. We find that the method generally converges fast as a function of the threshold, profiting from a significant enhancement due to the perturbative corrections. The role of the choice of single-particle basis states is discussed. It is found that the algorithm converges faster in the Hartree-Fock basis only for highly charged systems, where Coulomb repulsion dominates. Finally, based on the observation that second order perturbative energy corrections only depend on off-diagonal elements of the many-body Hamiltonian, we present a way to accurately calculate many-body states that requires only a relatively small number of Coulomb matrix elements.
- arXiv:2003.03890 [pdf, ps, other]
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Title: Bending-induced director reorientation in a nematic liquid crystal elastomer bonded to a hyperelastic substrateComments: 15 pages, 4 figuresSubjects: Soft Condensed Matter (cond-mat.soft)
In this paper, the two-dimensional pure bending of a hyperelastic substrate coated by a nematic liquid crystal elastomer (abbreviated as NLCE) is studied within the framework of nonlinear elasticity. The governing system, arising from the deformational momentum balance, the orientational momentum balance and the mechanical constraint, is formulated, and the corresponding exact solution is derived for a given constitutive model. It is found that there exist two different bending solutions. In order to determine which the preferred one is, we compare the total potential energy for both solutions and find that the two energy curves may have an intersection point at a critical value of the bending angle $\alpha_c$ for some material parameters. In particular, the director $\bm n$ abruptly rotates $\dfrac{\pi}{2}$ from one solution to another at $\alpha_c$, which indicates a director reorientation (or jump). Furthermore, the effects of different material and geometric parameters on the bending deformation and the transition angle $\alpha_c$ can be revealed using the obtained bending solutions. Meanwhile, the exact solution can offer a benchmark problem for validating the accuracy of approximated plate models for liquid crystal elastomers.
- arXiv:2003.03895 [pdf, other]
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Title: Thickness-dependence of hydrogen-induced phase transition in MoTe$_{2}$Journal-ref: Phys. Rev. B 101, 144104 (2020)Subjects: Materials Science (cond-mat.mtrl-sci)
Two-dimensional transition metal dichalcogenides (TMDs) usually exist in two or more structural phases with different physical properties, and can be repeatedly switched between these phases via different stimuli, making them potentially useful for memory devices. An understanding of the physics of interfaces between the TMDs and conventional semiconductors, or other 2D-crystals forming heterogenous or homogeneous assemblies is central to their successful application in technologies. However, to date, most theoretical works have explored phase-change properties of isolated TMD monolayers in vacuum. Using \textit{ab-initio} calculations, we show how interfacial effects modify the thermodynamics and kinetics of the phase transition by studying hydrogen-induced transitions in monolayers and bilayers of MoTe$_{2}$. The phase-change properties of MoTe$_{2}$ show substantial thickness-dependence, with the timescale for a transition in the hydrogenated bilayer being about $10^7$-times longer than that in a monolayer at room temperature. Our study highlights the importance of taking effects of immediate environment into account when predicting properties of 2D crystals.
- arXiv:2003.03902 [pdf, ps, other]
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Title: The Schwartz-Soffer and more inequalities for random fieldsComments: 14 pagesSubjects: Mathematical Physics (math-ph); Disordered Systems and Neural Networks (cond-mat.dis-nn)
A new series of correlation inequalities for random field spin systems is proven rigorously. First one corresponds to the well-known Schwartz-Soffer inequality. These are expected to rule out incorrect results calculated in effective theories and numerical studies. The large $N$ expansion with the replica method for random field systems as an example is checked by these inequalities. It is shown that several critical exponents of multiple-point correlation functions at critical point satisfy obtained inequalities.
- arXiv:2003.03914 [pdf, other]
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Title: Revival dynamics in a traversable wormholeComments: 6+6 pages, 4+3 figures. Comments welcome. Note also an interesting parallel study by X.-L. Qi and P. Zhang that appeared in a parallel posting. v2: updated Fig. 1 and discussion, updated discussion of finite temperature effects, revised supplementary materialJournal-ref: Physical Review Letters 124, 221601 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el); High Energy Physics - Theory (hep-th); Quantum Physics (quant-ph)
Quantum effects can stabilize wormhole solutions in general relativity, allowing information and matter to be transported between two connected spacetimes. Here we study the revival dynamics of signals sent between two weakly coupled quantum chaotic systems, represented as identical Sachdev-Ye-Kitaev models, that realize holographically a traversable wormhole in anti-de Sitter spacetime AdS$_2$ for large number $N$ of particles. In this limit we find clear signatures of wormhole behavior: an excitation created in one system is quickly scrambled under its unitary dynamics, and is reassembled in the other system after a characteristic time consistent with holography predictions. This leads to revival oscillations that at low but finite temperature decay as a power-law in time. For small $N$ we also observe revivals and show that they arise from a different, non-gravitational mechanism.
- arXiv:2003.03916 [pdf, other]
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Title: The Coupled SYK model at Finite TemperatureComments: Note also an interesting parallel work on the revival dynamics in a traversable wormhole by S. Plugge, E. Lantagne-Hurtubise and M. Franz that appears in a parallel postingSubjects: High Energy Physics - Theory (hep-th); Strongly Correlated Electrons (cond-mat.str-el)
Sachdev-Ye-Kitaev (SYK) model, which describes $N$ randomly interacting Majorana fermions in 0+1 dimension, is found to be an solvable UV-complete toy model for holographic duality in nearly AdS$_2$ dilaton gravity. Ref. [1] proposed a modified model by coupling two identical SYK models, which at low-energy limit is dual to a global AdS$_2$ geometry. This geometry is an "eternal wormhole" because the two boundaries are causally connected. Increasing the temperature drives a Hawking-Page like transition from the eternal wormhole geometry to two disconnected black holes with coupled matter field. To gain more understanding of the coupled SYK model, in this work, we study the finite temperature spectral function of this system by numerical solving the Schwinger-Dyson equation in real-time. We find in the low-temperature phase the system is well described by weakly interacting fermions with renormalized single-particle gap, while in the high temperature phase the system is strongly interacting and the single-particle peaks merge. We also study the $q$ dependence of the spectral function.
- arXiv:2003.03928 [pdf, other]
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Title: Effective potential approach to hybrid synchronization transitionsComments: 12 pages, 13 figuresJournal-ref: Phys. Rev. E 101, 052313 (2020)Subjects: Statistical Mechanics (cond-mat.stat-mech)
The Kuramoto model exhibits different types of synchronization transitions depending on the type of natural frequency distribution. To obtain these results, the Kuramoto self-consistency equation (SCE) approach has been used successfully. However, this approach affords only limited understanding of more detailed properties such as the stability and finite size effect. Here, we extend the SCE approach by introducing an effective potential, that is, an integral version of the SCE. We examine the landscape of this effective potential for second-order, first-order, and hybrid synchronization transitions in the thermodynamic limit. In particular, for the hybrid transition, we find that the minimum of effective potential displays a plateau across the region in which the order parameter jumps. This result suggests that the effective free energy can be used to determine a type of synchronization transition. For finite systems, the effective potential contains local minima at which the system can be trapped. Using numerical simulations, we determine the stability of the system as a function of system size and simulation time.
- arXiv:2003.03936 [pdf, other]
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Title: Colossal quasiparticle radiation in the Lifshitz spin liquid phase of a two-dimensional quantum antiferromagnetComments: 10 pages, 4 figuresJournal-ref: Phys. Rev. B 101, 184408 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el)
Strong quantum fluctuations in magnetic systems can create disordered quantum spin liquid phases of matter which are not predicted by classical physics. The complexity of the exotic phenomena on display in spin liquids has led to a great deal of theoretical and experimental interest. However, understanding the fundamental nature of the excitations in these systems remains challenging. In this work, we consider the Lifshitz quantum critical point in a two-dimensional frustrated $XY$ antiferromagnet. At this point, quantum fluctuations destroy long range order, leading to the formation of an algebraic Lifshitz spin liquid. We demonstrate that the bosonic magnon excitations are long-lived and well-defined in the Lifshitz spin liquid phase, though paradoxically, the dynamic structure factor has a broad non-Lorentzian frequency distribution with no single-particle weight. We resolve this apparent contradiction by showing that the Lifshitz spin liquid suffers from an infrared catastrophe: An external physical probe always excites an infinite number of arbitrarily low energy quasiparticles, which leads to significant radiative broadening of the spectrum.
- arXiv:2003.03937 [pdf]
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Title: Chemical instability of free-standing boron monolayers and properties of oxidized borophene sheetsComments: 14 pages, 5 figures, accepted in Physica E journalSubjects: Materials Science (cond-mat.mtrl-sci); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Chemical Physics (physics.chem-ph); Computational Physics (physics.comp-ph)
In this work we report results of step-by-step modeling of the oxidation of free-standing boron monolayers of different types. Results of the calculations demonstrate that the process of the oxidation is always exothermic and lead toward the formation of foam-like boron oxide films with incorporated non-oxidized small boron clusters. Some of these boron-oxide films demonstrate the presence of chemically stable magnetic centers. Evaluation of the physical properties of oxidized boprophene sheets (OBS) demonstrate it possible application in solar energy, as sensors and coating against leakage of hydrogen.
- arXiv:2003.03939 [pdf]
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Title: Uncommon clustering in dilute Ti-Fe alloysComments: 11 pages 5 figures accepted in J. Phys.: MaterialsSubjects: Materials Science (cond-mat.mtrl-sci); Computational Physics (physics.comp-ph)
We present the results of ab initio modeling of structure of dilute Ti-Fe, a typical representative of quenched Ti-based transition-metal alloys. We have demonstrated that beyond the solubility limit this alloy cannot be described in common terms of substitutional and interstitial alloys. Instead, very stable local clusters are formed in both low-temperature hcp and high-temperature bcc phases of alloys, with almost identical local structures. This gives an example of geometrically frustrated state and explains unusual concentration behavior of M\"ossbauer spectra discovered long ago for this system.
- arXiv:2003.03958 [pdf, other]
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Title: Localization in one-dimensional relativistic quantum mechanicsComments: 14 pages, 11 figuresJournal-ref: Eur. Phys. J. B (2020) 93: 20Subjects: Disordered Systems and Neural Networks (cond-mat.dis-nn)
We present the relativistic analogue of Anderson localization in one dimension. We use Dirac equation to calculate the transmission probability for a spin-$\frac{1}{2}$ particle incident upon a rectangular barrier. Using the transfer matrix formalism, we numerically compute the transmission probability for the case of a large number of identical barriers spread randomly in one dimension. The particular case when the incident particle has three component momentum and shows spin-flip phenomena is also considered. Our calculations suggest that the incident relativistic particle shows localization behaviour similar to that of Anderson localization. A number of results which are generalizations of the non-relativistic case are also obtained.
- arXiv:2003.03974 [pdf, other]
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Title: Transiently changing shape of the photon number distribution in a quantum-dot--cavity system driven by chirped laser pulsesComments: 12 pages, 5 figuresJournal-ref: Phys. Rev. B 101, 205304 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Quantum Physics (quant-ph)
We have simulated the time evolution of the photon number distribution in a semiconductor quantum dot-microcavity system driven by chirped laser pulses and compare with unchirped results. When phonon interactions with the dot are disregarded - thus corresponding to the limit of atomic cavity systems - chirped pulses generate photon number distributions that change their shape drastically in the course of time. Phonons have a strong and qualitative impact on the photon statistics. The asymmetry between phonon absorption and emission destroys the symmetry of the photon distributions obtained for positive and negative chirps. While for negative chirps transient distributions resembling thermal ones are observed, for positive chirps the photon number distribution still resembles its phonon-free counterpart but with overall smoother shapes. In sharp contrast, using unchirped pulses of the same pulse area and duration wave-packets are found that move up and down the Jaynes-Cummings ladder with a bell-shape that changes little in time. For shorter pulses and lower driving strength Rabi-like oscillations occur between low photon number states. For all considered excitation conditions transitions between sub- and super-Poissonian statistics are found at certain times. For resonant driving with low intensity the Mandel parameter oscillates and is mostly negative, which indicates a non-classical state in the cavity field. Finally, we show that it is possible that the Mandel parameter dynamically approaches zero and still the photon distribution exhibits two maxima and thus is far from being a Poissonian.
- arXiv:2003.03978 [pdf]
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Title: Electrical and structural properties of pure and dysprosium doped $Na_{0.5}Bi_{0.5}TiO_{3}$ system: DFT and Monte Carlo simulationAuthors: Manal Benyoussef, Halima Zaari, Jamal Belhadi, Abdelilah Lahmar, Youssef El Amraoui, Hamid Ez-Zahraouy, Mimoun El MarssiSubjects: Materials Science (cond-mat.mtrl-sci)
The chemical ordering, electrical, optical, and magnetic properties of $Na_{0.5}Bi_{0.5}TiO_{3}$ (NBT) and 25$\%$ dysprosium doped NBT (DyNBT) were investigated in the framework of first-principles calculations using the full potential linearized augmented plane wave (FP-LAPW) method based on spin-polarized density functional theory implemented in the WIEN2k code. We demonstrated that NBT structure is stable in the 001 A-site configuration, while DyNBT presents an A-site disorder perceived by the minimal energy difference between the different A-site configurations. A significant magnetic moment of $5{\mu}B$ emerges in DyNBT system, while NBT is known to be non-magnetic. Dysprosium in NBT matrix seems to form an ionic bonding with oxygen atoms whereas Bi-O forms covalent bonding which is responsible for the decrease of the polarization value from 42.3 ${\mu}C/cm^{2}$ for NBT to 22.08 ${\mu}C/cm^{2}$ for the doped compound. In the second part, the transition temperature and the hysteresis loops of $Na_{0.5}(Bi_{1-x}Dy_{x})_{0.5}TiO_{3}$ system x = 0 - $25\%$ were investigated using the Monte Carlo simulation. We observed a decrease in the transition temperature as a function of dysprosium introduction. We pointed out from the hysteresis loops, an apparent decrease of the coercive field together with the remanent polarization as a function of doping and also as a function of temperature. Our proposed model was seen to approach the values of experimental studies.
- arXiv:2003.03980 [pdf, other]
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Title: Measuring out-of-time-ordered correlation functions without reversing time evolutionAuthors: Philip Daniel Blocher, Serwan Asaad, Vincent Mourik, Mark A. I. Johnson, Andrea Morello, Klaus MølmerComments: 5 pages, 3 figures. See the arXiv ancillary files for supplementary materialsSubjects: Quantum Physics (quant-ph); Statistical Mechanics (cond-mat.stat-mech)
Out-of-time-ordered correlation functions (OTOCs) play a crucial role in the study of thermalization, entanglement, and quantum chaos, as they quantify the scrambling of quantum information due to complex interactions. As a consequence of their out-of-time-ordered nature, OTOCs are difficult to measure experimentally. In this Letter we propose an OTOC measurement protocol that does not rely on the reversal of time evolution and is easy to implement in a range of experimental settings. We demonstrate application of our protocol by the characterization of quantum chaos in a periodically driven spin.
- arXiv:2003.03984 [pdf, other]
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Title: Quasistatic transfer protocols for atomtronic superfluid circuitsComments: 14 pages, 8 pagesSubjects: Statistical Mechanics (cond-mat.stat-mech); Quantum Gases (cond-mat.quant-gas)
Quasi-static protocols for systems that feature a mixed phase-space with both chaos and quasi-regular regions are beyond the standard paradigm of adiabatic processes. We focus on a many-body system of atoms that are described by the Bose-Hubbard Hamiltonian, specifically a circuit that consists of bosonic sites. We consider a sweep process: slow variation of the rotation frequency of the device (time dependent Sagnac phase). The parametric variation of phase-space topology implies that the quasi-static limit is irreversible. Detailed analysis is essential in order to determine the outcome of such transfer protocol, and its efficiency.
- arXiv:2003.03992 [pdf]
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Title: Reply to "Comment on 'Apical charge flux-modulated in-plane transport properties of cuprate superconductors'"Journal-ref: Phys. Rev. Lett. 124, 109702 (2020)Subjects: Superconductivity (cond-mat.supr-con)
This Reply to preceding Comment of arXiv:1909.09867 shows why the statements in the Comment are misleading. We point out that our physical picture and theirs are fundamentally different, therefore the claim of using their correlation to include ours shows a very limited physical relevance, which instead may impede the precise understanding of either of the two pictures.
- arXiv:2003.03996 [pdf, ps, other]
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Title: Microscopic Eilenberger theory of Fulde-Ferrell-Larkin-Ovchinnikov states in the presence of vorticesComments: 33 pages, 7 figuresSubjects: Superconductivity (cond-mat.supr-con)
We theoretically investigate the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state by using the microscopic quasi-classical Eilenberger equation. The Pauli paramagnetic effects and the orbital depairing effects due to vortices are treated in an equal footing for three dimensional spherical Fermi surface model and $s$-wave pairing. The field evolution of the LO state is studied in detail, such as the $H$-$T$ phase diagram, spatial structures of the order parameter, the paramagnetic moment, and the internal filed. Field-dependences of various thermodynamic quantities: the paramagnetic moment, entropy, and the zero-energy density of states are calculated. Those quantities are shown to start quickly growing upon entering the LO state. We also evaluate the wave length of the LO modulation, the flux line lattice form factors for small angle neutron scattering, and the NMR spectra to facilitate the identification of the LO state. Two cases of strong and intermediate Pauli paramagnetic effect are studied comparatively. The possibility of the LO phase in Sr$_2$RuO$_4$, CeCoIn$_5$, CeCu$_2$Si$_2$, and the organic superconductors is critically examined and crucial experiments to identify it are proposed.
- arXiv:2003.04012 [pdf, other]
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Title: Chirality-induced bacterial rheotaxis in bulk shear flowsComments: 13 pages, 6 figuresSubjects: Soft Condensed Matter (cond-mat.soft); Biological Physics (physics.bio-ph); Fluid Dynamics (physics.flu-dyn)
Interaction of swimming bacteria with flows controls their ability to explore complex environments, crucial to many societal and environmental challenges and relevant for microfluidic applications as cell sorting. Combining experimental, numerical and theoretical analysis, we present a comprehensive study of the transport of motile bacteria in shear flows. Experimentally, we obtain with high accuracy and for a large range of flow rates, the spatially resolved velocity and orientation distributions. They are in excellent agreement with the simulations of a kinematic model accounting for stochastic and microhydrodynamic properties and in particular the flagella chirality. Theoretical analysis reveals the scaling laws behind the average rheotactic velocity at moderate shear rates using a chirality parameter and explains the reorientation dynamics leading to a saturation at large shear rates from the marginal stability of a fixed point. Our findings constitute a full understanding of the physical mechanisms and relevant parameters of bacteria bulk rheotaxis.
- arXiv:2003.04015 [pdf, other]
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Title: Superconducting mechanism for a new-type cuprate Ba$_2$CuO$_{3+δ}$ based on a multiorbital Lieb lattice modelAuthors: Kimihiro Yamazaki, Masayuki Ochi, Daisuke Ogura, Kazuhiko Kuroki, Hiroshi Eisaki, Shinichi Uchida, Hideo AokiComments: 19 pages, 20 figures, references updatedSubjects: Superconductivity (cond-mat.supr-con)
For a recently discovered new-type cuprate superconductor $\mathrm{Ba_{2}CuO_{3+\delta}}$, we propose a lattice structure which resembles the model considered by Lieb to represent the vastly oxygen-deficient material. We first investigate the stability of the Lieb-lattice structure, and then construct a multiorbital Hubbard model based on first-principles calculation. By applying the fluctuation-exchange approximation to the model and solving the linearized Eliashberg equation, we show that $s$-wave and $d$-wave pairings closely compete with each other, and, more interestingly, that the intra-orbital and inter-orbital pairings coexist. We further show that, if the energy of the $d_{3z^2-r^2}$ band is raised to make it "incipient" with the lower edge of the band close to the Fermi level within a realistic band filling regime, $s\pm$-wave superconductivity is strongly enhanced. We reveal an intriguing relation between the Lieb model and the two-orbital model for the usual K$_2$NiF$_4$ structure where a close competition between $s-$ and $d-$wave pairings is known to occur. The enhanced superconductivity in the present model is further shown to be related to an enhancement found previously in the bilayer Hubbard model with an incipient band.
- arXiv:2003.04023 [pdf, other]
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Title: Josephson radiation in a superconductor-quantum dot-superconductor junctionComments: 5+4 pages, 4 + 2 figuresSubjects: Superconductivity (cond-mat.supr-con); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We investigate the Josephson radiation emitted by a junction made of a quantum dot coupled to two conventional superconductors. Close to resonance, the particle-hole symmetric Andreev states that form in the junction are detached from the continuum above the superconducting gap in the leads, while a gap between them opens near the Fermi level. Under voltage bias, we formulate a stochastic model that accounts for non-adiabatic processes, which change the occupations of the Andreev states. This model allows calculating the current noise spectrum and determining the Fano factor. Analyzing the finite-frequency noise, we find that the model may exhibit either an integer or a fractional AC Josephson effect, depending on the bias voltage and the size of the gaps in the Andreev spectrum. Our results assess the limitations in using the fractional Josephson radiation as a probe of topology.
- arXiv:2003.04034 [pdf, other]
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Title: Ab initio description of the Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ electronic structureAuthors: J. Nokelainen, C. Lane, R. S. Markiewicz, B. Barbiellini, A. Pulkkinen, B. Singh, J. Sun, K. Pussi, A. BansilSubjects: Superconductivity (cond-mat.supr-con)
Bi-Sr-Ca-Cu-O superconductors are important materials for both fundamental research and applications. As in other cuprates, the superconducting phase in these Bi-compounds lies close to an antiferromagnetic phase. Density functional theory calculations based on the strongly-constrained-and-appropriately-normed (SCAN) exchange correlation functional in Bi$_2$Sr$_2$CuO$_6$ and Bi$_2$Sr$_2$CaCu$_2$O$_8$ reveal the persistence of magnetic moments on the copper ions for oxygen concentrations ranging from the pristine phase to the optimally hole-doped compound. We also find the existence of ferrimagnetic solutions in the heavily doped compounds, which are expected to suppress superconductivity.
- arXiv:2003.04042 [pdf]
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Title: A simple approach to model the yield strength of body centered cubic solid solution refractory high entropy alloysAuthors: Ali ShafieiSubjects: Materials Science (cond-mat.mtrl-sci)
A simple fitting approach is used for modeling the compressive yield strength of body centered cubic (bcc) solid solution high entropy alloys in Al-Hf-Nb-Mo-Ta-Ti-V-Zr system. It is proposed that the yield strength could be modeled by a polynomial where the experimental data can be used for finding the polynomial coefficients. The results show that the proposed polynomial could model the yield strength of solid solution alloys relatively well. The developed polynomial is used for predicting the strength of RHEAs in Hf-Mo-Nb-Ta-Ti-V-Zr system. It is observed that the yield strength of alloys within this system increases with the additions of Mo and Zr and decreases with the addition of Ti. Furthermore, the model predicts that the yield strength increases with increasing the value of parameters valence electron concentration (VEC) and atomic size difference (ASD). Although the developed polynomial does not consider the mechanisms involved in the strengthening of alloys, it can be considered as a straightforward method for assessing the strength of solid solution RHEAs.
- arXiv:2003.04043 [pdf, other]
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Title: Scaling behavior of crystalline membranes: an $ε$-expansion approachComments: 15 pages, 4 figuresJournal-ref: Nuclear Physics B 956 (2020) 115040Subjects: Statistical Mechanics (cond-mat.stat-mech)
We study the scaling behavior of two-dimensional (2D) crystalline membranes in the flat phase by a renormalization group (RG) method and an $\epsilon$-expansion. Generalization of the problem to non-integer dimensions, necessary to control the $\epsilon$-expansion, is achieved by dimensional continuation of a well-known effective theory describing out-of-plane fluctuations coupled to phonon-mediated interactions via a scalar composite field, equivalent for small deformations to the local Gaussian curvature. The effective theory, which will be referred to as Gaussian curvature interaction (GCI) model, is equivalent to theories of elastic $D$-dimensional manifolds fluctuating in a $(D + d_{c})$-dimensional embedding space in the physical case $D = 2$ for arbitrary $d_{c}$. For $D\neq 2$, instead, the GCI model is not equivalent to a direct dimensional continuation of elastic membrane theory and it defines an alternative generalization to generic internal dimension $D$. We calculate explicitly RG functions at two-loop order and determine the exponent $\eta$ characterizing the long-wavelength scaling of correlation functions to order $\epsilon^{2}$ in an $\epsilon=(4-D)$-expansion. The self-consistent screening approximation (SCSA) for the GCI model is shown to be exact to O($\epsilon^{2}$). For $d_{c} = 1$, the O($\epsilon^{2}$) correction is suppressed by a small numerical prefactor. As a result, despite the large value of $\epsilon = 2$, extrapolation of the first and second order results to $D = 2$ leads to very close numbers, $\eta = 0.8$ and $\eta \simeq 0.795$. The calculated exponent values are close to earlier reference results obtained by non-perturbative RG, the SCSA and numerical simulations. These indications suggest that a perturbative analysis of the GCI model could provide an useful framework for accurate quantitative predictions of the scaling exponent even at $D = 2$.
- arXiv:2003.04050 [pdf, other]
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Title: Two-electron selective coupling in an edge-state based conditional phase shifterComments: 10 pages, double column, 7 figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We investigate the effect of long-range Coulomb interaction on the two-electron scattering in the integer quantum Hall regime at bulk filling factor 2. A parallel version of the Split-Step Fourier method evolves the exact two-particle wave function in a 2D potential background reproducing the effect of depleting gates in a realistic heterostructure, with the charge carrier represented by a localized wavepacket of edge states. We compare the spatial shift induced by Coulomb repulsion in the final two-electron wave function for two indistinguishable electrons initialized in different configurations according to their Landau index, and analyze their bunching probability and the effect of screening. We finally prove the feasibility of the present operating regime as a two-qubit conditional phase shifter to generate entanglement from product states.
- arXiv:2003.04053 [pdf, other]
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Title: All-electrically tunable networks of Majorana bound statesComments: 7 pages, 4 figuresSubjects: Superconductivity (cond-mat.supr-con); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci)
Second-order topological superconductors (SOTSs) host localized Majorana fermions and provide a new platform for topological quantum computation. We propose a remarkable and feasible way to realize networks based on SOTSs which allow to nucleate and braid Majorana bound states (MBSs) in an all-electrical manner without fine-tuning. The proposed setups are scalable in a straightforward way and can accommodate any even number of MBSs. Moreover, the MBSs in the networks allow defining qubits whose states can be initialized and read out by measuring Josephson currents flowing between SOTS islands. Our proposal can be implemented in monolayers of $\text{FeTe}{}_{1-x}\text{Se}_{x}$ and inverted Hg(Cd)Te quantum wells in proximity to conventional superconductors.
- arXiv:2003.04055 [pdf, ps, other]
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Title: Spin-Triplet Superconductivity in UTe2 and Ferromagnetic SuperconductorsAuthors: Dai Aoki, Ai Nakamura, Fuminori Honda, DeXin Li, Yoshiya Homma, Yusei Shimizu, Yoshiki J. Sato, Georg Knebel, Jean-Pascal Brison, Alexandre Pourret, Daniel Braithwaite, Gerard Lapertot, Qun Niu, Michal Valiska, Hisatomo Harima, Jacques FlouquetComments: 6 pages, 3 figures, accepted for publication in JPSJ Conference ProceedingsSubjects: Strongly Correlated Electrons (cond-mat.str-el); Superconductivity (cond-mat.supr-con)
The spin-triplet state is most likely realized in uranium ferromagnetic superconductors, UGe2, URhGe, UCoGe. The microscopic coexistence of ferromagnetism and superconductivity means that the Cooper pair should be realized under the strong internal field due the ferromagnetism, leading to the spin-triplet state with equal spin pairing. The field-reinforced superconductivity, which is observed in all three materials when the ferromagnetic fluctuations are enhanced, is one of the strong evidences for the spin-triplet superconductivity. We present here the results of a newly discovered spin-triplet superconductor, UTe2, and compare those with the results of ferromagnetic superconductors. Although no magnetic order is found in UTe2, there are similarities between UTe2 and ferromagnetic superconductors. For example, the huge upper critical field exceeding the Pauli limit and the field-reentrant superconductivity for H || b-axis are observed in UTe2, URhGe and UCoGe. We also show the specific heat results on UTe2 in different quality samples, focusing on the residual density of states in the superconducting phase.
- arXiv:2003.04058 [pdf, ps, other]
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Title: Forces between Silica Particles in Isopropanol Solutions of 1:1 ElectrolytesSubjects: Soft Condensed Matter (cond-mat.soft)
Interactions between silica surfaces across isopropanol solutions are measured with colloidal probe technique based on atomic force microscope. In particular, the influence of 1:1 electrolytes on the interactions between silica particles is investigated. A plethora of different forces are found in these systems. Namely, van der Waals, double-layer, attractive non-DLVO, repulsive solvation, and damped oscillatory interactions are observed. The measured decay length of the double-layer repulsion is substantially larger than Debye lengths calculated from nominal salt concentrations. These deviations are caused by pronounced ion pairing in alcohol solutions. At separation below 10 nm, additional attractive and repulsive non-DLVO forces are observed. The former are possibly caused by charge heterogeneities induced by strong ion adsorption, whereas the latter originate from structuring of isopropanol molecules close to the surface. Finally, at increased concentrations the transition from monotonic to damped oscillatory interactions is uncovered.
- arXiv:2003.04059 [pdf, other]
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Title: Ultrafast Light-Induced Lifshitz TransitionAuthors: Samuel Beaulieu, Shuo Dong, Nicolas Tancogne-Dejean, Maciej Dendzik, Tommaso Pincelli, Julian Maklar, R. Patrick Xian, Michael A. Sentef, Martin Wolf, Angel Rubio, Laurenz Rettig, Ralph ErnstorferSubjects: Strongly Correlated Electrons (cond-mat.str-el); Materials Science (cond-mat.mtrl-sci)
Fermi surface is at the heart of our understanding of metals and strongly correlated many-body systems. An abrupt change in the Fermi surface topology, also called Lifshitz transition, can lead to the emergence of fascinating phenomena like colossal magnetoresistance and superconductivity. While Lifshitz transitions have been demonstrated for a broad range of materials and using different types of static external perturbations such as strain, doping, pressure and temperature, a non-equilibrium route toward ultrafast and transient modification of the Fermi surface topology has not been experimentally demonstrated. Combining time-resolved multidimensional photoemission spectroscopy with state-of-the-art TDDFT+U simulations, we introduce a scheme for driving an ultrafast Lifshitz transition in the correlated Weyl semimetal T$\mathrm{_{d}}$-MoTe$_{2}$. We demonstrate that this non-equilibrium topological electronic transition finds its microscopic origin in the dynamical modification of the effective electronic correlations. These results shed light on a novel ultrafast and all-optical scheme for controlling the Fermi surface topology in correlated quantum materials.
- arXiv:2003.04068 [pdf, other]
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Title: A Hilbert Transform method for measuring linear and nonlinear phase shifts imparted by metasurfacesComments: 13 pages, 4 figure, underlying data to be shared upon publicationSubjects: Optics (physics.optics); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Instrumentation and Detectors (physics.ins-det)
Nonlinear metasurfaces that dynamically manipulate the phase of a passing light beam are of interest for a wide range of applications. The controlled operation of such devices requires accurate measurements of the optical transmission phase in both the linear and nonlinear regime, an experimentally challenging task. In this paper we show that this phase information can be extracted directly from simple transmission measurements, using a Hilbert transform approach, removing the need for complicated, interferometric experimental set-ups, and enabling direct measurements of the phase in conditions not suitable for other traditional approaches, such Z-scan measurements.
- arXiv:2003.04082 [pdf, other]
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Title: Weyl semimetals and spin$^c$ cobordismAuthors: Ümit ErtemComments: 12 pages, minor modificationsSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Strongly Correlated Electrons (cond-mat.str-el); High Energy Physics - Theory (hep-th); Mathematical Physics (math-ph)
Classification of topological insulators and superconductors is manifested in terms of spin cobordism groups for lower dimensions. It is discussed that the periodic table of topological insulators is a result of the possible choices of spin structures on Brillouin zones of relevant topological materials. This framework is extended to the case of Weyl semimetals. It is shown that the classification of Weyl semimetals can be managed in terms of spin$^c$ cobordism groups via the extension of spin structures to spin$^c$ structures. Topological invariants of Weyl semimetals are connected to the topological invariants of spin$^c$ cobordism groups and Fermi arcs of Weyl semimetals are interpreted in terms of the choices of spin$^c$ structures.
- arXiv:2003.04083 [pdf]
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Title: Mathematical Model of a Direct Methanol Fuel CellComments: 30 pages, 7 figuresJournal-ref: Journal of Fuel Cell Science and Technology, 1 (1), 43-48, 2004Subjects: Chemical Physics (physics.chem-ph); Materials Science (cond-mat.mtrl-sci); Applied Physics (physics.app-ph)
A one dimensional (1-D), isothermal model for a direct methanol fuel cell (DMFC) is presented. This model accounts for the kinetics of the multi-step methanol oxidation reaction at the anode. Diffusion and crossover of methanol are modeled and the mixed potential of the oxygen cathode due to methanol crossover is included. Kinetic and diffusional parameters are estimated by comparing the model to data from a 25 cm2 DMFC. This semi-analytical model can be solved rapidly so that it is suitable for inclusion in real-time system level DMFC simulations.
- arXiv:2003.04085 [pdf]
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Title: The Influence of Elastic Strain on Catalytic Activity Towards the Hydrogen Evolution ReactionAuthors: Kai Yan, Tuhina Adit Maark, Alireza Khorshidi, Vijay A. Sethuraman, Andrew Peterson, Pradeep R. GuduruComments: 24 pages, 9 figuresJournal-ref: Angewandte Chemie International Edition, 55, 6175-6181, 2016Subjects: Applied Physics (physics.app-ph); Materials Science (cond-mat.mtrl-sci)
Understanding the role of elastic strain in modifying catalytic reaction rates is crucial for catalyst design, but experimentally, this effect is often coupled with a ligand effect. To isolate the strain effect, we have investigated the influence of externally applied elastic strain on the catalytic activity of metal films towards the hydrogen evolution reaction (HER). We show that elastic strain tunes the catalytic activity in a controlled and predictable way. Both theory and experiment show strain controls reactivity in a controlled manner consistent with the qualitative predictions of the HER volcano plot and the d-band theory: Ni and Pt activity were accelerated by compression, while Cu activity was accelerated by tension. By isolating the elastic strain effect from the ligand effect, this study provides a greater insight into the role of elastic strain in controlling electrocatalytic activity.
- arXiv:2003.04098 [pdf, ps, other]
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Title: Origins of magnetic field-dependent open-circuit voltage hysteresis driven by transverse charge current in ferromagnet/normal metal structuresAuthors: Christos TengerisSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Recent experimental work on Au thin films demonstrated signs of charge current-induced spin polarization through open circuit voltage measurements. In this study, we are investigating the underlying mechanism(s) that induces this measured signal in the Au devices. We determine the theoretically expected spin polarization from both Rashba-Edelstein effect and bulk spin Hall effect. The discrepancy in the scaling of the measured signal as a function of the thickness of the Au thin film in the two cases is our key to differentiate between the two effects when compared to experimental data. Experiments show reversal of spin polarization at a critical thickness which reveals the presence of multiple spin polarization mechanisms. Characteristics of both RashbaEdelstein and spin Hall effects are observed in different thickness regimes. In addition, we study the magnetoresistance of the same Au samples, which reveal the presence of weak anti-localization (WAL) at low temperatures for the low-thickness samples. More interestingly, it is revealed that the open circuit voltage difference and magnetoresistance due to WAL have very similar scaling with film thickness and temperature, suggesting the crucial importance of spin-orbit interaction in understanding the phenomenon.
- arXiv:2003.04100 [pdf, ps, other]
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Title: Tunable Casimir equilibria with phase change materials: from quantum trapping to its releaseComments: 9 pages, 7 figuresJournal-ref: Phys. Rev. B 101, 104107 (2020)Subjects: Applied Physics (physics.app-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Optics (physics.optics)
A stable suspension of nanoscale particles due to the Casimir force is of great interest for many applications such as sensing, non-contract nano-machines. However, the suspension properties are difficult to change once the devices are fabricated. Vanadium dioxide (VO$_2$) is a phase change material, which undergoes a transition from a low-temperature insulating phase to a high-temperature metallic phase around a temperature of 340 K. In this work, we study Casimir forces between a nanoplate (gold or Teflon) and a layered structure containing a VO$_2$ film. It is found that stable Casimir suspensions of nanoplates can be realized in a liquid environment, and the equilibrium distances are determined, not only by the layer thicknesses but also by the matter phases of VO$_2$. Under proper designs, a switch from quantum trapping of the gold nanoplate ("on" state) to its release ("off" state) as a result of the metal-to-insulator transition of VO$_2$, is revealed. On the other hand, the quantum trapping and release of a Teflon nanoplate is found under the insulator-to-metal transition of VO$_2 $. Our findings offer the possibility of designing switchable devices for applications in micro-and nano-electromechanical systems.
- arXiv:2003.04119 [pdf]
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Title: Anisotropic circular photogalvanic effect in colloidal tin sulfide nanosheetsComments: 16 pages, 3 figuresJournal-ref: Nanoscale 12 (2020) 6256Subjects: Materials Science (cond-mat.mtrl-sci)
Tin sulfide promises very interesting properties such as a high optical absorption coefficient and a small band gap, while being less toxic compared to other metal chalcogenides. However, the limitations in growing atomically thin structures of tin sulfide hinder the experimental realization of these properties. Due to the flexibility of the colloidal synthesis, it is possible to synthesize very thin and at the same time large nanosheets. Electrical transport measurements show that these nanosheets can function as field-effect transistors with high on/off ratio and p-type behavior. The temperature dependency of the charge transport reveals that defects in the crystal are responsible for the formation of holes as majority carriers. During illumination with circularly polarized light, these crystals generate a helicity dependent photocurrent at zero-volt bias, since their symmetry is broken by asymmetric interfaces (substrate and vacuum). Further, the observed circular photogalvanic effect shows a pronounced in-plane anisotropy, with a higher photocurrent along the armchair direction, originating from the higher absorption coefficient in this direction. Our new insights show the potential of tin sulfide for new functionalities in electronics and optoelectronics, for instance as polarization sensors.
- arXiv:2003.04120 [pdf, other]
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Title: Exciton-polariton interference controlled by electric fieldComments: 30 pages, 6 figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Linear in the wave-vector terms of an electron Hamiltonian play an important role in topological insulators and spintronic devices. Here we demonstrate how an external electric field controls the magnitude of a linear-in-K term in the exciton Hamiltonian in wide GaAs quantum wells. The dependence of this term on the applied field in a high quality sample was studied by means of the differential reflection spectroscopy. An excellent agreement between the experimental data and the results of calculations using semi-classical non-local dielectric response model confirms the validity of the method and paves the way for the realisation of excitonic Datta-and-Das transistors. In full analogy with the spin-orbit transistor proposed by Datta and Das [Appl. Phys. Lett. {\bf 56}, 665 (1990)], the switch between positive and negative interference of exciton polaritons propagating forward and backward in a GaAs film is achieved by application of an electric field with non-zero component in the plane of the quantum well layer.
- arXiv:2003.04154 [pdf, other]
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Title: Effective triangular ladders with staggered flux from spin-orbit coupling in 1D optical latticesComments: 12 pages, 6 figures. Accepted for publication in The European Physical Journal D, Topical issue: Topological Ultracold Atoms and Photonic SystemsSubjects: Quantum Gases (cond-mat.quant-gas); Strongly Correlated Electrons (cond-mat.str-el); Quantum Physics (quant-ph)
Light-induced spin-orbit coupling is a flexible tool to study quantum magnetism with ultracold atoms. In this work we show that spin-orbit coupled Bose gases in a one-dimensional optical lattice can be mapped into a two-leg triangular ladder with staggered flux following a lowest-band truncation of the Hamiltonian. The effective flux and the ratio of the tunneling strengths can be independently adjusted to a wide range of values. We identify a certain regime of parameters where a hard-core boson approximation holds and the system realizes a frustrated triangular spin ladder with tunable flux. We study the properties of the effective spin Hamiltonian using the density-matrix renormalization-group method and determine the phase diagram at half-filling. It displays two phases: a uniform superfluid and a bond-ordered insulator. The latter can be stabilized only for low Raman detuning. Finally, we provide experimentally feasible trajectories across the parameter space of the SOC system that cross the predicted phase transition.
- arXiv:2003.04162 [pdf, ps, other]
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Title: Phenomenological theory in reentrant uranium-based superconductorsComments: 4 pages, 3 figure, +appendixSubjects: Superconductivity (cond-mat.supr-con); Materials Science (cond-mat.mtrl-sci); Strongly Correlated Electrons (cond-mat.str-el)
We develop a phenomenological theory for the family of uranium-based heavy fermion superconductors ($URhGe$, $UCoGe$, and $UTe_2$ ). The theory unifies the understanding of both superconductivity(SC) with a weak magnetic field and reentrant superconductivity(RSC) that appears at the first-order transition line with a high magnetic field. It is shown that the magnetizations along the easy and hard axis have opposite effects on superconductivity. The RSC is induced by the fluctuation parallel to the direction of the magnetic field. The theory makes specific predictions about the variation of triplet superconductivity order parameters $\vec{d}$ with applied external magnetic fields and the existence of a metastable state for the appearance of the RSC.
- arXiv:2003.04166 [pdf, other]
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Title: Learning entropy production via neural networksComments: 10 pages, 8 figuresSubjects: Statistical Mechanics (cond-mat.stat-mech); Machine Learning (cs.LG); Machine Learning (stat.ML)
This Letter presents a neural estimator for entropy production, or NEEP, that estimates entropy production (EP) from trajectories without any prior knowledge of the system. For steady state, we rigorously prove that the estimator, which can be built up from different choices of deep neural networks, provides stochastic EP by optimizing the objective function proposed here. We verify the NEEP with the stochastic processes of the bead-spring and discrete flashing ratchet models, and also demonstrate that our method is applicable to high-dimensional data and non-Markovian systems.
- arXiv:2003.04171 [pdf, other]
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Title: Robust decompositions of quantum statesAuthors: Jonathan E. MoussaComments: March Meeting version of the paperSubjects: Quantum Physics (quant-ph); Strongly Correlated Electrons (cond-mat.str-el); Computational Physics (physics.comp-ph)
Classical-quantum computational complexity separations are an important motivation for the long-term development of digital quantum computers, but classical-quantum complexity equivalences are just as important in our present era of noisy intermediate-scale quantum devices for framing near-term progress towards quantum supremacy. We establish one such equivalence using a noisy quantum circuit model that can be simulated efficiently on classical computers. With respect to its noise model, quantum states have a robust decomposition into a sequence of operations that each extend the state by one qubit without spreading errors between qubits. This enables universal quantum sampling of states with an efficient representation in this robust form and observables with low quantum weight that can be sampled from general measurements on a few qubits and computational basis measurements on the remaining qubits. These robust decompositions are not unique, and we construct two distinct variants, both of which are compatible with machine-learning methodology. They both enable efficiently computable lower bounds on von Neumann entropy and thus can be used as finite-temperature variational quantum Monte Carlo methods.
- arXiv:2003.04181 [pdf, other]
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Title: Interplay between chemical order and magnetic properties in L1$_0$ FeNi (tetrataenite): A First-Principles StudySubjects: Materials Science (cond-mat.mtrl-sci)
We use first-principles-based calculations to investigate the interplay between chemical order and the magnetic properties of $L1_0$ FeNi. In particular, we investigate how deviations from perfect chemical order affect the energy difference between the paramagnetic and ferromagnetic states as well as the important magneto-crystalline anisotropy energy. Our calculations demonstrate a strong effect of the magnetic order on the chemical order-disorder transition temperature, and conversely, a strong enhancement of the magnetic transition temperature by the chemical order. Most interestingly, our results indicate that the magnetic anisotropy does not decrease significantly as long as the deviations from perfect order are not too large. Moreover, we find that in certain cases a slight disorder can result in a higher anisotropy than for the fully ordered structure. We further analyze the correlation between the magneto-crystalline anisotropy and the orbital magnetic moment anisotropy, which allows to study the effect of the local chemical environment on both quantities, potentially enabling further optimization of the magneto-crystalline anisotropy with respect to chemical order and stoichiometric composition.
- arXiv:2003.04183 [pdf, other]
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Title: A Mountaineering Strategy to Excited States: Highly-Accurate Energies and Benchmarks for Exotic Molecules and RadicalsComments: 19 pages, 2 figures, Supplementary information availableSubjects: Chemical Physics (physics.chem-ph); Materials Science (cond-mat.mtrl-sci); Strongly Correlated Electrons (cond-mat.str-el); Computational Physics (physics.comp-ph)
Aiming at completing the sets of FCI-quality transition energies that we recently developed (\textit{J.~Chem.~Theory Comput.} \textbf{14} (2018) 4360--4379, \textit{ibid.}~\textbf{15} (2019) 1939--1956, and \textit{ibid.}~\textbf{16} (2020) 1711--1741), we provide, in the present contribution, ultra-accurate vertical excitation energies for a series of "exotic" closed-shell molecules containing F, Cl, P, and Si atoms and small radicals, such as CON and its variants, that were not considered to date in such investigations. This represents a total of 81 high-quality transitions obtained with a series of diffuse-containing basis sets of various sizes. For the exotic compounds, these transitions are used to perform benchmarks with a vast array of lower-level models, $\textit{i.e.}$ CIS(D), EOM-MP2, (SOS/SCS)-CC2, STEOM-CCSD, CCSD, CCSDR(3), CCSDT-3, (SOS-)ADC(2), and ADC(3). Additional comparisons are made with literature data. For the open-shell compounds, we have compared the performances of both the unrestricted and restricted open-shell CCSD and CC3 formalisms.
- arXiv:2003.04190 [pdf, other]
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Title: Equation of motion truncation scheme based on partial orthogonalizationComments: 12 pages, 17 figuresSubjects: Strongly Correlated Electrons (cond-mat.str-el)
We introduce a general scheme to consistently truncate equations of motion for Green's functions. Our scheme is guaranteed to generate physical Green's functions with real excitation energies and positive spectral weights. There are free parameters in our scheme akin to mean field parameters that may be determined to get as good an approximation to the physics as possible. As a test case we apply our scheme to a two-pole approximation for the 2D Hubbard model. At half-filling we find an insulating solution with several interesting properties: it has low expectation value of the energy and it gives upper and lower Hubbard bands with the full non-interacting bandwidth in the large U limit. Away from half-filling, in particular in the intermediate interaction regime, our scheme allows for several different phases with different number of Fermi surfaces and topologies.
- arXiv:2003.04200 [pdf, other]
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Title: The impact of magnetic field on the conformations of supracolloidal polymer-like structures with super-paramagnetic monomersJournal-ref: Journal of Molecular Liquids (2020): 112761Subjects: Soft Condensed Matter (cond-mat.soft); Computational Physics (physics.comp-ph)
We investigate the properties of magnetic supracolliodal polymers -- magnetic filaments (MFs) -- with super-paramagnetic monomers, with and without Van der Waals (VdW) attraction between them. We employ molecular dynamics (MD) simulations to elucidate the impact of crosslinking mechanism on the structural and magnetic response of MFs to an applied external homogeneous magnetic field. We consider two models: plain crosslinking, which results in a flexible backbone; and constrained crosslinking, which provides significant stiffens against bending. We find that for plain crosslinking, even a slight increase of the central attraction leads to collapsed MF conformations. Structures that initially exhibit spherical symmetry evolve into cylindrically symmetric ones, with growing magnetic field strength. Plain crosslinking also allows for conformational bistability. MFs with constrained crosslinking tend to, instead, unravel in field. In both crosslinking scenarios, central attraction is able to hinder low-field magnetic response of MFs, albeit the bistability of plainly crosslinked MFs manifests itself also in the high-field region.
- arXiv:2003.04206 [pdf, other]
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Title: Dispersal-induced instability in complex ecosystemsComments: 30 pages, 6+1 figuresSubjects: Populations and Evolution (q-bio.PE); Disordered Systems and Neural Networks (cond-mat.dis-nn)
In his seminal work in the 1970s Robert May suggested that there was an upper limit to the number of species that could be sustained in stable equilibrium by an ecosystem. This deduction was at odds with both intuition and the observed complexity of many natural ecosystems. The so-called stability-diversity debate ensued, and the discussion about the factors making an ecosystem stable or unstable continues to this day. We show in this work that dispersal can be a destabilising influence. To do this, we combine ideas from Alan Turing's work on pattern formation with May's random-matrix approach. We demonstrate how a stable equilibrium in a complex ecosystem with two trophic levels can become unstable with the introduction of dispersal in space. Conversely, we show that Turing instabilities can occur more easily in complex ecosystems with many species than in the case of only a few species. Our work shows that adding more details to the model of May gives rise to more ways in which an equilibrium can become unstable. Making May's simple model more realistic is therefore unlikely to remove the upper bound on complexity.
- arXiv:2003.04211 [pdf, other]
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Title: Gutzwiller Hybrid Quantum-Classical Computing Approach for Correlated MaterialsComments: 12 pages, 4 figuresSubjects: Strongly Correlated Electrons (cond-mat.str-el); Materials Science (cond-mat.mtrl-sci); Computational Physics (physics.comp-ph)
Inspired by the fast-pace evolution of noisy intermediate-scale quantum (NISQ) computing technology, novel resource-efficient hybrid quantum-classical approaches are under active development to address grand scientific challenges faced by classical computations. Proof-of-principle applications of NISQ technology in quantum chemistry have been reported in solving ground state properties of small molecules. While several approaches have also been proposed to address the long-standing strongly correlated materials problem, a complete calculation of periodic correlated electron model systems on NISQ devices, as a crucial step forward, has not been demonstrated yet. In this paper we showcase the first self-consistent hybrid quantum-classical calculations of the periodic Anderson model on Rigetti quantum devices, within the Gutzwiller variational embedding theoretical framework. It maps the infinite lattice problem to a quasi-particle Hamiltonian coupled to a quantum many-body embedding system, which is solved on quantum devices to overcome the classical exponential scaling in complexity. We show that the Gutzwiller hybrid quantum-classical embedding (GQCE) framework describes very well the quantum phase transitions from Kondo insulator to metal and from metal to Mott insulator in the correlated electron lattice model, with critical parameters at the phase boundaries accurately determined. The GQCE simulation framework, equipped with a full arsenal of evolving quantum algorithms to solve ground state and dynamics of quantum chemistry or equivalently finite embedding systems, is a well-adapted approach toward resolving complicated emergent properties in correlated condensed matter by exploiting NISQ technologies.
- arXiv:2003.04221 [pdf, other]
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Title: Ensemble switching: Critical behavior of probability in the switching measurements of superconducting nanobridgeSubjects: Superconductivity (cond-mat.supr-con); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Applied Physics (physics.app-ph)
We study correlated switchings of superconducting nanobridge probed with train of current pulses. For pulses with low repetition rate each pulse transits the superconducting bridge to normal state with probability $P$ independent of the outcomes in the preceding pulses. We show that with reduction of the time interval between pulses long range correlation between pulses occurs: stochastic switching in a single pulse rises temperature of the bridge and affects outcome of the probing for next pulses. As a result, an artificial intricate stochastic process with adjustable strength of correlation is produced. We identify regime where apparent switching probability exhibits the thermal hysteresis with discontinuity at a critical current amplitude of the probing pulse. This engineered stochastic process can be viewed as an artificial phase transition and provides an interesting framework for studying correlated systems. Due to its extreme sensitivity on the control parameter, i.e. electric current, temperature or magnetic field, it offers opportunity for ultra-sensitive detection.
- arXiv:2003.04224 [pdf]
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Title: Light-enhanced Charge Density Wave Coherence in a High-Temperature SuperconductorAuthors: S. Wandel, F. Boschini, E.H. da Silva Neto, L. Shen, M.X. Na, S. Zohar, Y. Wang, G.B. Welch, M.H. Seaberg, J.D. Koralek, G.L. Dakovski, W. Hettel, M-F. Lin, S.P. Moeller, W.F. Schlotter, A.H. Reid, M.P. Minitti, T. Boyle, F. He, R. Sutarto, R. Liang, D. Bonn, W. Hardy, R.A. Kaindl, D.G. Hawthorn, J.-S. Lee, A.F. Kemper, A. Damascelli, C. Giannetti, J.J. Turner, G. CoslovichComments: 13 pages, 3 figuresSubjects: Superconductivity (cond-mat.supr-con); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Strongly Correlated Electrons (cond-mat.str-el)
Quantum materials are often characterized by intertwined and competitive orders. The competition between superconductivity and charge density waves (CDW) in high-T$_{C}$ cuprates is a paradigmatic example. External tuning knobs, such as high-magnetic-fields and uniaxial strain, have been successfully employed to investigate their interaction. However, time-averaged steady-state experiments cannot capture the dynamical evolution of these quantum orders on the natural timescale of their interaction. Here we use ultrafast resonant soft X-ray scattering to track the transient evolution of CDW correlations in YBa$_{2}$Cu$_{3}$O$_{6+x}$ following the quench of superconductivity by an infrared laser pulse. The CDW order reacts to the quench of superconductivity on the picosecond timescale with a large enhancement of spatial coherence, nearly doubling the correlation length. We capture a CDW state which is profoundly non-thermal and distinct from the high-magnetic-field state observed in steady-state conditions. From this ultrafast snapshot we infer the existence of a superconductivity-induced phase modulation of CDW, yielding novel insight into the interaction between intertwined orders.
- arXiv:2003.04252 [pdf, other]
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Title: How ice grows: role of surface liquid films and water dropletsComments: 9 pages + 5 figures + supplementary material file + moviesSubjects: Chemical Physics (physics.chem-ph); Soft Condensed Matter (cond-mat.soft); Atmospheric and Oceanic Physics (physics.ao-ph); Fluid Dynamics (physics.flu-dyn); Geophysics (physics.geo-ph)
Close to the triple point, the surface of ice is covered by a thin liquid layer which crucially impacts growth and melting rates. Experimental probes cannot observe the growth processes below this layer, and classical models of growth by vapor deposition do not account for the formation of these wetting films. Here, we develop a mesoscopic model of liquid-film mediated ice growth, and identify the various resulting growth regimes. At low saturation, freezing proceeds by terrace spreading, but the motion of the buried solid is conveyed through the liquid to the outer liquid-vapor interface. At higher saturations water droplets condense, a large crater forms below, and freezing proceeds undetectable beneath the droplet. Our approach is a generalized framework that naturally models freezing close to three phase coexistence and provides a first principle theory of ice growth and melting that is much need in the geosciences.
- arXiv:2003.04256 [pdf, ps, other]
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Title: X-ray circular dichroism versus orbital magnetizationAuthors: Raffaele RestaComments: 6 pages, no figureJournal-ref: Phys. Rev. Research 2, 023139 (2020)Subjects: Materials Science (cond-mat.mtrl-sci)
The x-ray magnetic circular dichroism (XMCD) sum rule yields an extremely useful ground-state observable, which provides a quantitative measure of spontaneous time-reversal symmetry breaking (T-breaking) in a given material. I derive here its explicit expression within band-structure theory, in the general case: trivial insulators, topological insulators, and metals. Orbital magnetization provides a different measure of T-breaking in the electronic ground state. The two observables belong to the class of "geometrical" observables; both are local and admit a "density" in coordinate space. In both of them one could include/exclude selected groups of bands, in order to acquire element-specific information about the T-breaking material. Only in the case of an isolated flat band the contributions to the two observables coincide. Finally, I provide the corresponding geometrical formula-in a different Hilbert space-for a many-body interacting system.
- arXiv:2003.04269 [pdf, other]
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Title: Symmetric spin liquids on the stuffed honeycomb latticeComments: 14 pages, 11 figuresJournal-ref: Phys. Rev. B 101, 115103 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el)
We use a projective symmetry group analysis to determine all symmetric spin liquids on the stuffed honeycomb lattice Heisenberg model. This lattice interpolates between honeycomb, triangular and dice lattices, always preserving hexagonal symmetry, and it already has one spin liquid candidate, TbInO$_3$, albeit with strong spin-orbit coupling not considered here. In addition to the stuffed honeycomb lattice itself, we gain valuable insight into potential spin liquids on the honeycomb and triangular lattices, as well as how they might be connected. For example, the sublattice pairing state proposed on the honeycomb lattice connects to the uniform spinon Fermi surface that may be relevant for the triangular lattice with ring exchange, while there are no spin liquids competitive on both the $J_1-J_2$ honeycomb and triangular lattice limits. In particular, we find three stuffed honeycomb descendants of the U(1) Dirac spin liquid widely believed to be found on the $J_1-J_2$ triangular lattice. We also discuss how spin liquids near the honeycomb limit can potentially explain the physics of LiZn$_2$Mo$_3$O$_8$.
- arXiv:2003.04272 [pdf, other]
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Title: Floquet engineering magnetic materials with polarized and unpolarized lightComments: 6 + 6 pages, 4 + 2 figuresSubjects: Strongly Correlated Electrons (cond-mat.str-el)
Floquet engineering is a powerful tool to modify materials by coupling them to periodic light. Traditionally, amplitude and frequency are varied, but the polarization can be tuned to explore a larger phase space. We consider both polarized and several kinds of unpolarized light on insulating magnetic materials, showing that varied polarization protocols enhance different exchange couplings. As an illustration, we couple the triangular lattice Hubbard model at half-filling to periodic light with several polarizations and discuss how to alternately induce Dirac and chiral spin liquids.
- arXiv:2003.04277 [pdf, ps, other]
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Title: Vortex solutions in atomic Bose-Einstein condensates via the Adomian Decomposition MethodComments: 10 pages, 2 figures, accepted for publication in Romanian Reports in PhysicsSubjects: Quantum Gases (cond-mat.quant-gas); Classical Analysis and ODEs (math.CA)
We study the dynamics of vortices with arbitrary topological charges in weakly interacting Bose-Einstein condensates using the Adomian Decomposition Method to solve the nonlinear Gross-Pitaevskii equation in polar coordinates. The solutions of the vortex equation are expressed in the form of infinite power series. The power series representations are compared with the exact numerical solutions of the Gross-Pitaevskii equation for the uniform and the harmonic potential, respectively. We find that there is a good agreement between the analytical and the numerical results.
- arXiv:2003.04278 [pdf, ps, other]
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Title: Two More Fermionic Minimal ModelsAuthors: Justin KulpComments: 5 pages, 1 figureSubjects: High Energy Physics - Theory (hep-th); Statistical Mechanics (cond-mat.stat-mech); Strongly Correlated Electrons (cond-mat.str-el)
In this short note, we comment on the existence of two more fermionic unitary minimal models not included in recent work by Hsieh, Nakayama, and Tachikawa. These theories are obtained by fermionizing the $\mathbb{Z}_2$ symmetry of the m=11 and m=12 exceptional unitary minimal models. Furthermore, these should be the only missing cases.
- arXiv:2003.04284 [pdf, other]
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Title: Crystallization of interfacially tethered colloids in an emergent optofluidic potentialComments: 5 pages and 3 figuresSubjects: Soft Condensed Matter (cond-mat.soft); Statistical Mechanics (cond-mat.stat-mech)
The interplay between laser light, trapped particles, and fluid flow can produce counterintuitive effects in optical tweezing. Here we uncover an attractive, long-ranged, non-equilibrium force field centered on an optically trapped particle near a water-oil interface, produced by local heating and mediated by global fluid flow. This causes surrounding untrapped colloids, tethered to the interface but allowed to diffusely freely along it, to crystallize around the force center. In this configuration, the non-equilibrium force is the gradient of a potential, of strength proportional to the local heating, which, surprisingly, allows for an effective equilibrium description. Our results open unexplored routes to optofluidic manipulation and assembly of colloidal particles.
- arXiv:2003.04299 [pdf, other]
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Title: Discovering Symmetry Invariants and Conserved Quantities by Interpreting Siamese Neural NetworksSubjects: Computational Physics (physics.comp-ph); Disordered Systems and Neural Networks (cond-mat.dis-nn); Machine Learning (cs.LG)
In this paper, we introduce interpretable Siamese Neural Networks (SNN) for similarity detection to the field of theoretical physics. More precisely, we apply SNNs to events in special relativity, the transformation of electromagnetic fields, and the motion of particles in a central potential. In these examples, the SNNs learn to identify datapoints belonging to the same events, field configurations, or trajectory of motion. It turns out that in the process of learning which datapoints belong to the same event or field configuration, these SNNs also learn the relevant symmetry invariants and conserved quantities. These SNNs are highly interpretable, which enables us to reveal the symmetry invariants and conserved quantities without prior knowledge.
Replacements
- arXiv:1612.07468 (replaced) [pdf, other]
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Title: RNA substructure as a random matrix ensembleComments: 8 pages, 12 figures; v2: data set and figure added, comments added, references updated; v3: appendix and references added, few sentences including abstract paraphrased for clarification, remarks added in the conclusion; v4: published versionJournal-ref: Phys. Rev. E 100, 062404 (2019)Subjects: Quantitative Methods (q-bio.QM); Statistical Mechanics (cond-mat.stat-mech); High Energy Physics - Theory (hep-th); Biomolecules (q-bio.BM)
Combinatorial analysis of a certain abstract of RNA structures has been studied to investigate their statistics. Our approach regards the backbone of secondary structures as an alternate sequence of paired and unpaired sets of nucleotides, which can be described by random matrix model. We obtain the generating function of the structures using Hermitian matrix model with Chebyshev polynomial of the second kind and analyze the statistics with respect to the number of stems. To match the experimental findings of the statistical behavior, we consider the structures in a grand canonical ensemble and find a fugacity value corresponding to an appropriate number of stems.
- arXiv:1804.03285 (replaced) [pdf, other]
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Title: LLL and stochastic sandpile modelsSubjects: Number Theory (math.NT); Statistical Mechanics (cond-mat.stat-mech); Cryptography and Security (cs.CR)
Theaimofthepresentpaperistosuggestthatstatisticalphysicsprovides the correct language to understand the practical behavior of the LLL algorithm, most of which are left unexplained to this day. To this end, we propose sandpile models that imitate LLL with compelling accuracy, and prove for these models some of the most desired statements regarding LLL. We also formulate a few conjectures that formally capture our heuristics and would serve as milestones for further development of the theory.
- arXiv:1807.07259 (replaced) [pdf]
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Title: Zero-energy bound states in the high-temperature superconductors at the two-dimensional limitAuthors: Chaofei Liu, Cheng Chen, Xiaoqiang Liu, Ziqiao Wang, Yi Liu, Shusen Ye, Ziqiang Wang, Jiangping Hu, Jian WangJournal-ref: Science Advances 6, eaax7547 (2020)Subjects: Superconductivity (cond-mat.supr-con)
Majorana zero modes (MZMs) that obey the non-Abelian statistics have been intensively investigated for potential applications in topological quantum computing. The prevailing signals in tunneling experiments "fingerprinting" the existence of MZMs are the zero-energy bound states (ZEBSs). However, nearly all of the previously reported ZEBSs showing signatures of the MZMs are observed in difficult-to-fabricate heterostructures at very low temperatures and additionally require applied magnetic field. Here, by using in-situ scanning tunneling spectroscopy, we detect the ZEBSs upon the interstitial Fe adatoms deposited on two different high-temperature superconducting one-unit-cell-thick iron chalcogenides on SrTiO3(001). The spectroscopic results resemble the phenomenological characteristics of the MZMs inside the vortex cores of topological superconductors. Our experimental findings may extend the MZM explorations in connate topological superconductors towards an applicable temperature regime and down to the two-dimensional limit. While a concrete understanding of the observations is lacking, possible explanations involving novel 2D superconducting states with spin-orbit coupling, spontaneous nucleation of anomalous vortices at the magnetic sites, and noncoplanar magnetic ordering may further stimulate theoretical understandings of the scarcely captured ZEBSs in strongly correlated systems with multiband Cooper pairing.
- arXiv:1809.09031 (replaced) [pdf, other]
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Title: An ab initio perspective on scanning tunneling microscopy measurements of the tunable Kondo resonance of the TbPc$_2$ molecule on a gold substrateAuthors: Ivan I. Vrubel, Anastasiia A. Pervishko, Heike Herper, Barbara Brena, Olle Eriksson, Dmitry YudinComments: 8 pages, 5 figuresJournal-ref: Phys. Rev. B 101, 125106 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
With recent advances in the areas of nanostructure fabrication and molecular spintronics the idea of using single molecule magnets as building blocks for the next generation electronic devices becomes viable. A particular example represents a metal-organic complex in which organic ligands surround a rare-earth element or transition metal. Recently, it was explicitly shown that the relative position of the ligands with respect to each other can be reversibly changed by the external voltage without any need of the chemical modification of the sample. This opens a way of the electrical tuning of the Kondo effect in such metal-organic complexes. In this work, we present a detailed and systematic analysis of this effect in TbPc$_2$ from an ab initio perspective and compare the obtained results with the existing experimental data.
- arXiv:1811.01223 (replaced) [pdf, other]
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Title: Local stress analysis in Cu$_{50\%}$Zr$_{50\%}$ metallic glass under shear strain by means of first principle modelingComments: 9 pages, 5 figuresJournal-ref: I. Lobzenko, Y. Shiihara, T. Iwashita, and T. Egami, Phys. Rev. Lett. 124, 085503 (2020)Subjects: Materials Science (cond-mat.mtrl-sci)
Metallic glasses deform elastically under stress. However, the atomic-level origin of elastic properties of metallic glasses remain unclear. In this paper using {\em ab initio} molecular dynamics simulations of the Cu$_{50}$Zr$_{50}$ metallic glass under shear strain, we show that the heterogeneous stress relaxation results in the increased charge transfer from Zr to Cu atoms, enhancing the softening of the shear modulus. Changes in compositional short-range order and atomic position shifts due to the non-affine deformation are discussed. It is shown that the Zr subsystem exhibits a stiff behavior, whereas the displacements of Cu atoms from their initial positions, induced by the strain, provide the stress drop and softening.
- arXiv:1811.06967 (replaced) [pdf, other]
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Title: Adaptive Thouless--Anderson--Palmer equation for higher-order Markov random fieldsComments: 9 pages, 2 figures; Revised AppendixSubjects: Disordered Systems and Neural Networks (cond-mat.dis-nn); Statistical Mechanics (cond-mat.stat-mech)
The adaptive Thouless--Anderson--Palmer (TAP) mean-field approximation is one of the advanced mean-field approaches, and it is known as a powerful accurate method for Markov random fields (MRFs) with quadratic interactions (pairwise MRFs). In this study, an extension of the adaptive TAP approximation for MRFs with many-body interactions (higher-order MRFs) is developed. We show that the adaptive TAP equation for pairwise MRFs is derived by naive mean-field approximation with diagonal consistency. Based on the equivalence of the approximate equation obtained from the naive mean-field approximation with diagonal consistency and the adaptive TAP equation in pairwise MRFs, we formulate approximate equations for higher-order Boltzmann machines, which is one of simplest higher-order MRFs, via the naive mean-field approximation with diagonal consistency.
- arXiv:1901.06516 (replaced) [pdf, ps, other]
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Title: The adaptive interpolation method for proving replica formulas. Applications to the Curie-Weiss and Wigner spike modelsSubjects: Disordered Systems and Neural Networks (cond-mat.dis-nn); Information Theory (cs.IT); Mathematical Physics (math-ph); Probability (math.PR)
In this contribution we give a pedagogic introduction to the newly introduced adaptive interpolation method to prove in a simple and unified way replica formulas for Bayesian optimal inference problems. Many aspects of this method can already be explained at the level of the simple Curie-Weiss spin system. This provides a new method of solution for this model which does not appear to be known. We then generalize this analysis to a paradigmatic inference problem, namely rank-one matrix estimation, also refered to as the Wigner spike model in statistics. We give many pointers to the recent literature where the method has been succesfully applied.
- arXiv:1901.08546 (replaced) [pdf, other]
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Title: Ballistic and hydrodynamic magnetotransport in narrow channelsAuthors: Tobias Holder, Raquel Queiroz, Thomas Scaffidi, Navot Silberstein, Asaf Rozen, Joseph A. Sulpizio, Lior Ella, Shahal Ilani, Ady SternComments: 13+3 pages, 11 figuresJournal-ref: Phys. Rev. B 100, 245305 (2019)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Strongly Correlated Electrons (cond-mat.str-el)
An increasing number of low carrier density materials exhibit a surprisingly large transport mean free path due to inefficient momentum relaxation. Consequently, charge transport in these systems is markedly non-ohmic but rather ballistic or hydrodynamic, features which can be explored by driving current through narrow channels. Using a kinetic equation approach we theoretically investigate how a non-quantizing magnetic field discerns ballistic and hydrodynamic transport, in particular in the spatial dependence of the transverse electric field, $E_y$: We find that $E_y$ is locally enhanced when the flow exhibits a sharp directional anisotropy in the non-equilibrium density. As a consequence, at weak magnetic fields, the curvature of $E_y$ has opposite signs in the ballistic and hydrodynamic regimes. Moreover, we find a robust signature of the onset of non-local correlations in the form of distinctive peaks of the transverse field, which are accessible by local measurements. Our results demonstrate that a purely hydrodynamic approach is insufficient in the Gurzhi regime once a magnetic field is introduced.
- arXiv:1903.06094 (replaced) [pdf, other]
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Title: Observation of a Correlation Between Internal friction and Urbach Energy in Amorphous Oxides Thin FilmsAuthors: Alex Amato, Silvana Terreni, Massimo Granata, Christophe Michel, Benoit Sassolas, Laurent Pinard, Maurizio Canepa, Gianpietro CagnoliJournal-ref: Sci Rep 10, 1670 (2020)Subjects: Optics (physics.optics); Disordered Systems and Neural Networks (cond-mat.dis-nn)
We have investigated by spectroscopic ellipsometry (SE, 190-1700 nm) the optical properties of uniform, amorphous thin films of Ta2O5 and Nb2O5 as deposited and after annealing, and after so-called "doping" with Ti atoms which leads to mixed oxides. Ta2O5 and Ti:Ta2O5 are currently used as high-index components in Bragg reflectors for Gravitational Wave Detectors. Parallel to the optical investigation, we measured the mechanical energy dissipation of the same coatings, through the so-called "loss angle" phi = Q^-1, which quantifies the energy loss in materials. By applying the well-known Cody-Lorentz model in the analysis of SE data we have been able to derive accurate information on the fundamental absorption edge through important parameters related to the electronic density of states, such as the optical gap (E_g) and the energy width of the exponential Urbach tail (the Urbach energy E_U). We have found that E_U is neatly reduced by suitable annealing as is also perceptible from direct inspection of SE data. Ti-doping also points to a minor decrease of E_U. The reduction of E_U parallels a lowering of the mechanical losses quantified by the loss angle phi. The correlation highlights that both the electronic states responsible of Urbach tail and the internal friction are sensitive to a self-correlation of defects on a medium-range scale, which is promoted by annealing and in our case, to a lesser extent, by doping. These observations may contribute to a better understanding of the relationship between structural and mechanical properties in amorphous oxides.
- arXiv:1904.13160 (replaced) [pdf, other]
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Title: Magnetism trends in doped Ce-Cu intermetallics in the vicinity of quantum criticality: realistic Kondo lattice models based on dynamical mean-field theoryAuthors: Munehisa MatsumotoComments: 12 pages, 5 figures, to appear in Phys. Rev. MaterialsJournal-ref: Phys. Rev. Materials 4, 054401 (2020)Subjects: Materials Science (cond-mat.mtrl-sci); Strongly Correlated Electrons (cond-mat.str-el)
The quantum critical point (QCP) in the archetypical heavy-fermion compound CeCu$_6$ doped by Au is described, accounting for the localized $4f$-electron of Ce, using realistic electronic structure calculations combined with dynamical mean-field theory (DMFT). Magnetism trends in Ce(Cu$_{1-\epsilon}$Au$_\epsilon$)$_6$ are compared with those in Co-doped CeCu$_{5}$, which resides on the non-ferromagnetic side of the composition space of one of the earliest rare-earth permanent magnet compounds, Ce(Co,Cu)$_5$. The construction of a realistic Doniach phase diagram shows that the system crosses over a magnetic quantum critical point in the Kondo lattice in $0.2<x<0.4$ of Ce(Cu$_{1-x}$Co$_x$)$_5$. Comparison between Au-doped CeCu$_6$ and Co-doped CeCu$_5$ reveals that the swept region in the vicinity of QCP for the latter thoroughly covers that of the former. The implications of these trends on the coercivity of the bulk rare-earth permanent magnets are discussed.
- arXiv:1905.02070 (replaced) [pdf, other]
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Title: Finite-time adiabatic processes: derivation and speed limitComments: Main text: 5 pages; 18 pages with appendices and references; major revision with results for a general non-linear potential and study of fluctuations added; Physical Review E in pressJournal-ref: Phys. Rev. E 101, 032129 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Statistical Mechanics (cond-mat.stat-mech)
Obtaining adiabatic processes that connect equilibrium states in a given time represents a challenge for mesoscopic systems. In this paper, we explicitly show how to build these finite-time adiabatic processes for an overdamped Brownian particle in an arbitrary potential, a system that is relevant both at the conceptual and the practical level. This is achieved by jointly engineering the time evolutions of the binding potential and the fluid temperature. Moreover, we prove that the second principle imposes a speed limit for such adiabatic transformations: there appears a minimum time to connect the initial and final states. This minimum time can be explicitly calculated for a general compression/decompression situation.
- arXiv:1905.09168 (replaced) [pdf, other]
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Title: Predicting quantum many-body dynamics with transferable neural networksAuthors: Zewang Zhang, Shuo Yang, Yi-hang Wu, Chenxi Liu, Yimin Han, Ching Hua Lee, Zheng Sun, Guangjie Li, Xiao ZhangComments: 6 figures, 1 table, 8 pagesSubjects: Statistical Mechanics (cond-mat.stat-mech); Strongly Correlated Electrons (cond-mat.str-el); Computational Physics (physics.comp-ph); Quantum Physics (quant-ph)
Machine learning (ML) architectures such as convolutional neural networks (CNNs) have garnered considerable recent attention in the study of quantum many-body systems. However, advanced ML approaches such as transfer learning have seldom been applied to such contexts. Here we demonstrate that a simple recurrent unit (SRU) based efficient and transferable sequence learning framework is capable of learning and accurately predicting the time evolution of one-dimensional (1D) Ising model with simultaneous transverse and parallel magnetic fields, as quantitatively corroborated by relative entropy measurements and magnetization between the predicted and exact state distributions. At a cost of constant computational complexity, a larger many-body state evolution was predicted in an autoregressive way from just one initial state, without any guidance or knowledge of any Hamiltonian. Our work paves the way for future applications of advanced ML methods in quantum many-body dynamics only with knowledge from a smaller system.
- arXiv:1905.11514 (replaced) [pdf, other]
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Title: Solid-like mean-square displacement in glass-forming liquidsJournal-ref: J. Chem. Phys. 152, 141101 (2020)Subjects: Soft Condensed Matter (cond-mat.soft); Materials Science (cond-mat.mtrl-sci); Statistical Mechanics (cond-mat.stat-mech)
It was recently shown that the real part of the frequency-dependent fluidity for several glass-forming liquids of different chemistry conforms to the prediction of the random barrier model (RBM) devised for ac electrical conduction in disordered solids [S. P. Bierwirth \textit{et al.}, Phys. Rev. Lett. {\bf 119}, 248001 (2017)]. Inspired by these results we introduce a crystallization-resistant modification of the Kob-Andersen binary Lennard-Jones mixture for which the results of extensive graphics-processing unit (GPU)-based molecular-dynamics simulations are presented. We find that the low-temperature mean-square displacement is fitted well by the RBM prediction, which involves no shape parameters. This finding highlights the challenge of explaining why a simple model based on hopping of non-interacting particles in a fixed random energy landscape can reproduce the complex and highly cooperative dynamics of glass-forming liquids.
- arXiv:1906.08028 (replaced) [pdf]
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Title: Up to 70 THz bandwidth from implanted Ge photoconductive antenna excited by a fibre laserAuthors: Abhishek Singh, Alexej Pashkin, Stephan Winnerl, Malte Welsch, Cornelius Beckh, Philipp Sulzer, Alfred Leitenstorfer, Manfred Helm, Harald SchneiderJournal-ref: Light Sci Appl 9, 30 (2020)Subjects: Optics (physics.optics); Materials Science (cond-mat.mtrl-sci)
Phase-stable electromagnetic pulses in the THz frequency range offer several unique capabilities in time-resolved spectroscopy. However, the diversity of their application is limited by the covered spectral bandwidth. In particular, the upper frequency limit of photoconductive emitters - the most widespread technique in THz spectroscopy - reaches only up to 7 THz in regular transmission mode due to the absorption by infrared-active optical phonons. Here, we present ultra-broadband (extending up to 70 THz) THz emission from Au implanted Ge emitter which is compatible with a fibre laser operating at 1.1 and 1.55 {\mu}m wavelengths at a repetition rates of 10 and 20 MHz, respectively. This opens a perspective for the development of compact THz photonic devices operating up to multi-THz frequencies and compatible with Si CMOS technology.
- arXiv:1906.11131 (replaced) [pdf, ps, other]
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Title: Light scattering as a Poisson process and first-passage probabilityComments: 16 pages, 5 figures, to be published in Journal of Statistical Mechanics: theory and experiment. This is the accepted version with additional figures and clarifications based on referees' reportsSubjects: Statistical Mechanics (cond-mat.stat-mech)
A particle entering a scattering and absorbing medium executes a random walk through a sequence of scattering events. The particle ultimately achieves first-passage, leaving the medium or it is absorbed. The Kubelka-Munk model describes a flux of particles moving perpendicular to the surface of a plane-parallel medium. The particle path alternates between the positive direction into the medium and the negative direction back towards the surface. Backscattering events from the positive to the negative direction occur at local maxima or peaks, while backscattering from the negative to the positive direction occur at local minima or valleys. The probability of a particle avoiding absorption as it follows its path decreases exponentially with the path-length \(\lambda\). The reflectance of a semi-infinite slab is therefore the Laplace transform of the distribution of path-length that ends with a first-passage out of the medium. In the case of a constant scattering rate the random walk is a Poisson process. We verify our results with two iterative calculations, one using the properties of iterated convolution with a symmetric kernel and the other via direct calculation with an exponential step-length distribution.
We present a novel demonstration, based on fluctuation theory of sums of random variables, that the first-passage probability as a function of the number of peaks in the alternating path is a step-length distribution-free combinatoric expression. Counting paths with backscattering on the real half-line results in the same Catalan number coefficients as Dyck paths on the whole numbers. Including a separate forward-scattering Poisson process results in an expression related to counting Motzkin paths. We therefore connect walks on the real line to discrete path combinatorics. - arXiv:1906.12090 (replaced) [pdf, other]
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Title: Chromosome contact maps are bifractalComments: 21 pages, 3 figuresSubjects: Biomolecules (q-bio.BM); Statistical Mechanics (cond-mat.stat-mech); Biological Physics (physics.bio-ph)
Modern biological techniques such as Hi--C permit to measure probabilities that different chromosomal regions are close in space. These probabilities can be visualised as matrices called contact maps. Contact maps are characterized by self-similar blocks along the diagonal, corresponding to a hierarchy of tightly packed chromosomal domains. Statistical properties of these maps, and thus of chromosomal interactions, are usually summarized by the scaling of the contact probability as a function of the genomic distance. This approach is fraught with limitations, since such scaling is usually rather noisy. Here, we introduce a multifractal analysis of chromosomal contact maps. Our analysis reveals that Hi--C maps are bifractal, i.e. they are complex geometrical objects characterized by two distinct fractal dimensions. To rationalize this observation, we introduce a model that describes chromosomes as a hierarchical set of domains nested in each other and we solve it exactly. The predicted multifractal spectrum is in excellent quantitative agreement with experimental data. Our theory yields to a more robust estimation of the scaling exponent of the contact probability than existing methods. By applying this method to experimental data, we detect subtle conformational changes among chromosomes during differentiation of human stem cells.
- arXiv:1907.02041 (replaced) [pdf, ps, other]
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Title: Anisotropy of spin-transfer torques and Gilbert damping induced by Rashba couplingComments: 20 pages, 4 figuresJournal-ref: Phys. Rev. B 101, 085405 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Spin-transfer torques (STT), Gilbert damping (GD), and effective spin renormalization (ESR) are investigated microscopically in a 2D Rashba ferromagnet with spin-independent Gaussian white-noise disorder. Rashba spin-orbit coupling induced anisotropy of these phenomena is thoroughly analysed. For the case of two partly filled spin subbands, a remarkable relation between the anisotropic STT, GD, and ESR is established. In the absence of magnetic field and other torques on magnetization, this relation corresponds to a current-induced motion of a magnetic texture with the classical drift velocity of conduction electrons. Finally, we compute spin susceptibility of the system and generalize the notion of spin-polarized current.
- arXiv:1907.04094 (replaced) [pdf, other]
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Title: Classical and quantum chaos in a three-mode bosonic systemComments: 13 pages, 6 figures, v2: Sec. IV.C revised and extended. Appendix on truncated Wigner simulations added. v3: added new method for calculation of classical Lyapunov exponents, discussion of OTOCs updated, wording changesJournal-ref: Phys. Rev. A 101, 053604 (2020)Subjects: Quantum Physics (quant-ph); Quantum Gases (cond-mat.quant-gas)
We study the dynamics of a three-mode bosonic system with mode-changing interactions. For large mode occupations the short-time dynamics is well described by classical mean-field equations allowing us to study chaotic dynamics in the classical system and its signatures in the corresponding quantum dynamics. By introducing a symmetry-breaking term we tune the classical dynamics from integrable to strongly chaotic which we demonstrate by calculating Poincar\'e sections and Lyapunov exponents. The corresponding quantum system features level statistics that change from Poissonian in the integrable to Wigner-Dyson in the chaotic case. We investigate the behavior of out-of-time-ordered correlators (OTOCs), specifically the squared commutator, for initial states located in regular and chaotic regions of the classical mixed phase space and find marked differences between the two cases. The short-time behavior is well captured by semi-classical truncated Wigner simulations directly relating these features to properties of the underlying classical mean field dynamics. We discuss a possible experimental realization of this model system in a Bose-Einstein condensate of rubidium atoms which allows reversing the sign of the Hamiltonian required for measuring OTOCs experimentally.
- arXiv:1907.05665 (replaced) [pdf]
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Title: Structure, Stability and Mechanical Properties of Boron-Rich Mo-B Phases: A Computational StudyComments: 25 pages, 5 figures, 3 Tables, Supporting information (5 pages)Subjects: Materials Science (cond-mat.mtrl-sci); Computational Physics (physics.comp-ph)
Molybdenum borides were studied theoretically using first-principles calculations, empirical total energy model and global optimization techniques to determine stable crystal structures. Our calculations reveal the structures of known Mo-B phases, attaining close agreement with experiment. Following our developed lattice model, we describe in detail the crystal structure of boron-rich $MoB_x$ phases with 3<x<9 as the hexagonal $P6_3/mmc$-$MoB_3$ structure with Mo atoms partially replaced by triangular boron units. The most energetically stable arrangement of these $B_3$ units corresponds to their uniform distribution in the bulk of the crystal structure, which leads to the formation of a disordered nonstoichiometric phase, with ordering arising at compositions close to x=5 due to a strong repulsive interaction between neighboring $B_3$ units. The most energetically favorable structures of $MoB_x$ correspond to the compositions 4<x<5, with $MoB_5$ being the boron-richest stable phase. The estimated hardness of $MoB_5$ is 37-39 GPa, suggesting that the boron-rich phases are potentially superhard.
- arXiv:1907.09037 (replaced) [pdf, other]
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Title: Crystal elasto-plasticity on the Poincaré half-planeComments: 24 pages, 4 figuresSubjects: Materials Science (cond-mat.mtrl-sci); Soft Condensed Matter (cond-mat.soft)
We explore the nonlinear variational modelling of two-dimensional (2D) crystal plasticity based on strain energies which are invariant under the full symmetry group of 2D lattices. We use a natural parameterization of strain space via the upper complex Poincar\'e half-plane. This transparently displays the constraints imposed by lattice symmetry on the energy landscape. Quasi-static energy minimization naturally induces bursty plastic flow and shape change in the crystal due to the underlying coordinated basin-hopping local strain activity. This is mediated by the nucleation, interaction, and annihilation of lattice defects occurring with no need for auxiliary hypotheses. Numerical simulations highlight the marked effect of symmetry on all these processes. The kinematical atlas induced by symmetry on strain space elucidates how the arrangement of the energy extremals and the possible bifurcations of the strain-jump paths affect the plastification mechanisms and defect-pattern complexity in the lattice.
- arXiv:1907.09281 (replaced) [pdf, ps, other]
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Title: Numerical study of the transverse localization of waves in one-dimensional lattices with randomly distributed gain and loss: Effect of disorder correlationsComments: 16 pages, 9 figuresJournal-ref: Waves in Random and Complex Media 30, 1774680 (2020)Subjects: Disordered Systems and Neural Networks (cond-mat.dis-nn); Optics (physics.optics)
We study numerically the effects of short- and long-range correlations on the localization properties of the eigenstates in a one-dimensional disordered lattice characterized by a random non-Hermitian Hamiltonian, where the imaginary part of the on-site potential is random. We calculate participation number versus strengths of disorder and correlation. In the short-ranged case and when the correlation length is sufficiently small, we find that there exists a critical value of the disorder strength, below which enhancement and above which suppression of localization occurs as the correlation length increases. In the region where the correlation length is larger, localization is suppressed in all cases. A similar behavior is obtained for long-range correlations as the disorder strength and the correlation exponent are varied. Unlike in the case of a long-range correlated real random potential, no signature of the localization transition is found in a long-range correlated imaginary random potential. In the region where localization is enhanced in the presence of long-range correlations, we find that the enhancement occurs in the whole energy band, but is strongest near the band center. In addition, we find that the anomalous localization enhancement effect occurs near the band center in the long-range correlated case.
- arXiv:1907.09947 (replaced) [pdf]
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Title: High-Chern-Number and High-Temperature Quantum Hall Effect without Landau LevelsSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
The quantum Hall effect (QHE) with quantized Hall resistance of h/{\nu}e2 starts the research on topological quantum states and lays the foundation of topology in physics. Afterwards, Haldane proposed the QHE without Landau levels, showing nonzero Chern number |C|=1, which has been experimentally observed at relatively low temperatures. For emerging physics and low-power-consumption electronics, the key issues are how to increase the working temperature and realize high Chern numbers (C>1). Here, we report the experimental discovery of high-Chern-number QHE (C=2) without Landau levels and C=1 Chern insulator state displaying nearly quantized Hall resistance plateau above the N\'eel temperature in MnBi2Te4 devices. Our observations provide a new perspective on topological matter and open new avenues for exploration of exotic topological quantum states and topological phase transitions at higher temperatures.
- arXiv:1907.10934 (replaced) [pdf]
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Title: Soft Granular Particles Sheared at a Controlled Volume: Flow Curves and Multiple Timescales of RelaxationSubjects: Soft Condensed Matter (cond-mat.soft)
We study the responses of fluid-immersed soft hydrogel spheres to both steady shearing and cyclic cessations. The slippery, deformable particles along with the density-matched interstitial fluid are sandwiched between two opposing rough cones, allowing the rheological measurements for volume fractions ranging from 0.73 to 0.27. Steady-state flow curves and shear-to-normal stress ratios reveal nontrivial trends over the decrease of volume fraction. They reflect a solid-to-fluid transition as the system becomes a suspension, with the Reynolds number slightly above unity. In addition, experiments with cyclic shearing and cessations at high volume fractions, accompanied by refractive index-matched internal imaging, establish the connection between stress relaxation and particle rearrangement. Our studies also include the long-time relaxation of the packing as well as that of a single particle. These results demonstrate a multitude of relaxation timescales behind the dynamics of soft particles, and provoke questions on how we extend existing paradigms on the flow of a densely packed system when the softness is actively involved.
- arXiv:1907.11333 (replaced) [pdf, other]
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Title: Entanglement Area Law for Shallow and Deep Quantum Neural Network StatesJournal-ref: New Journal of Physics, Volume 22, May 2020Subjects: Quantum Physics (quant-ph); Strongly Correlated Electrons (cond-mat.str-el); Computational Physics (physics.comp-ph)
A study of the artificial neural network representation of quantum many-body states is presented. The locality and entanglement properties of states for shallow and deep quantum neural networks are investigated in detail. By introducing the notion of local quasi-product states, for which the locally connected shallow feed-forward neural network states and restricted Boltzmann machine states are special cases, we show that R\'{e}nyi entanglement entropies of all these states obey the entanglement area law. Besides, we also investigate the entanglement features of deep Boltzmann machine states and show that locality constraints imposed on the neural networks make the states obey the entanglement area law. Finally, as an application, we apply the notion of R\'{e}nyi entanglement entropy to understanding the power of neural networks and show that image classification problems which can be efficiently solved must obey the area law.
- arXiv:1908.01857 (replaced) [pdf, other]
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Title: High-precision local transfer of van der Waals materials on nanophotonic structuresComments: 9 pages, 5 figuresSubjects: Applied Physics (physics.app-ph); Materials Science (cond-mat.mtrl-sci); Optics (physics.optics)
Prototyping of van der Waals materials on dense nanophotonic devices requires high-precision monolayer discrimination to avoid bulk material contamination. We use the glass transition temperature of polycarbonate, used in the standard dry transfer process, to draw an in situ point for the precise pickup of two dimensional materials. We transfer transition metal dichalcogenide monolayers onto a large-area silicon nitride spiral waveguide and silicon nitride ring resonators to demonstrate the high-precision contamination-free nature of the modified dry transfer method. Our improved local transfer technique is a necessary step for the deterministic integration of high-quality van der Waals materials onto nanocavities for the exploration of few-photon nonlinear optics on a high-throughput, nanofabrication-compatible platform.
- arXiv:1908.03516 (replaced) [pdf]
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Title: Experimental Demonstration of an Extreme Sub-Wavelength Nanomagnetic Acoustic Antenna Actuated by Spin-Orbit Torque from a Heavy Metal NanostripJournal-ref: Advanced Materials Technologies, 1901076 (2020)Subjects: Applied Physics (physics.app-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
A novel on-chip extreme sub-wavelength "acoustic antenna" whose radiation efficiency is ~50 times larger than the theoretical limit for a resonantly driven antenna is demonstrated. The antenna is composed of magnetostrictive nanomagnets deposited on a piezoelectric substrate. The nanomagnets are partially in contact with a heavy metal (Pt) nanostrip. Passage of alternating current through the nanostrip exerts alternating spin-orbit torque on the nanomagnets and periodically rotates their magnetizations. During the rotation, the magnetostrictive nanomagnets expand and contract, thereby setting up alternating tensile and compressive strain in the piezoelectric substrate underneath. This leads to the generation of a surface acoustic wave in the substrate and makes the nanomagnet assembly act as an acoustic antenna. The measured radiation efficiency of this acoustic antenna at the detected frequency is ~1%, while the wavelength to antenna dimension ratio is ~ 67:1. For a standard antenna driven at acoustic resonance, the efficiency would have been limited to ~ (1/67)^2 = 0.02%. It was possible to beat that limit (by ~50 times) via actuating the antenna not by acoustic resonance, but by using a completely different mechanism involving spin-orbit torque originating from the giant spin Hall effect in Pt.
- arXiv:1908.09217 (replaced) [pdf, ps, other]
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Title: Manifolds in high dimensional random landscape: complexity of stationary points and depinningJournal-ref: Phys. Rev. E 101, 020101 (2020)Subjects: Disordered Systems and Neural Networks (cond-mat.dis-nn); Statistical Mechanics (cond-mat.stat-mech); Mathematical Physics (math-ph)
We obtain explicit expressions for the annealed complexities associated respectively with the total number of (i) stationary points and (ii) local minima of the energy landscape for an elastic manifold with internal dimension $d<4$ embedded in a random medium of dimension $N \gg 1$ and confined by a parabolic potential with the curvature parameter $\mu$. These complexities are found to both vanish at the critical value $\mu_c$ identified as the Larkin mass. For $\mu<\mu_c$ the system is in complex phase corresponding to the replica symmetry breaking in its $T=0$ thermodynamics. The complexities vanish respectively quadratically (stationary points) and cubically (minima) at $\mu_c^-$. For $d\geq 1$ they admit a finite "massless" limit $\mu=0$ which is used to provide an upper bound for the depinning threshold under an applied force.
- arXiv:1908.11362 (replaced) [pdf, ps, other]
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Title: Spin-1/2 XXZ Heisenberg chain in a longitudinal magnetic fieldComments: 10 pages (9 pages in a journal version), 7 multi-panel figures, 1 tableJournal-ref: Phys. Rev. B 100, 134434 (2019)Subjects: Strongly Correlated Electrons (cond-mat.str-el); Statistical Mechanics (cond-mat.stat-mech)
We study the XXZ Heisenberg model in a longitudinal magnetic field using a tensor renormalization method. Built into the tensor representation of the XXZ model is the U(1) symmetry, which is systematically maintained at each renormalization step. This enables rather large tensor representations. We extract ground state properties as well as the low lying spectrum from the fixed point tensors. With rather moderate numerical effort we achieve a very good accuracy as demonstrated by comparison with Bethe Ansatz calculations. The phase structure of the model can be accurately reproduced just from the largest fixed point tensor elements.
- arXiv:1909.03412 (replaced) [pdf, other]
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Title: Evolution of the magnetic and polaronic order of $\rm{Pr_{1/2}Ca_{1/2}MnO_3}$ following an ultrashort light pulseComments: 26 pages, 32 figuresSubjects: Strongly Correlated Electrons (cond-mat.str-el); Materials Science (cond-mat.mtrl-sci)
The dynamics of electrons, spins and phonons induced by optical femtosecond pulses has been simulated for the polaronic crystal $\rm{Pr_{1/2}Ca_{1/2}MnO_3}$. The model used for the simulation has been derived from first-principles calculations. The simulations reproduce the experimentally observed melting of charge/orbital order with increasing fluence. The loss of charge order in the high-fluence regime induces a transition to a ferromagnetic metal. At low fluence, the dynamics is deterministic and coherent phonons are created by the repopulation of electronic orbitals, which are strongly coupled to the phonon degrees of freedom. In contrast to the low-fluence regime, the magnetic transitions occurring at higher fluence can be attributed to a quasi-thermal transition of a cold-plasma-like state with hot electrons and cold phonons and spins. The findings can be rationalized in a more complete picture of the electronic structure that goes beyond the simple ionic picture of charge order.
- arXiv:1909.04156 (replaced) [pdf]
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Title: Tunable control over InSb(110) surface conductance utilizing charged adatomsAuthors: Sara M. Mueller, Dongjoon Kim, Stephen R. McMillan, Steven J. Tjung, Jacob J. Repicky, Stephen Gant, Evan Lang, Fedor Bergmann, Kevin Werner, Enam Chowdhury, Aravind Asthagiri, Michael E. Flatte, Jay A. GuptaComments: 15 pages, 6 figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We report scanning tunneling microscopy studies of individual adatoms on an InSb(110) surface. The adatoms can be reproducibly dropped off from the tip by voltage pulses, and exhibit pronounced changes in contrast as a function of imaging conditions such as bias voltage, STM set current and under photoillumination. Analysis of the apparent height in STM images suggests this behavior reflects tip-induced ionization of a (+/0) charge transition level, with tunneling rates that are sensitive functions of tip position, bias voltage, set current and surface photovoltage. The adatom ionization effect extends greater than 50 nm away, reflecting the low concentration and binding energy of the residual donors in the InSb crystal. The experimental data are in good agreement with density functional theory calculations, and two-level transport modeling. These studies demonstrate how individual atoms can be used to sensitively control current flow in future nanoscale devices.
- arXiv:1910.00146 (replaced) [pdf, other]
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Title: High-harmonic generation by electric polarization, spin current, and magnetizationComments: 16 pages, 10 figuresJournal-ref: Phys. Rev. B 100, 214424 (2019)Subjects: Strongly Correlated Electrons (cond-mat.str-el); Optics (physics.optics); Quantum Physics (quant-ph)
High-harmonic generation (HHG), a typical nonlinear optical effect, has been actively studied in electron systems such as semiconductors and superconductors. As a natural extension, we theoretically study HHG from electric polarization, spin current and magnetization in magnetic insulators under terahertz (THz) or gigahertz (GHz) electromagnetic waves. We use simple one-dimensional spin chain models with or without multiferroic coupling between spins and the electric polarization, and study the dynamics of the spin chain coupled to an external ac electric or magnetic field. We map spin chains to two-band fermions and invoke an analogy of semiconductors and superconductors. With a quantum master equation and Lindblad approximation, we compute the time evolution of the electric polarization, spin current, and magnetization, showing that they exhibit clear harmonic peaks. We also show that the even-order HHG by magnetization dynamics can be controlled by static magnetic fields in a wide class of magnetic insulators. We propose experimental setups to observe these HHG, and estimate the required strength of the ac electric field $E_0$ for detection as $E_0\sim100$kV/cm--1MV/cm, which corresponds to the magnetic field $B_0\sim0.1$T--1T. The estimated strength would be relevant also for experimental realizations of other theoretically-proposed nonlinear optical effects in magnetic insulators such as Floquet engineering of magnets.
- arXiv:1910.02882 (replaced) [pdf, other]
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Title: Anisotropic particles in two-dimensional convective turbulenceComments: manuscript + additional materialsJournal-ref: Phys. Fluids 32, 023305 (2020)Subjects: Soft Condensed Matter (cond-mat.soft); Fluid Dynamics (physics.flu-dyn)
The orientational dynamics of inertialess anisotropic particles transported by two-dimensional convective turbulent flows display a coexistence of regular and chaotic features. We numerically demonstrate that very elongated particles (rods) align preferentially with the direction of the fluid flow, i.e., horizontally close to the isothermal walls and dominantly vertically in the bulk. This behaviour is due to the the presence of a persistent large scale circulation flow structure, which induces strong shear at wall boundaries and in up/down-welling regions. The near-wall horizontal alignment of rods persists at increasing the Rayleigh number, while the vertical orientation in the bulk is progressively weakened by the corresponding increase of turbulence intensity. Furthermore, we show that very elongated particles are nearly orthogonal to the orientation of the temperature gradient, an alignment independent of the system dimensionality and which becomes exact only in the limit of infinite Prandtl number. Tumbling rates are extremely vigorous adjacent to the walls, where particles roughly perform Jeffery orbits. This implies that the root-mean-square near-wall tumbling rates for spheres are much stronger than for rods, up to $\mathcal{O}(10)$ times at $Ra\simeq 10^9$. In the turbulent bulk the situation reverses and rods tumble slightly faster than isotropic particles, in agreement with earlier observations in two-dimensional turbulence.
- arXiv:1910.06336 (replaced) [pdf, other]
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Title: Systematic Constructions of Fracton TheoriesAuthors: Djordje RadicevicComments: 41 pages, 8 figures. v2: minor clarifications and references added. v3: expanded discussion of models on BCC lattices and with nonabelian symmetries, further minor clarifications and reference additionsSubjects: Strongly Correlated Electrons (cond-mat.str-el); High Energy Physics - Lattice (hep-lat); High Energy Physics - Theory (hep-th)
Fracton theories possess exponentially degenerate ground states, excitations with restricted mobility, and nontopological higher-form symmetries. This paper shows that such theories can be defined on arbitrary spatial lattices in three dimensions. The key element of this construction is a generalization of higher-form gauge theories to so-called $\mathfrak{F}_p$ gauge theories, in which gauge transformations of rank-$k$ fields are specified by rank-$(k - p)$ gauge parameters. The $\mathbb{Z}_2$ rank-two theory of type $\mathfrak{F}_2$, placed on a cubic lattice and coupled to scalar matter, is shown to have a topological phase exactly dual to the well-known X-cube model. Generalizations of this example yield novel fracton theories. In the continuum, the $\mathrm{U}(1)$ rank-two theory of type $\mathfrak{F}_2$ is shown to have a perturbatively gapless fracton regime that cannot be consistently interpreted as a tensor gauge theory of any kind. The compact scalar fields that naturally couple to this $\mathfrak{F}_2$ theory also show gapless fracton behavior; on a cubic lattice they have a conserved $\mathrm{U}(1)$ charge and dipole moment, but these particular charges are not necessarily conserved on more general lattices. The construction straightforwardly generalizes to $\mathfrak{F}_2$ theories of nonabelian rank-two gauge fields, giving first examples of pure nonabelian higher-rank theories.
- arXiv:1910.07540 (replaced) [pdf, other]
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Title: Phase diagram and dynamics of the SU($\boldsymbol N$) symmetric Kondo lattice modelComments: 12+ pages + appendices; 13 figuresJournal-ref: Phys. Rev. Research 2, 013276 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el)
In heavy-fermion systems, the competition between the local Kondo physics and intersite magnetic fluctuations results in unconventional quantum critical phenomena which are frequently addressed within the Kondo lattice model (KLM). Here we study this interplay in the SU($N$) symmetric generalization of the two-dimensional half-filled KLM by quantum Monte Carlo simulations with $N$ up to 8. While the long-range antiferromagnetic (AF) order in SU($N$) quantum spin systems typically gives way to spin-singlet ground states with spontaneously broken lattice symmetry, we find that the SU($N$) KLM is unique in that for each finite $N$ its ground-state phase diagram hosts only two phases -- AF order and the Kondo-screened phase. The absence of any intermediate phase between the $N=2$ and large-$N$ cases establishes adiabatic correspondence between both limits and confirms that the large-$N$ theory is a correct saddle point of the KLM fermionic path integral and a good starting point to include quantum fluctuations. In addition, we determine the evolution of the single-particle gap, quasiparticle residue of the doped hole at momentum $(\pi,\pi)$, and spin gap across the magnetic order-disorder transition. Our results indicate that increasing $N$ modifies the behavior of the coherence temperature: while it evolves smoothly across the magnetic transition at $N=2$ it develops an abrupt jump -- of up to an order of magnitude -- at larger but finite $N$. We discuss the magnetic order-disorder transition from a quantum-field-theoretic perspective and comment on implications of our findings for the interpretation of experiments on quantum critical heavy-fermion compounds.
- arXiv:1910.08610 (replaced) [pdf, other]
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Title: Probing quantum spin liquids in equilibrium using the inverse spin Hall effectComments: 17 pages, 6 figuresSubjects: Strongly Correlated Electrons (cond-mat.str-el)
We propose an experimental method utilizing a strongly spin-orbit coupled metal to quantum magnet bilayer that will probe quantum magnets lacking long range magnetic order, e.g., quantum spin liquids, via examination of the voltage noise spectrum in the metal layer. The bilayer is held in thermal and chemical equilibrium, and spin fluctuations arising across the single interface are converted into voltage fluctuations in the metal as a result of the inverse spin Hall effect. We elucidate the theoretical workings of the proposed bilayer system, and provide precise predictions for the frequency characteristics of the enhancement to the ac electrical resistance measured in the metal layer for three candidate quantum spin liquid models. Application to the Heisenberg spin-$1/2$ kagom{\'e} lattice model should allow for the extraction of any spinon gap present. A quantum spin liquid consisting of fermionic spinons coupled to a $U(1)$ gauge field should cause subdominant $\W^{4/3}$ scaling of the resistance of the coupled metal. Finally, if the magnet is well-captured by the Kitaev model in the gapless spin liquid phase, then the proposed bilayer can extract the two-flux gap which arises in spite of the gapless spectrum of the fermions. We therefore show that spectral analysis of the ac resistance in the metal in a single interface, equilibrium bilayer can test the relevance of a quantum spin liquid model to a given candidate material.
- arXiv:1911.03580 (replaced) [pdf, other]
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Title: Deep learning the Hohenberg-Kohn maps of Density Functional TheorySubjects: Disordered Systems and Neural Networks (cond-mat.dis-nn); Quantum Physics (quant-ph)
A striking consequence of the Hohenberg-Kohn theorem of density functional theory is the existence of a bijection between the local density and the ground-state many-body wave function. Here we study the problem of constructing approximations to the Hohenberg-Kohn map using a statistical learning approach. Using supervised deep learning with synthetic data, we show that this map can be accurately constructed for a chain of one-dimensional interacting spinless fermions, in different phases of this model including the charge ordered Mott insulator and metallic phases and the critical point separating them. However, we also find that the learning is less effective across quantum phase transitions, suggesting an intrinsic difficulty in efficiently learning non-smooth functional relations. We further study the problem of directly reconstructing complex observables from simple local density measurements, proposing a scheme amenable to statistical learning from experimental data.
- arXiv:1911.04188 (replaced) [pdf, other]
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Title: Unconventional pairing in one-dimensional systems of a few mass-imbalanced ultracold fermionsJournal-ref: Phys. Rev. A 101, 033603 (2020)Subjects: Quantum Gases (cond-mat.quant-gas); Superconductivity (cond-mat.supr-con); Quantum Physics (quant-ph)
We study the ground-state properties of a two-component fermionic mixture effectively confined in a one-dimensional harmonic trap. We consider scenarios when numbers of particles in components are the same but particles have different masses. We examine whether it is possible to detect signatures of an unconventional pairing between opposite-spin fermions in the presence of attractive interactions. For this purpose, we perform the exact diagonalization of the many-body Hamiltonian and study the two-particle reduced density matrix. In agreement with expectations, we confirm that the many-body ground state is dominated by conventional pairs with a negligible total momentum for a small mass imbalance. Furthermore, we show that for sufficiently large mass ratios the domination of fundamentally different pairs is established and the Fulde-Ferrell-Larkin-Ovchinnikov phase is supported. Finally, we argue that the two mechanisms can coexist in the regime of moderate mass ratios. Due to the current experimental progress in obtaining ultra-cold fermionic systems in a few-body regime, our predictions may have some importance for the upcoming experiments.
- arXiv:1911.05318 (replaced) [pdf, other]
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Title: Dynamical density response and collective modes of topological insulator ultra-thin filmsComments: 10 pages, 8 figuresJournal-ref: Phys. Rev. B 101, 115108 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We analytically calculate the intra- and inter-surface dynamical density-density linear responses of ultra-thin topological insulator films with finite tunneling between their top and bottom surfaces in both metallic and insulating regimes. Employing the random phase approximation we investigate the dispersions of in-phase and out-of-phase collective density modes of this system in the metallic regime. We find that in contrast to the bilayers of the conventional two-dimensional electron gas, where finite tunneling gaps out the out-of-phase mode, in topological insulator thin films, this mode remains linear at long wavelengths. Depending on different system parameters, the velocity of out-of-phase mode can be tuned to be larger or substantially smaller than the Fermi velocity of electrons on the isolated surfaces of the topological insulator. Finite tunneling generally reduces the energy of collective modes, making them more confined in space.
- arXiv:1911.05667 (replaced) [pdf, other]
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Title: Consequences of Time-reversal-symmetry Breaking in the Light-Matter Interaction: Berry Curvature, Quantum Metric and Diabatic MotionComments: 15+4 pages, 5 figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Nonlinear optical response is well studied in the context of semiconductors and has gained a renaissance in studies of topological materials in the recent decade. So far it mainly deals with non-magnetic materials and it is believed to root in the Berry curvature of the material band structure. In this work, we revisit the general formalism for the second-order optical response and focus on the consequences of the time-reversal-symmetry ($\mathcal{T}$) breaking, by a diagrammatic approach. We have identified three physical mechanisms to generate a dc photocurrent, i.e. the Berry curvature, the quantum metric, and the diabatic motion. All three effects can be understood intuitively from the anomalous acceleration. The first two terms are respectively the antisymmetric and symmetric parts of the quantum geometric tensor. The last term is due to the dynamical antilocalization that appears from the phase accumulation between time-reversed fermion loops. Additionally, we derive the semiclassical conductivity that includes both intra- and interband effects. We find that $\mathcal{T}$-breaking can lead to a greatly enhanced non-linear anomalous Hall effect that is beyond the contribution by the Berry curvature dipole.
- arXiv:1911.10347 (replaced) [pdf, other]
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Title: Evidence the ferromagnetic order on CoSb layer of LaCoSb$_2$Authors: Muyuan Zou, Jianan Chu, Hui Zhang, Tianzhong Yuan, Peng Cheng, Wentao Jin, Da Jiang, Xuguang Xu, Wenjie Yu, Zhenghua An, Xinyuan Wei, Gang Mu, Wei LiComments: 10 pages, 7 figures, 3 tableJournal-ref: Phys. Rev. B 101, 155138 (2020)Subjects: Superconductivity (cond-mat.supr-con); Strongly Correlated Electrons (cond-mat.str-el)
The emergence of unconventional superconductivity is generally considered to be related to spin fluctuations. Unveiling the intriguing behaviors of spin fluctuations in parent compounds with layered transition-metal ions may shed light on the search for exotic unconventional superconductors. Here, based on the framework of the first-principles calculations, we theoretically propose that LaCoSb$_2$ is a weak antiferromagnetic layered metal with an in-plane ferromagnetic moment of 0.88 $\mu_B$ at the Co sites, as a candidate parent compound of the cobalt-based superconductors. Importantly, this theoretical finding is experimentally supported by our magnetization measurements on polycrystalline samples of LaCo$_{0.78}$Sb$_2$. Following the symmetry analysis, we suggest a possible $p$-wave superconductivity hosted in doped LaCoSb$_2$ emerging at the verge of ferromagnetic spin fluctuations, which implies potential applications in topological quantum computing in future.
- arXiv:1912.01027 (replaced) [pdf, other]
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Title: Disentangling quantum matter with measurementsComments: 36 pages, 12 figures. v2: many improvements in presentationJournal-ref: Phys. Rev. B 101, 115131 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el); Statistical Mechanics (cond-mat.stat-mech); Quantum Physics (quant-ph)
Measurements destroy entanglement. Building on ideas used to study `quantum disentangled liquids', we explore the use of this effect to characterize states of matter. We focus on systems with multiple components, such as charge and spin in a Hubbard model, or local moments and conduction electrons in a Kondo lattice model. In such systems, measurements of (a subset of) one of the components can leave behind a quantum state of the other that is easy to understand, for example in terms of scaling of entanglement entropy of subregions. We bound the outcome of this protocol, for any choice of measurement, in terms of more standard information-theoretic quantities. We apply this quantum disentangling protocol to several problems of physical interest, including gapless topological phases, heavy fermions, and scar states in Hubbard model.
- arXiv:1912.02335 (replaced) [pdf, other]
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Title: Evidence for nanocoulomb charges on spider ballooning silkAuthors: Erica L. Morley (1), Peter W. Gorham (2), ((1) School of Biological Sciences, University of Bristol, (2) Dept. of Physics and Astronomy, University of Hawaii at Manoa)Comments: 12 pages, 7 figures, accepted for publication in Physical Review ESubjects: Biological Physics (physics.bio-ph); Soft Condensed Matter (cond-mat.soft)
We report on three launches of ballooning $Erigone$ spiders observed in a 0.9 m$^3$ laboratory chamber, controlled under conditions where no significant air motion was possible. These launches were elicited by vertical, downward-oriented electric fields within the chamber, and the motions indicate clearly that negative electric charge on the ballooning silk, subject to the Coulomb force, produced the lift observed in each launch. We estimate the total charge required under plausible assumptions, and find that at least 1.15 nC is necessary in each case. The charge is likely to be non-uniformly distributed, favoring initial longitudinal mobility of electrons along the fresh silk during extrusion. These results demonstrate for the first time that spiders are able to utilize charge on their silk to attain electrostatic flight even in the absence of any aerodynamic lift.
- arXiv:1912.03693 (replaced) [pdf, ps, other]
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Title: Magnetic excitations in magnetization plateaux of a frustrated spin ladderComments: 10 pages, 7 figuresJournal-ref: Phys. Rev. B 101, 144407 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el)
Magnetization plateaux emerging in quantum spin systems due to spontaneously breaking of translational symmetry have been reported both theoretically and experimentally. The broken symmetry can induce reconstruction of elementary excitations such as Goldstone and Higgs modes, whereas its microscopic mechanism and reconstructed quasi-particle in magnetization-plateau phases have remained unclear so far. Here we theoretically study magnetic excitations in the magnetization-plateau phases of a frustrated spin ladder by using dynamical density-matrix renormalization-group method. Additionally, analytical approaches with perturbation theory are performed to obtain intuitive view of magnetic excitations. Comparison between numerical and analytical results indicates the presence of a reconstructed quasi-particle originating from spontaneously broken translational symmetry, which is realized as a collective mode of spin trimer called trimeron.
- arXiv:1912.04267 (replaced) [pdf, other]
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Title: Non-adiabatic effects and exciton-like states during insulator-to-metal transition in warm dense hydrogenComments: 7 pages, 4 figures, Supplemental Material (10 pages)Journal-ref: Phys. Rev. B 101, 100101 (2020)Subjects: Materials Science (cond-mat.mtrl-sci)
Transition of molecular hydrogen to atomic ionized state with increase of temperature and pressure poses still unresolved problems for experimental methods and theory. Here we analyze the dynamics of this transition and show its nonequilibrium non-adiabatic character overlooked in both interpreting experimental data and in theoretical models. The non-adiabatic mechanism explains the strong isotopic effect [Zaghoo, Husband, and Silvera, Phys. Rev. B 98, 104102 (2018)] and the large latent heat [Houtput, Tempere, and Silvera, Phys. Rev. B 100, 134106 (2019)] reported recently. We demonstrate the possibility of formation of intermediate exciton-like molecular states at heating of molecular hydrogen that can explain puzzling experimental data on reflectivity and conductivity during the insulator-to-metal transition.
- arXiv:1912.09649 (replaced) [pdf, ps, other]
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Title: How to obtain complex transition dipole moments satisfying crystal symmetry and periodicity from ab-initio calculationsSubjects: Optics (physics.optics); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Transition dipole moments (TDM) between energy bands of solids deserve special attention nowadays as intense lasers can easily drive non-adiabatic transitions of excited electron wave packets across the Brillouin zones. The TDM is required to be continuous, satisfying crystal symmetry, and periodic at zone boundaries. While present day ab-initio algorithms are powerful in calculating band structures of solids, they all introduced random phases into the eigenfunctions at each crystal momentum k. In this paper, we show how to choose a ``smooth-periodic'' gauge where TDMs can be smooth versus k, preserving crystal symmetry, as well as maintaining periodic at zone boundaries. Based on band structure and TDMs in the ``smooth-periodic'' gauge calculated from ab-initio algorithms, we revisit high-order harmonic generation from MgO which exhibits inversion symmetry and ZnO which has broken symmetry. The symmetry properties of TDMs with respect to k ensure the absence of even-order harmonics in system with inversion symmetry, while the TDM in the `smooth-periodic'' gauge for ZnO is shown to enhance even harmonics that were underestimated in previous simulations. These results reveal the importance of correctly treating the complex TDMs in nonlinear laser-solid interactions which has been elusive so far.
- arXiv:1912.11650 (replaced) [pdf, ps, other]
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Title: Field-Orientation Effect on Ferro-Quadrupole Order in PrTi2Al20Authors: Shunichiro Kittaka, Takanori Taniguchi, Kazumasa Hattori, Shota Nakamura, Toshiro Sakakibara, Masashi Takigawa, Masaki Tsujimoto, Akito Sakai, Yosuke Matsumoto, Satoru NakatsujiComments: 5 pages, 5 figures (main text) + 4 pages, 2 figures (supplemental material), accepted for publication in J. Phys. Soc. JpnJournal-ref: J. Phys. Soc. Jpn. 89, 043701 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el)
Ferro-quadrupole (FQ) order in the non-Kramers $\Gamma_3$ doublet system PrTi$_2$Al$_{20}$ has been investigated via angle-resolved measurements of the specific heat, rotational magnetocaloric effect, and entropy, under a rotating magnetic field within the $(1\bar{1}0)$ plane. The FQ transition occurring at 2 K is robust when the magnetic field $B$ is applied precisely along the $[111]$ direction. By contrast, the magnetic field of larger than 1 T tilted away from the $[111]$ direction sensitively changes the FQ transition to a crossover. The energy gap between the ground and first-excited states in the FQ order increases remarkably with the magnetic field in $B \parallel [001]$, but hardly depends on the magnetic-field strength, at least up to 5 T, in the field orientation between the $[111]$ and $[110]$ axes. These features can be reproduced by using a phenomenological model for FQ order assuming an anisotropic field-dependent interaction between quadrupoles, which has been recently proposed to explain the field-induced first-order phase transition in PrTi$_2$Al$_{20}$. The present study demonstrates the great potential of the field-angle-resolved measurements for evaluating possible scenarios for multipole orders.
- arXiv:1912.12464 (replaced) [pdf, other]
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Title: Frustration-Induced Supersolid Phases of Extended Bose-Hubbard Model in the Hard-Core LimitComments: 13 pages, 10 figuresSubjects: Other Condensed Matter (cond-mat.other); Quantum Gases (cond-mat.quant-gas)
We investigate exotic supersolid phases in the extended Bose-Hubbard model with infinite projected entangled-pair state, numerical exact diagonalization, and mean-field theory. We demonstrate that many different supersolid phases can be generated by changing signs of hopping terms, and the interactions along with the frustration of hopping terms are important to stabilize those supersolid states. We argue the effect of frustration introduced by the competition of hopping terms in the supersolid phases from the mean-field point of view. This helps to give a clearer picture of the background mechanism for underlying superfluid/supersolid states to be formed. With this knowledge, we predict and realize the $d$-wave superfluid, which shares the same pairing symmetry with high-$T_c$ materials, and its extended phases. We believe that our results contribute to preliminary understanding for desired target phases in the real-world experimental systems.
- arXiv:1912.13293 (replaced) [pdf]
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Title: Unconventional superconductivity in highly-compressed unannealed sulphur hydrideAuthors: E.F. TalantsevComments: 8 pages, 2 figures, 1 tableJournal-ref: Results in Physics 16, 102993 (2020)Subjects: Superconductivity (cond-mat.supr-con)
While great scientific efforts focus on the synthesis and studies of near-room-temperature (NRT) superconductors exhibited record superconducting transition temperatures (for instance, laser annealed H3S, LaH10 and YHn (n = 4,6,7,9) with Tc > 200 K), unannealed low-Tc counterparts of NRT superconductors stay in the background. However, the formers are part of hydrogen-rich superconductors family and the success in understanding of NRT superconductivity depends on the study of these materials too. In this paper we analyse experimental temperature dependent upper critical field data, Bc2(T), reported by Drozdov et al (Nature 525, 73 (2015)) for unannealed highly-compressed (P = 155 GPa) sulphur hydride with Tc = 46 K and show that this material is unconventional superconductor which exhibits the ratio of Tc to the Fermi temperature, TF, in the range of 0.02 < Tc/TF < 0.05.
- arXiv:2001.00021 (replaced) [pdf, other]
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Title: Efficient classical simulation of random shallow 2D quantum circuitsAuthors: John Napp, Rolando L. La Placa, Alexander M. Dalzell, Fernando G. S. L. Brandao, Aram W. HarrowComments: 83 pages, 17 figures. v2: minor fixes and clarifications, added a referenceSubjects: Quantum Physics (quant-ph); Statistical Mechanics (cond-mat.stat-mech); Computational Complexity (cs.CC)
Random quantum circuits are commonly viewed as hard to simulate classically. In some regimes this has been formally conjectured, and there had been no evidence against the more general possibility that for circuits with uniformly random gates, approximate simulation of typical instances is almost as hard as exact simulation. We prove that this is not the case by exhibiting a shallow circuit family with uniformly random gates that cannot be efficiently classically simulated near-exactly under standard hardness assumptions, but can be simulated approximately for all but a superpolynomially small fraction of circuit instances in time linear in the number of qubits and gates. We furthermore conjecture that sufficiently shallow random circuits are efficiently simulable more generally. To this end, we propose and analyze two simulation algorithms. Implementing one of our algorithms numerically, we give strong evidence that it is efficient both asymptotically and, in some cases, in practice. To argue analytically for efficiency, we reduce the simulation of 2D shallow random circuits to the simulation of a form of 1D dynamics consisting of alternating rounds of random local unitaries and weak measurements -- a type of process that has generally been observed to undergo a phase transition from an efficient-to-simulate regime to an inefficient-to-simulate regime as measurement strength is varied. Using a mapping from quantum circuits to statistical mechanical models, we give evidence that a similar computational phase transition occurs for our algorithms as parameters of the circuit architecture like the local Hilbert space dimension and circuit depth are varied.
- arXiv:2001.01009 (replaced) [pdf, other]
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Title: Observation of the Interlayer Exciton Gases in WSe$_2$ -pWSe$_2$ HeterostructuresAuthors: Zheng Sun, Jonathan Beaumariage, Qingrui Cao, Kenji Watanabe, Takashi Taniguchi, Benjamin Hunt, David W SnokeSubjects: Materials Science (cond-mat.mtrl-sci); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Interlayer excitons (IXs) possess a much longer lifetime than intralayer excitons due to the spatial separation of the electrons and holes; hence, they have been pursued to create exciton condensates for decades. The recent emergence of two-dimensional (2D) materials, such as transition metal dichalcogenides (TMDs), and of their van der Waals heterostructures (HSs), in which two different 2D materials are layered together, has created new opportunities to study IXs. Here we present the observation of IX gases within two stacked structures consisting of hBN/WSe$_2$/hBN/p: WSe$_2$/hBN. The IX energy of the two different structures differed by 82 meV due to the different thickness of the hBN spacer layer between the TMD layers. We demonstrate that the lifetime of the IXs is shortened when the temperature decreases or when the pump power increases. We attribute this nonlinear behavior to an Auger process.
- arXiv:2001.01616 (replaced) [pdf, other]
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Title: A new self-consistent approach of quantum turbulence in superfluid heliumComments: 19 pages, 9 figuresSubjects: Fluid Dynamics (physics.flu-dyn); Quantum Gases (cond-mat.quant-gas)
We present the Fully cOUpled loCAl model of sUperfLuid Turbulence (FOUCAULT) that describes the dynamics of finite temperature superfluids. The superfluid component is described by the vortex filament method while the normal fluid is governed by a modified Navier-Stokes equation. The superfluid vortex lines and normal fluid components are fully coupled in a self-consistent manner by the friction force, which induces local disturbances in the normal fluid in the vicinity of vortex lines. The main focus of this work is the numerical scheme for distributing the friction force to the mesh points where the normal fluid is defined and for evaluating the velocity of the normalfluid on the Lagrangian discretization points along the vortex lines. In particular, we show that if this numerical scheme is not careful enough, spurious results may occur. The new scheme which we propose to overcome these difficulties is based on physical principles. Finally, we apply the new method to the problem of the motion of a superfluid vortex ring in a stationary normal fluid and in a turbulent normal fluid.
- arXiv:2001.01693 (replaced) [pdf, ps, other]
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Title: Susceptibility of the one-dimensional Ising model: is the singularity at T = 0 an essential one?Authors: James H. TaylorComments: 8 pagesSubjects: Statistical Mechanics (cond-mat.stat-mech)
The zero-field, isothermal susceptibility of the classical one-dimensional Ising model is shown to have a relatively simple singularity as the temperature approaches zero, proportional only to the inverse temperature. This is in contrast to what is seen throughout the literature: an essential singularity involving an exponential dependence on the inverse temperature. The analysis involves nothing beyond straightforward series expansions, starting either with the partition function for a closed chain in a magnetic field, obtained using the transfer matrix approach; or from the expression for the zero-field susceptibility found via the fluctuation-dissipation theorem. In both cases, the exponential singularity is cancelled by part of a term that is usually considered ignorable in the thermodynamic limit.
- arXiv:2001.02742 (replaced) [pdf, other]
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Title: Self-Consistent Quantum-Field Theory for the Characterization of Complex Random Media by Short Laser PulsesComments: published 13 pages, 7 figuresJournal-ref: Phys. Rev. Research 2, 013324 (2020)Subjects: Disordered Systems and Neural Networks (cond-mat.dis-nn); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Soft Condensed Matter (cond-mat.soft); Computational Physics (physics.comp-ph); Optics (physics.optics)
We present a quantum field theoretical method for the characterization of disordered complex media with short laser pulses in an optical coherence tomography setup (OCT). We solve this scheme of coherent transport in space and time with weighted essentially nonoscillatory methods (WENO). WENO is preferentially used for the determination of highly nonlinear and discontinuous processes including interference effects and phase transitions like Anderson localization of light. The theory determines spatiotemporal characteristics of the scattering mean free path and the transmission cross section that are directly measurable in time-of-flight (ToF) and pump-probe experiments. The results are a measure of the coherence of multiple scattering photons in passive as well as in optically soft random media. Our theoretical results of ToF are instructive in spectral regions where material characteristics such as the scattering mean free path and the diffusion coefficient are methodologically almost insensitive to gain or absorption and to higher-order nonlinear effects. Our method is applicable to OCT and other advanced spectroscopy setups including samples of strongly scattering mono- and polydisperse complex nano- and microresonators.
- arXiv:2001.03079 (replaced) [pdf, ps, other]
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Title: Stationary Gaussian Free Fields Coupled with Stochastic Log-Gases via Multiple SLEsComments: v3: LaTeX 20 pages, no figureSubjects: Probability (math.PR); Statistical Mechanics (cond-mat.stat-mech); Mathematical Physics (math-ph)
Miller and Sheffield introduced a notion of an imaginary surface as an equivalence class of pairs of simply connected proper subdomains of $\mathbb{C}$ and Gaussian free fields (GFFs) on them under conformal equivalence. They considered the situation in which the conformal transformations are given by a chordal Schramm--Loewner evolution (SLE). In the present paper, we construct processes of GFF on $\mathbb{H}$ (the upper half-plane) and $\mathbb{O}$ (the first orthant of $\mathbb{C}$) by coupling zero-boundary GFFs on these domains with stochastic log-gases defined on parts of boundaries of the domains, $\mathbb{R}$ and $\mathbb{R}_+$, called the Dyson model and the Bru--Wishart process, respectively, using multiple SLEs evolving in time. We prove that the obtained processes of GFF are stationary. The stationarity defines an equivalence relation between GFFs, and the pairs of time-evolutionary domains and stationary processes of GFF will be regarded as generalizations of the imaginary surfaces studied by Miller and Sheffield.
- arXiv:2001.03347 (replaced) [pdf, other]
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Title: Emergence of quasiparticle multiplets in curiumComments: 7 pages, 4 figuresJournal-ref: Phys. Rev. B 101, 195123 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el); Materials Science (cond-mat.mtrl-sci)
A combination of the density functional theory and the single-site dynamical mean-field theory is employed to study the electronic structures of various allotropes of elemental curium (Cm-I, Cm-II, and Cm-III). We find that the 5$f$ valence electrons in the high-symmetry Cm-I and Cm-II phases remain localized, while they turn into itinerancy in the low-symmetry monoclinic Cm-III phase. In addition, conspicuous quasiparticle multiplets are identified in the 5$f$ electronic density of states of the Cm-III phase. We believe that it is the many-body transition between $5f^{7}$ and $5f^{8}$ configurations that gives rise to these quasiparticle multiplets. Therefore, the Cm-III phase is probably a new realization of the so-called Racah metal.
- arXiv:2001.03475 (replaced) [pdf, other]
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Title: Majorana bound states in quantum spin Hall slitsSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Superconductivity (cond-mat.supr-con)
We propose a novel realization for a topologically superconducting phase hosting Majorana zero-modes on the basis of quantum spin Hall systems. Remarkably, our proposal is completely free of ferromagnets. Instead, we confine helical edge states around a narrow defect line of finite length in a two-dimensional topological insulator. We demonstrate the formation of a new topological regime, hosting protected Majorana modes in the presence of s-wave superconductivity and Zeeman coupling. Interestingly, when the system is weakly tunnel-coupled to helical edge state reservoirs, a truly unambiguous transport signature is associated with the presence of a non-Abelian Majorana zero-mode.
- arXiv:2001.05143 (replaced) [pdf, ps, other]
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Title: Doping and temperature evolution of pseudogap and spin-spin correlations in the two-dimensional Hubbard modelComments: 12 pages, 17 figuresJournal-ref: Phys. Rev. B 101, 115141 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el)
Cluster perturbation theory is applied to the two-dimensional Hubbard $t-t'-t''-U$ model to obtain doping and temperature dependent electronic spectral function with $4 \times 4$ and 12-site clusters. It is shown that evolution of the pseudogap and electronic dispersion with doping and temperature is similar and in both cases it is significantly influenced by spin-spin short-range correlations. When short-range magnetic order is weakened by doping or temperature and Hubbard-I like electronic dispersion becomes more pronounced, the Fermi arc turns into large Fermi surface and the pseudogap closes. It is demonstrated how static spin correlations impact the overall dispersion's shape and how accounting for dynamic contributions leads to momentum-dependent spectral weight at the Fermi surface and broadening effects.
- arXiv:2001.05972 (replaced) [pdf, other]
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Title: Topological Descriptors Help Predict Guest Adsorption in Nanoporous MaterialsComments: 14 pages, 7 figuresSubjects: Materials Science (cond-mat.mtrl-sci); Machine Learning (cs.LG); Algebraic Topology (math.AT); Computational Physics (physics.comp-ph)
Machine learning has emerged as an attractive alternative to experiments and simulations for predicting material properties. Usually, such an approach relies on specific domain knowledge for feature design: each learning target requires careful selection of features that an expert recognizes as important for the specific task. The major drawback of this approach is that computation of only a few structural features has been implemented so far, and it is difficult to tell a priori which features are important for a particular application. The latter problem has been empirically observed for predictors of guest uptake in nanoporous materials: local and global porosity features become dominant descriptors at low and high pressures, respectively. We investigate a feature representation of materials using tools from topological data analysis. Specifically, we use persistent homology to describe the geometry of nanoporous materials at various scales. We combine our topological descriptor with traditional structural features and investigate the relative importance of each to the prediction tasks. We demonstrate an application of this feature representation by predicting methane adsorption in zeolites, for pressures in the range of 1-200 bar. Our results not only show a considerable improvement compared to the baseline, but they also highlight that topological features capture information complementary to the structural features: this is especially important for the adsorption at low pressure, a task particularly difficult for the traditional features. Furthermore, by investigation of the importance of individual topological features in the adsorption model, we are able to pinpoint the location of the pores that correlate best to adsorption at different pressure, contributing to our atom-level understanding of structure-property relationships.
- arXiv:2001.06008 (replaced) [pdf, other]
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Title: Green's function methods for single molecule junctionsComments: Perspective. 25 pages, 8 figuresJournal-ref: J. Chem. Phys. 152, 090901 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Strongly Correlated Electrons (cond-mat.str-el); Chemical Physics (physics.chem-ph)
We present a brief pedagogical review of theoretical Green's function methods applicable to open quantum systems out of equilibrium in general, and single molecule junctions in particular. We briefly describe experimental advances in molecular electronics, then discuss different theoretical approaches. We then focus on Green's function methods. Two characteristic energy scales governing the physics are many-body interactions within the junctions, and molecule-contact coupling. We therefore discuss weak interactions and weak coupling, as two limits that can be conveniently treated within, respectively, the standard nonequilibrium Green's function (NEGF) method and its many-body flavors (pseudoparticle and Hubbard NEGF). We argue that the intermediate regime, where the two energy scales are comparable, can in many cases be efficiently treated within the recently introduced superperturbation dual fermion approach. Finally, we review approaches for going beyond these analytically accessible limits, as embodied by recent developments in numerically exact methods based on Green's functions.
- arXiv:2001.08019 (replaced) [pdf, ps, other]
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Title: Spontaneous motion of a camphor particle with a three-mode modification from a circleComments: 12 pages, 3 figuresSubjects: Pattern Formation and Solitons (nlin.PS); Soft Condensed Matter (cond-mat.soft)
The spontaneous motion of a camphor particle with a slight modification from a circle is investigated. The effect of the shape on the motion is discussed using the perturbation method. The results predict that a camphor particle with a three-mode modification from a circle moves in the direction of a corner for the smaller particle, while it moves in the direction of a side for the larger particle. The numerical simulation results well reproduce the theoretical prediction. The present study will help the understanding on the effect of the particle shape on the spontaneous motion.
- arXiv:2001.11706 (replaced) [pdf, other]
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Title: Noninteracting trapped Fermions in double-well potentials: inverted parabola kernelComments: 16 pages, 8 figuresJournal-ref: Phys. Rev. A 101, 053602 (2020)Subjects: Statistical Mechanics (cond-mat.stat-mech); Quantum Gases (cond-mat.quant-gas); Mathematical Physics (math-ph)
We study a system of $N$ noninteracting spinless fermions in a confining, double-well potential in one dimension. When the Fermi energy is close to the value of the potential at its local maximum we show that physical properties, such as the average density and the fermion position correlation functions, display a universal behavior that depends only on the local properties of the potential near its maximum. This behavior describes the merging of two Fermi gases, which are disjoint at sufficiently low Fermi energies. We describe this behavior in terms of a new correlation kernel that we compute analytically and we call it the inverted parabola kernel". As an application, we calculate the mean and variance of the number of particles in an interval of size $2L$ centered around the position of the local maximum, for sufficiently small $L$. Finally, we discuss the possibility of observing our results in experiments, as well as the extensions to nonzero temperature and to higher space dimensions.
- arXiv:2002.02979 (replaced) [pdf, other]
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Title: Localization transition on the Random Regular Graph as an unstable tricritical point in a log-normal Rosenzweig-Porter random matrix ensembleComments: 11 pages, 9 figures, 2 tables, 48 references + 8 pages, 6 figures in AppendicesSubjects: Disordered Systems and Neural Networks (cond-mat.dis-nn); Quantum Gases (cond-mat.quant-gas)
Gaussian Rosenzweig-Porter (GRP) random matrix ensemble is the only one in which the robust multifractal phase and ergodic transition have a status of a mathematical theorem. Yet, this phase in GRP model is oversimplified: the spectrum of fractal dimensions is degenerate and the mini-band in the local spectrum is not multifractal. In this paper we suggest an extension of the GRP model by adopting a logarithmically-normal (LN) distribution of off-diagonal matrix elements. A family of such LN-RP models is parametrized by a symmetry parameter $p$ and it interpolates between the GRP at $p\rightarrow 0$ and Levy ensembles at $p\rightarrow\infty$. A special point $p=1$ is shown to be the simplest approximation to the Anderson localization model on a random regular graph.We study in detail the phase diagram of LN-RP model and show that $p=1$ is a tricritical point where the multifractal phase first collapses. This collapse is shown to be unstable with respect to the truncation of the log-normal distribution. We suggest a new criteria of stability of the non-ergodic phases and prove that the Anderson transition in LN-RP model is discontinuous at all $p>0$.
- arXiv:2002.06574 (replaced) [pdf, ps, other]
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Title: Wave scattering in frequency domainAuthors: Tatsuya UsukiComments: 55 pages, 8 figures, v3 revised typos in ch.4, v2 revised eq.3.7Subjects: Computational Physics (physics.comp-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Optics (physics.optics)
This report shows formulation of wave scattering in frequency domain. The formulation provides an understanding of S-matrix solver which is named as Scattering Matrix Analyzer (SMatrAn).
The S-matrix has the whole of amplitude and phase information for reflected and transmitted waves from a complicated scatterer. Accurate S-matrix leads to quantitative evaluation of scattering wave.
We can understand all formulas for the SMatrAn after reading this report. The S-matrix provided by SMatrAn will give us detailed analysis on complicated scattering in optical structure. - arXiv:2002.07329 (replaced) [pdf]
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Title: Stick-slip Avalanches in Steady Shearing: Signature of Transition between Granular Fluid and SolidSubjects: Soft Condensed Matter (cond-mat.soft); Fluid Dynamics (physics.flu-dyn)
By observing the fluctuations of fluid-immersed granular particles upon steady shearing, we identify a transitional zone that sets the system apart from fluidic sliding and signals the onset of solid mechanics, as the shear rate decreases. Toward the slow extreme, statistical analyses of the avalanche events combined with internal imaging capture the continuous yet distinctive change of behaviors, and offer test grounds for theories on the development of plasticity. We link such transition with the velocity weakening of inter-particle frictions, and propose a three-state phase diagram that bridges our discoveries on tightly packed granular systems and previous understanding of suspension rheology.
- arXiv:2002.08940 (replaced) [pdf, other]
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Title: Phonon Transport in Patterned Two-Dimensional Materials from First PrinciplesAuthors: Giuseppe RomanoSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci)
Phonon size effects induce ballistic transport in nanomaterials, challenging Fourier's law. Nondiffusive heat transport is captured by the Peierls-Boltzmann transport equation (BTE), commonly solved under the relaxation time approximation (RTA), which assumes diagonal scattering operator. Although the RTA is accurate for many relevant materials over a wide range of temperatures, such as silicon, it underpredicts thermal transport in most two-dimensional (2D) systems, notoriously graphene. Here we present a formalism, based on the BTE with the full collision matrix, for computing the effective thermal conductivity of arbitrarily patterned 2D materials. We apply our approach to porous graphene and find strong heat transport suppression in configurations with feature sizes of the order of micrometers; this result, which is rooted in the large generalized phonon MFPs in graphene, corroborates the possibility of strong thermal transport tunability by relatively coarse patterning. Lastly, we present a promising material configuration with low thermal conductivity. Our method enables the parameter-free design of 2D materials for thermoelectric and thermal routing applications.
- arXiv:2002.11176 (replaced) [pdf, other]
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Title: An elementary proof of 1D LSM theoremsAuthors: Abhishodh PrakashComments: 13 pages, 12 figures. Note added in Sec VII about important previous work that was brought to my attention after the appearance of this draft on arXiv, which had explored key aspects of this workSubjects: Strongly Correlated Electrons (cond-mat.str-el); High Energy Physics - Theory (hep-th)
The Lieb-Schultz-Mattis (LSM) theorem and its generalizations forbids the existence of a unique gapped ground state in the presence of certain lattice and internal symmetries and thus imposes powerful constraints on the low energy properties of quantum many-body systems. We provide an elementary proof of a class of generalized LSM theorems in 1D using matrix product state representations and the representation theory of groups.
- arXiv:2002.11924 (replaced) [pdf, other]
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Title: Path Integral for Spin-1 Chain in the Fluctuating Matrix Product State BasisComments: 4 pages, 1 figure, supplementary file included; references updatedSubjects: Strongly Correlated Electrons (cond-mat.str-el)
A new method of writing down the path integral for spin-1 Heisenberg antiferromagnetic chain is introduced. In place of the conventional coherent state basis that leads to the non-linear sigma-model, we use a new basis called the fluctuating matrix product states (fMPS) which embodies inter-site entanglement from the outset. It forms an overcomplete set spanning the entire Hilbert space of the spin-1 chain. Saddle-point analysis performed for the bilinear-biquadratic spin model predicts Affeck-Kennedy-Lieb-Tasaki (AKLT) state as the ground state in the vicinity of the AKLT Hamiltonian. Quadratic effective action derived by gradient expansion around the saddle point is free from constraints that plagued the non-linear sigma model and exactly solvable. The obtained excitation modes agree precisely with the single-mode approximation result for the AKLT Hamiltonian. Excitation spectra for other BLBQ Hamiltonians are obtained as well by diagonalizing the quadratic action.
- arXiv:2003.00793 (replaced) [pdf, other]
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Title: Quantum Many-Body Theory for Exciton-Polaritons in Semiconductor Mie Resonators in the Non-EquilibriumComments: published March 06, 2020Journal-ref: Appl. Sci. 10(5), 1836 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci); Optics (physics.optics); Quantum Physics (quant-ph)
We implement externally excited ZnO Mie resonators in a framework of a generalized Hubbard Hamiltonian to investigate the lifetimes of excitons and exciton-polaritons out of thermodynamical equilibrium. Our results are derived by a Floquet-Keldysh-Green's formalism with Dynamical Mean Field Theory (DMFT) and a second order iterative perturbation theory solver (IPT). We find that the Fano resonance which originates from coupling of the continuum of electronic density of states to the semiconductor Mie resonator yields polaritons with lifetimes between 0.6 ps and 1.45 ps. These results are compared to ZnO polariton lasers and to ZnO random lasers. We interpret the peaks of the exciton-polariton lifetimes in our results as a sign of gain narrowing which may lead to stable polariton lasing modes in the single excited ZnO Mie resonator. This form of gain may lead to polariton random lasing in an ensemble of ZnO Mie resonators in the non-equilibrium.
- arXiv:2003.01264 (replaced) [pdf, ps, other]
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Title: Quantal-classical fluctuation relation and the second law of thermodynamics: The quantum linear oscillatorAuthors: Ilki KimComments: 37 pages, 8 figuresSubjects: Statistical Mechanics (cond-mat.stat-mech); Quantum Physics (quant-ph)
In this work, we study the fluctuation relation and the second law of thermodynamics within a quantum linear oscillator externally driven over the period of time t = tau. To go beyond the standard approach (the two-point projective measurement one) to this subject and also render it discussed in both quantum and classical domains on the single footing, we recast this standard approach in terms of the Wigner function and its propagator in the phase space (x,p). With the help of the canonical transformation from (x,p) to the angle-action coordinates (\phi,I), we can then derive a measurement-free (classical-like) form of the Crooks fluctuation relation in the Wigner representation. This enables us to introduce the work W_{I_0,I_{tau}} associated with a single run from (I_0) to (I_{tau}) over the period tau, which is a quantum generalization of the thermodynamic work with its roots in the classical thermodynamics. This quantum work differs from the energy difference e_{I_0,I_{tau}} = e(I_{tau}) - e(I_0) unless beta, hbar --> 0. Consequently, we will obtain the quantum second-law inequality Delta F_{beta} \leq <W>_{P} \leq <e>_{P} = Delta U, where P, Delta F_{beta}, and <W>_P denote the work (quasi)-probability distribution, the free energy difference, and the average work distinguished from the internal energy difference Delta U, respectively, while <W>_P --> Delta U in the limit of beta, hbar --> 0 only. Therefore, we can also introduce the quantum heat Q_q = Delta U - W even for a thermally isolated system, resulting from the quantum fluctuation therein. This is a more fine-grained result than <W>_P = Delta U obtained from the standard approach. Owing to the measurement-free nature of the thermodynamic work W_{I_0,I_{tau}}, our result can also apply to the (non-thermal) initial states rho_0 = (1-gamma) rho_{beta} + gamma sigma with sigma \ne rho_{beta}.
- arXiv:2003.02408 (replaced) [pdf, other]
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Title: Thermodynamics of a deeply degenerate SU($N$)-symmetric Fermi gasAuthors: Lindsay Sonderhouse, Christian Sanner, Ross B. Hutson, Akihisa Goban, Thomas Bilitewski, Lingfeng Yan, William R. Milner, Ana Maria Rey, Jun YeComments: 10 pages, 5 figuresSubjects: Quantum Gases (cond-mat.quant-gas); Atomic Physics (physics.atom-ph)
Many-body quantum systems can exhibit a striking degree of symmetry unparalleled by their classical counterparts. While in real materials SU($N$) symmetry is an idealization, this symmetry is pristinely realized in fully controllable ultracold alkaline-earth atomic gases. Here, we study an SU($N$)-symmetric Fermi liquid of $^{87}$Sr atoms, where $N$ can be tuned to be as large as 10. In the deeply degenerate regime, we show through precise measurements of density fluctuations and expansion dynamics that the large $N$ of spin states under SU($N$) symmetry leads to pronounced interaction effects in a system with a nominally negligible interaction parameter. Accounting for these effects we demonstrate thermometry accurate to one-hundredth of the Fermi energy. We also demonstrate record speed for preparing degenerate Fermi seas, reaching $T/T_F = 0.12$ in under 3 s, enabled by the SU($N$) symmetric interactions. This, along with the introduction of a new spin polarizing method, enables operation of a 3D optical lattice clock in the band insulating-regime.
- arXiv:2003.02520 (replaced) [pdf, other]
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Title: Theory for the charge-density-wave mechanism of 3D quantum Hall effectComments: 6 pages, 4 figures, references and figures updatedSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Strongly Correlated Electrons (cond-mat.str-el)
The charge-density-wave (CDW) mechanism of the 3D quantum Hall effect has been observed recently in ZrTe$_5$ [Tang et al., Nature 569, 537 (2019)]. Quite different from previous cases, the CDW forms on a 1D band of Landau levels, which strongly depends on the magnetic field. However, its theory is still lacking. We develop a theory for the CDW mechanism of 3D quantum Hall effect. The theory can capture the main features in the experiments. We find a magnetic field induced second-order phase transition to the CDW phase. We find that electron-phonon interactions, rather than electron-electron interactions, dominate the order parameter. We extract the value of electron-phonon coupling constant from the non-Ohmic I-V relation. We point out a commensurate-incommensurate CDW crossover in the experiment. More importantly, our theory explores a rare case, in which a magnetic field can induce an order-parameter phase transition in one direction but a topological phase transition in other two directions, both depend on one magnetic field. It will be useful and inspire further experiments and theories on this emergent phase of matter.
- arXiv:2003.03334 (replaced) [pdf, other]
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Title: Finite-temperature transport in one-dimensional quantum lattice modelsComments: Review article (74 pages, 34 figures). Comments welcome. Version 2: Additional references, minor text modifications in Secs. I, III, IV, VISubjects: Strongly Correlated Electrons (cond-mat.str-el); Statistical Mechanics (cond-mat.stat-mech); Quantum Physics (quant-ph)
The last decade has witnessed an impressive progress in the theoretical understanding of transport properties of clean, one-dimensional quantum lattice systems. Many physically relevant models in one dimension are Bethe-ansatz integrable, including the anisotropic spin-1/2 Heisenberg (also called spin-1/2 XXZ chain) and the Fermi-Hubbard model. Nevertheless, practical computations of, for instance, correlation functions and transport coefficients pose hard problems from both the conceptual and technical point of view. Only due to recent progress in the theory of integrable systems on the one hand and due to the development of numerical methods on the other hand has it become possible to compute their finite temperature and nonequilibrium transport properties quantitatively. Most importantly, due to the discovery of a novel class of quasilocal conserved quantities, there is now a qualitative understanding of the origin of ballistic finite-temperature transport, and even diffusive or super-diffusive subleading corrections, in integrable lattice models. We shall review the current understanding of transport in one-dimensional lattice models, in particular, in the paradigmatic example of the spin-1/2 XXZ and Fermi-Hubbard models, and we elaborate on state-of-the-art theoretical methods, including both analytical and computational approaches. Among other novel techniques, we discuss matrix-product-states based simulation methods, dynamical typicality, and, in particular, generalized hydrodynamics. We will discuss the close and fruitful connection between theoretical models and recent experiments, with examples from both the realm of quantum magnets and ultracold quantum gases in optical lattices.
- arXiv:1204.2240 (replaced) [pdf, ps, other]
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Title: Interdependent binary choices under social influence: phase diagram for homogeneous unbiased populationsComments: 17 pages, 3 figures. This is the pre-peer reviewed version of the following article: Ana Fern\'andez del R\'io, Elka Korutcheva and Javier de la Rubia, Interdependent binary choices under social influence, Wiley's Complexity, 2012; which has been published in final form at this http URLJournal-ref: Complexity, Wiley, 2012Subjects: Physics and Society (physics.soc-ph); Statistical Mechanics (cond-mat.stat-mech); Social and Information Networks (cs.SI)
Coupled Ising models are studied in a discrete choice theory framework, where they can be understood to represent interdependent choice making processes for homogeneous populations under social influence. Two different coupling schemes are considered. The nonlocal or group interdependence model is used to study two interrelated groups making the same binary choice. The local or individual interdependence model represents a single group where agents make two binary choices which depend on each other. For both models, phase diagrams, and their implications in socioeconomic contexts, are described and compared in the absence of private deterministic utilities (zero opinion fields).
- arXiv:1603.05558 (replaced) [pdf]
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Title: Observation of charge density wave order in 1D mirror twin boundaries of single-layer MoSe2Authors: Sara Barja, Sebastian Wickenburg, Zhen-Fei Liu, Yi Zhang, Hyejin Ryu, Miguel M. Ugeda, Zahid Hussain, Z.-X. Shen, Sung-Kwan Mo, Ed Wong, Miquel B. Salmeron, Feng Wang, Michael F. Crommie, D. Frank Ogletree, Jeffrey B. Neaton, Alexander Weber-BargioniJournal-ref: Nature Phys 12, 751-756 (2016)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Properties of two-dimensional transition metal dichalcogenides are highly sensitive to the presence of defects in the crystal structure. A detailed understanding of defect structure may lead to control of material properties through defect engineering. Here we provide direct evidence for the existence of isolated, one-dimensional charge density waves at mirror twin boundaries in single-layer MoSe2. Our low-temperature scanning tunneling microscopy/spectroscopy measurements reveal a substantial bandgap of 60 - 140 meV opening at the Fermi level in the otherwise one dimensional metallic structure. We find an energy-dependent periodic modulation in the density of states along the mirror twin boundary, with a wavelength of approximately three lattice constants. The modulations in the density of states above and below the Fermi level are spatially out of phase, consistent with charge density wave order. In addition to the electronic characterization, we determine the atomic structure and bonding configuration of the one-dimensional mirror twin boundary by means of high-resolution non-contact atomic force microscopy. Density functional theory calculations reproduce both the gap opening and the modulations of the density of states.
- arXiv:1703.04532 (replaced) [pdf]
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Title: Standardization of Proton Induced X-Ray Emission for Analysis of Trace Elements in Thick TargetsComments: 6 PagesJournal-ref: Canadian Journal of Physics, 2019, 97:875-879Subjects: Instrumentation and Detectors (physics.ins-det); Materials Science (cond-mat.mtrl-sci)
This paper presents the standardization of Proton Induced X-rays Emission (PIXE) technique for the trace element analysis of thick standard samples. Three standard reference materials (SRMs) viz-\`a-vis titanium, copper and iron base alloys were used for the study due to their availability. The protons beam was accelerated up to 2.57 MeV energy by 5UDH-II tandem Pelletron accelerator and samples were irradiated at different geometry and durations. Spectrum was acquired using a multi-channel spectrum analyzer while spectrum analysis was done using a GUPIXWIN model for determination of elemental concentrations of trace elements. The obtained experimental data was compared with theoretical data and results were found in close agreement.
- arXiv:1712.08775 (replaced) [pdf, other]
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Title: Note on Green Function Formalism and Topological InvariantsComments: 19 pages, 3 figuresJournal-ref: J. Stat. Mech. (2020) 033101Subjects: High Energy Physics - Theory (hep-th); Strongly Correlated Electrons (cond-mat.str-el); Mathematical Physics (math-ph); Algebraic Topology (math.AT)
It has been discovered previously that the topological order parameter could be identified from the topological data of the Green's function, namely the (generalized) TKNN invariant in general dimensions, for both non-interacting and interacting systems. In this note, we show that this phenomenon has a clear geometric derivation. This proposal could be regarded as an alternative proof for the identification of the corresponding topological invariant and the topological order parameter.
- arXiv:1807.03334 (replaced) [pdf, other]
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Title: An introduction to the SYK modelAuthors: Vladimir RosenhausComments: 20 pagesJournal-ref: J. Phys. A: Math. Theor. 52 (2019) 323001Subjects: High Energy Physics - Theory (hep-th); Strongly Correlated Electrons (cond-mat.str-el); General Relativity and Quantum Cosmology (gr-qc); Mathematical Physics (math-ph); Quantum Physics (quant-ph)
These notes are a short introduction to the Sachdev-Ye-Kitaev model. We discuss: SYK and tensor models as a new class of large N quantum field theories, the near-conformal invariance in the infrared, the computation of correlation functions, generalizations of SYK, and applications to AdS/CFT and strange metals.
- arXiv:1809.11121 (replaced) [pdf, other]
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Title: Is there a Floquet Lindbladian?Journal-ref: Phys. Rev. B 101, 100301 (2020)Subjects: Quantum Physics (quant-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Quantum Gases (cond-mat.quant-gas); Statistical Mechanics (cond-mat.stat-mech)
The stroboscopic evolution of a time-periodically driven isolated quantum system can always be described by an effective time-independent Hamiltonian. Whether this concept can be generalized to open Floquet systems, described by a Markovian master equation with time-periodic Lindbladian generator, remains an open question. By using a two level system as a model, we explicitly show the existence of two well-defined parameter regions. In one region the stroboscopic evolution can be described by a Markovian master equation with a time-independent Floquet Lindbladian. In the other it cannot; but here the one-cycle evolution operator can be reproduced with an effective non-Markovian master equation that is homogeneous but non-local in time. Interestingly, we find that the boundary between the phases depends on when the evolution is stroboscopically monitored. This reveals the non-trivial role played by the micromotion in the dynamics of open Floquet systems.
- arXiv:1810.03364 (replaced) [pdf]
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Title: Identifying substitutional oxygen as a prolific point defect in monolayer transition metal dichalcogenides with experiment and theoryAuthors: Sara Barja, Sivan Refaely-Abramson, Bruno Schuler, Diana Y. Qiu, Artem Pulkin, Sebastian Wickenburg, Hyejin Ryu, Miguel M. Ugeda, Christoph Kastl, Christopher Chen, Choongyu Hwang, Adam Schwartzberg, Shaul Aloni, Sung-Kwan Mo, D. Frank Ogletree, Michael F. Crommie, Oleg V. Yazyev, Steven G. Louie, Jeffrey B. Neaton, Alexander Weber-BargioniJournal-ref: Nat Commun 10, 3382 (2019)Subjects: Materials Science (cond-mat.mtrl-sci)
Chalcogen vacancies are considered to be the most abundant point defects in two-dimensional (2D) transition-metal dichalcogenide (TMD) semiconductors, and predicted to result in deep in-gap states (IGS). As a result, important features in the optical response of 2D-TMDs have typically been attributed to chalcogen vacancies, with indirect support from Transmission Electron Microscopy (TEM) and Scanning Tunneling Microscopy (STM) images. However, TEM imaging measurements do not provide direct access to the electronic structure of individual defects; and while Scanning Tunneling Spectroscopy (STS) is a direct probe of local electronic structure, the interpretation of the chemical nature of atomically-resolved STM images of point defects in 2D-TMDs can be ambiguous. As a result, the assignment of point defects as vacancies or substitutional atoms of different kinds in 2D-TMDs, and their influence on their electronic properties, has been inconsistent and lacks consensus. Here, we combine low-temperature non-contact atomic force microscopy (nc-AFM), STS, and state-of-the-art ab initio density functional theory (DFT) and GW calculations to determine both the structure and electronic properties of the most abundant individual chalcogen-site defects common to 2D-TMDs. Surprisingly, we observe no IGS for any of the chalcogen defects probed. Our results and analysis strongly suggest that the common chalcogen defects in our 2D-TMDs, prepared and measured in standard environments, are substitutional oxygen rather than vacancies.
- arXiv:1810.13419 (replaced) [pdf, other]
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Title: Imaging emergent heavy Dirac fermions of a topological Kondo insulatorAuthors: Harris Pirie, Yu Liu, A. Soumyanarayanan, Pengcheng Chen, Yang He, M.M. Yee, P.F.S. Rosa, J.D. Thompson, Dae-Jeong Kim, Z. Fisk, Xiangfeng Wang, J. Paglione, Dirk K. Morr, M. H. Hamidian, Jennifer E. HoffmanJournal-ref: Nat. Phys. 16, 52 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el)
Kondo insulators are primary candidates in the search for strongly correlated topological quantum phases, which may host topological order, fractionalization, and non-Abelian statistics. Within some Kondo insulators, the hybridization gap is predicted to protect a nontrivial topological invariant and to harbor emergent heavy Dirac fermion surface modes. We use high-energy-resolution spectroscopic imaging in real and momentum space on the Kondo insulator, SmB$_6$. On cooling through $T^*_{\Delta}\approx$ 35 K we observe the opening of an insulating gap that expands to $\Delta\approx$ 10 meV at 2 K. Within the gap, we image the formation of linearly dispersing surface states with effective masses reaching $m^* = (410\pm20)m_e$. We thus demonstrate existence of a strongly correlated topological Kondo insulator phase hosting the heaviest known Dirac fermions.
- arXiv:1812.09643 (replaced) [pdf, other]
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Title: Few-electrode design for silicon MOS quantum dotsComments: main text + references is 6 pages and contains 5 figures; supplementary material is appendedJournal-ref: Semiconductor Science and Technology 35, 015002 (2019)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Silicon metal-oxide-semiconductor (MOS) spin qubits have become a promising platform for quantum information processing, with recent demonstrations of high-fidelity single and two-qubit gates. To move beyond a few qubits, however, more scalable designs that reduce the fabrication complexity and electrode density are needed. Here, we introduce a two-metal-layer MOS quantum dot device in which tunnel barriers are naturally formed by gaps between electrodes and controlled by adjacent accumulation gates. The accumulation gates define the electron reservoirs and provide tunability of the tunnel rate of nearly 8.5 decades/V, determined by a combination of charge sensor electron counting measurements and by direct transport. The valley splitting in the few-electron regime is probed by magneto-spectroscopy up to a field of 6 T, providing an estimate for the ground-state gap of 290 $\mu$eV. We show preliminary characterization of a double quantum dot, demonstrating that this design can be extended to linear dot arrays that should be useful in applications like electron shuttling. These results motivate further innovations in MOS quantum dot design that can improve the scalability prospects for spin qubits.
- arXiv:1901.05952 (replaced) [pdf, other]
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Title: Revealing multiple classes of stable quantum emitters in hexagonal boron nitride with correlated cathodoluminescence, photoluminescence, and strain mappingAuthors: Fariah Hayee, Leo Yu, Jingyuan Linda Zhang, Christopher J. Ciccarino, Minh Nguyen, Ann F Marshall, Igor Aharonovich, Jelena Vučković, Prineha Narang, Tony F. Heinz, Jennifer A DionneSubjects: Materials Science (cond-mat.mtrl-sci)
Single photon emitters (SPEs) in solids have emerged as promising candidates for quantum photonic sensing, communications, and computing. Defects in hexagonal boron nitride (hBN) exhibit high-brightness, room-temperature quantum emission, but their large spectral variability and unknown local structure significantly challenge their technological utility. Here, we directly correlate hBN quantum emission with the material's local strain using a combination of photoluminescence (PL), cathodoluminescence (CL) and nano-beam electron diffraction. Across 40 emitters and 15 samples, we observe zero phonon lines(ZPLs) in PL and CL ranging from 540-720 nm. CL mapping reveals that multiple defects and distinct defect species located within an optically-diffraction-limited region can each contribute to the observed PL spectra. Local strain maps indicate that strain is not required to activate the emitters and is not solely responsible for the observed ZPL spectral range. Instead, four distinct defect classes are responsible for the observed emission range. One defect class has ZPLs near 615 nm with predominantly matched CL-PL responses; it is not a strain-tuned version of another defect class with ZPL emission centered at 580 nm. A third defect class at 650 nm has low visible-frequency CL emission; and a fourth defect species centered at 705 nm has a small, ~10 nm shift between its CL and PL peaks. All studied defects are stable upon both electron and optical irradiation. Our results provide an important foundation for atomic-scale optical characterization of color centers, as well as a foundation for engineering defects with precise emission properties.
- arXiv:1901.10988 (replaced) [pdf]
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Title: Propagation of Spin Waves Through an Interface Between Ferromagnetic and Antiferromagnetic MaterialsComments: 5 pages, 3 figures, presented on ICSM 2018 conferenc in Antalya, Turkey, submitted to Journal of Superconductivity and Novel MagnetismSubjects: Applied Physics (physics.app-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Boundary conditions for order parameters at an interface between ferromagnetic (FM) and two-sublattice antiferromagnetic (AFM) materials were obtained in the continuous medium approximation similarly to the approach which allows one to take into account the finite thickness of the FM/FM interface, which is much less than spin wave length. Three order parameters are considered inside an interface of finite thickness with the magnetization $\mathbf{\text{M}}$ of FM, magnetizations of both sublattices $\mathbf{\text{M}}_{1}$ and $\mathbf{\text{M}}_{2}$ of AFM. The uniform and non-uniform exchange between all order parameters are taken into account to the interface energy. Using these boundary conditions, the excitation of a surface evanescent spin wave is considered in AFM when the spin wave in FM falls onto this interface. The coefficients and the phases of transmission and reflection of spin wave through the FM/AFM interface are derived.
- arXiv:1903.00552 (replaced) [pdf, other]
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Title: One-Component Order Parameter in URu$_2$Si$_2$ Uncovered by Resonant Ultrasound Spectroscopy and Machine LearningAuthors: Sayak Ghosh, Michael Matty, Ryan Baumbach, Eric D. Bauer, K. A. Modic, Arkady Shekhter, J. A. Mydosh, Eun-Ah Kim, B. J. RamshawJournal-ref: Sci. Adv. 6, eaaz4074 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el); Data Analysis, Statistics and Probability (physics.data-an)
The unusual correlated state that emerges in URu$_2$Si$_2$ below T$_{HO}$ = 17.5 K is known as "hidden order" because even basic characteristics of the order parameter, such as its dimensionality (whether it has one component or two), are "hidden". We use resonant ultrasound spectroscopy to measure the symmetry-resolved elastic anomalies across T$_{HO}$. We observe no anomalies in the shear elastic moduli, providing strong thermodynamic evidence for a one-component order parameter. We develop a machine learning framework that reaches this conclusion directly from the raw data, even in a crystal that is too small for traditional resonant ultrasound. Our result rules out a broad class of theories of hidden order based on two-component order parameters, and constrains the nature of the fluctuations from which unconventional superconductivity emerges at lower temperature. Our machine learning framework is a powerful new tool for classifying the ubiquitous competing orders in correlated electron systems.
- arXiv:1904.03925 (replaced) [pdf]
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Title: Unfolding force definition and the unified model for the mean unfolding force dependence on the loading rateAuthors: Rafayel PetrosyanComments: 48 pages, 8 figuresJournal-ref: J. Stat. Mech. (2020) 033201Subjects: Biological Physics (physics.bio-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Soft Condensed Matter (cond-mat.soft); Statistical Mechanics (cond-mat.stat-mech); Chemical Physics (physics.chem-ph)
In single-molecule force spectroscopy experiments, the dependence of the mean unfolding force on the loading rate is used for obtaining information about the energetic and dynamic properties of the system under study. However, it is crucial to understand that different dynamic force spectroscopy (DFS) models are applicable in different regimes, and that different definitions of the unfolding force might be used in those models. Here, for the first time, we discuss three definitions of the unfolding force. We carried out Brownian dynamics simulations in order to demonstrate the difference between these definitions and compare DFS models. Importantly, we derive the dependence of the mean unfolding force for the whole range of the loading rates by unifying three previously reported DFS models. Among the currently available models, this unified model shows the best agreement with the simulated data.
- arXiv:1904.04711 (replaced) [pdf, other]
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Title: Phonon-assisted Photoluminescence from Dark Excitons in Monolayers of Transition Metal DichalcogenidesAuthors: Samuel Brem, August Ekman, Dominik Christiansen, Florian Katsch, Malte Selig, Cedric Robert, Xavier Marie, Bernhard Urbaszek, Andreas Knorr, Ermin MalicJournal-ref: Nano Lett. 2020, 20, 4, 2849-2856Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci)
The photoluminescence (PL) spectrum of transition metal dichalcogenides (TMDs) shows a multitude of emission peaks below the bright exciton line and not all of them have been explained yet. Here, we study the emission traces of phonon-assisted recombinations of momentum-dark excitons. To this end, we develop a microscopic theory describing simultaneous exciton, phonon and photon interaction and including consistent many-particle dephasing. We explain the drastically different PL below the bright exciton in tungsten- and molybdenum-based materials as result of different configurations of bright and dark states. In good agreement with experiments, we show that WSe$_2$ exhibits clearly visible low-temperature PL signals stemming from the phonon-assisted recombination of momentum-dark excitons.
- arXiv:1904.13374 (replaced) [pdf, other]
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Title: Scalable Majorana vortex modes in iron-based superconductorsComments: 10 pages, 7 figures, Supplementary InformationJournal-ref: Science Advances Vol. 6, no. 9, eaay0443 (2020)Subjects: Superconductivity (cond-mat.supr-con); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
A vortex in an s-wave superconductor with a surface Dirac cone can trap a Majorana bound state with zero energy leading to a zero-bias peak (ZBP) of tunneling conductance. The iron-based superconductor FeTe$_x$Se$_{1-x}$ is one of the material candidates hosting these Majorana vortex modes. It has been observed by recent scanning tunneling spectroscopy measurement that the fraction of vortex cores possessing ZBPs decreases with increasing magnetic field on the surface of this iron-based superconductor. We construct a three-dimensional tight-binding model simulating the physics of over a hundred Majorana vortex modes in FeTe$_x$Se$_{1-x}$ with realistic physical parameters. Our simulation shows that the Majorana hybridization and disordered vortex distribution can explain the decreasing fraction of the ZBPs observed in the experiment. Furthermore, we find the statistics of the energy peaks off zero energy in our simulation with the Majorana physics in agreement with the analyzed peak statistics in the vortex cores from the experiment. This agreement and the explanation of the decreasing ZBP fraction lead to an important indication of scalable Majorana vortex modes in the iron-based superconductor. Thus, FeTe$_x$Se$_{1-x}$ can be one promising platform possessing scalable Majorana qubits for quantum computing. In addition, we further show the interplay of the ZBP presence and the vortex locations qualitatively agrees with our additional experimental observation and predict the universal spin signature of the hybridized multiple Majorana vortex modes.
- arXiv:1905.06578 (replaced) [pdf, ps, other]
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Title: Application of Onsager Machlup integral in solving dynamic equations in non-equilibrium systemsComments: 25 pages, 7 figures, submitted to Phys. Rev. EJournal-ref: Phys. Rev. E 99, 063303 (2019)Subjects: Soft Condensed Matter (cond-mat.soft)
In 1931, Onsager proposed a variational principle which has become the base of many kinetic equations for non-equilibrium systems. We have been showing that this principle is useful in obtaining approximate solutions for the kinetic equations, but our previous method has a weakness that it can be justified, strictly speaking, only for small incremental time. Here we propose an improved method which does not have this drawback. The new method utilizes the integral proposed by Onsager and Machlup in 1953, and can tell us which of the approximate solutions is the best solution without knowing the exact solution. The new method has an advantage that it allows us to determine the steady state in non-equilibrium system by a variational calculus. We demonstrate this using three examples, (a) simple diffusion problem, (b) capillary problem in a tube with corners, and (c) free boundary problem in liquid coating, for which the kinetic equations are written in second or fourth order partial differential equations.
- arXiv:1905.08384 (replaced) [pdf, other]
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Title: Some ground-state expectation values for the free parafermion Z(N) spin chainComments: 17 pages, 4 figures; extra referencesJournal-ref: J. Stat. Mech. (2019) 124002Subjects: Statistical Mechanics (cond-mat.stat-mech); Strongly Correlated Electrons (cond-mat.str-el); Mathematical Physics (math-ph); Quantum Physics (quant-ph)
We consider the calculation of ground-state expectation values for the non-Hermitian Z(N) spin chain described by free parafermions. For N=2 the model reduces to the quantum Ising chain in a transverse field with open boundary conditions. Use is made of the Hellmann-Feynman theorem to obtain exact results for particular single site and nearest-neighbour ground-state expectation values for general N which are valid for sites deep inside the chain. These results are tested numerically for N=3, along with how they change as a function of distance from the boundary.
- arXiv:1906.00070 (replaced) [pdf]
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Title: Sensitivity of the Power Spectra of Magnetization Fluctuations in Low Barrier Nanomagnets to Barrier Height Modulation and DefectsJournal-ref: SPIN, 2050001 (2019)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Statistical Mechanics (cond-mat.stat-mech)
Nanomagnets with small shape anisotropy energy barriers on the order of the thermal energy have unstable magnetization that fluctuates randomly in time. They have recently emerged as promising hardware platforms for stochastic computing and machine learning because the random magnetization states can be harnessed for probabilistic bits. Here, we have studied how the statistics of the magnetization fluctuations (e.g. the power spectral density) is affected by (i) moderate variations in the barrier height of the nanomagnet and (ii) the presence of structural defects, in order to assess how robust the computing platform is. We found that the power spectral density is relatively insensitive to moderate barrier height change and also relatively insensitive to the presence of small localized defects. However, extended (delocalized) defects, such as thickness variations over a significant fraction of the nanomagnet, affect the power spectral density very noticeably. As a result, small variations in the shape (causing small variations in the barrier height), or small localized defects, are relatively innocuous and tolerable, but significant variation of the nanomagnet thickness is not. Consequently, tight control over the nanomagnet thickness must be maintained for stochastic computing applications.
- arXiv:1906.03484 (replaced) [pdf, other]
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Title: Interevent time distribution, burst, and hybrid percolation transitionJournal-ref: Chaos 29, 091102 (2019)Subjects: Statistical Mechanics (cond-mat.stat-mech)
Critical phenomena of a second-order percolation transition are known to be independent of cluster merging or pruning process. However, those of a hybrid percolation transition (HPT), mixed properties of both first-order and second-order transitions, depend on the processes. The HPT induced by cluster merging is more intrigue and little understood than the other. Here, we construct a theoretical framework using the so-called restricted percolation model. In this model, clusters are ranked by size and partitioned into small- and large-cluster sets. As the cluster rankings are updated by cluster coalescence, clusters may move back and forth across the set boundary. The inter-event time (IET) between two consecutive crossing times have two distributions with power-law decays, which in turn characterize the criticality of the HPT. A burst of such crossing events occurs and signals the upcoming transition. We discuss a related phenomenon to this critical dynamics.
- arXiv:1906.04945 (replaced) [pdf]
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Title: Unfolding the complexity of quasi-particle physics in disordered materialsAuthors: Sai Mu, Raina Olsen, B. Dutta, L. Lindsay, G. D. Samolyuk, T. Berlijn, E. D. Specht, K. Jin, H. Bei, T. Hickel, B. C. Larson, G. M. StocksComments: 25 pages, 6 figuresJournal-ref: npj Computational Materials, 6, 4 (2020)Subjects: Materials Science (cond-mat.mtrl-sci)
The concept of quasi-particles forms the theoretical basis of our microscopic understanding of emergent phenomena associated with quantum mechanical many-body interactions. However, quasi-particle theory in disordered materials has proven difficult, resulting in the predominance of mean-field solutions. Here we report first-principles phonon calculations and inelastic x-ray and neutron scattering measurements on equiatomic alloys (NiCo, NiFe, AgPd, and NiFeCo) with force constant dominant disorder - confronting a key 50-year-old assumption in the Hamiltonian of all mean-field quasi-particle solutions for off-diagonal disorder. Our results have revealed the presence of a large, and heretofore unrecognized, impact of local chemical environments on the distribution of the species-pair-resolved force constant disorder that can dominate phonon scattering. This discovery not only identifies a critical analysis issue that has broad implications for other elementary excitations such as magnons and skyrmions in magnetic alloys, but also provides an important tool for the design of materials with ultra-low thermal conductivity.
- arXiv:1908.00959 (replaced) [pdf]
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Title: Quantifying Exchange Forces of a Non-Collinear Magnetic Structure on the Atomic ScaleAuthors: Nadine Hauptmann, Soumyajyoti Haldar, Tzu-Chao Hung, Wouter Jolie, Mara Gutzeit, Daniel Wegner, Stefan Heinze, Alexander A. KhajetooriansSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
The large interest in chiral magnetic structures for realization of nanoscale magnetic storage or logic devices has necessitated methods which can quantify magnetic interactions at the atomic scale. To overcome the limitations of the typically used current-based sensing of atomic-scale exchange interactions, a force-based detection scheme is highly advantageous. Here, we quantify the atomic-scale exchange force field between a ferromagnetic tip and a cycloidal spin spiral using our developed combination of current and exchange force detection. Compared to the surprisingly weak spin polarization, the exchange force field is more sensitive to atomic-scale variations in the magnetization. First-principles calculations reveal that the measured atomic-scale variations in the exchange force originate from different contributions of direct and indirect (Zener) type exchange mechanisms, depending on the chemical tip termination. Our work opens the perspective of quantifying different exchange mechanisms of chiral magnetic structures with atomic-scale precision using 3D magnetic exchange force field measurements.
- arXiv:1909.06113 (replaced) [pdf, other]
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Title: Pre-Cooling Strategy Allows Exponentially Faster HeatingComments: Supp. Info. is attached as a separated fileJournal-ref: Phys. Rev. Lett. 124, 060602 (2020)Subjects: Statistical Mechanics (cond-mat.stat-mech)
What is the fastest way to heat a system which is coupled to a temperature controlled oven? The intuitive answer is to use only the hottest temperature available. However, we show that often it is possible to achieve an exponentially faster heating, and propose a strategy to find the optimal protocol. Surprisingly, this protocol can have a pre-cooling stage -- cooling the system before heating it shortens the heating time significantly. This approach can be applied to many-body systems, as we demonstrate in the 2D antiferromagnet Ising model.
- arXiv:1909.13828 (replaced) [pdf, other]
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Title: Nonequilibrium thermodynamics of erasure with superconducting flux logicAuthors: Olli-Pentti Saira, Matthew H. Matheny, Raj Katti, Warren Fon, Gregory Wimsatt, James P. Crutchfield, Siyuan Han, Michael L. RoukesComments: 9 pages, 7 figuresJournal-ref: Phys. Rev. Research 2, 013249 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We implement a thermal-fluctuation driven logical bit reset on a superconducting flux logic cell. We show that the logical state of the system can be continuously monitored with only a small perturbation to the thermally activated dynamics at 500 mK. We use the trajectory information to derive a single-shot estimate of the work performed on the system per logical cycle. We acquire a sample of $10^5$ erasure trajectories per protocol, and show that the work histograms agree with both microscopic theory and global fluctuation theorems. The results demonstrate how to design and diagnose complex, high-speed, and thermodynamically efficient computing using superconducting technology.
- arXiv:1909.13854 (replaced) [pdf, other]
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Title: van der Waals metamaterialsJournal-ref: Phys. Rev. B 101, 121103 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci)
The van der Waals heterostructures are a fertile frontier for discovering emergent phenomena in condensed matter systems. They are constructed by stacking elements of a large library of two-dimensional materials, which couple together through van der Waals interactions. However, the number of possible combinations within this library is staggering, and fully exploring their potential is a daunting task. Here we introduce van der Waals metamaterials to rapidly prototype and screen their quantum counterparts. These layered metamaterials are designed to reshape the flow of ultrasound to mimic electron motion. In particular, we show how to construct analogues of all stacking configurations of bilayer and trilayer graphene through the use of interlayer membranes that emulate van der Waals interactions. By changing the membrane's density and thickness, we reach coupling regimes far beyond that of conventional graphene. We anticipate that van der Waals metamaterials will explore, extend, and inform future electronic devices. Equally, they allow the transfer of useful electronic behavior to acoustic systems, such as flat bands in magic-angle twisted bilayer graphene, which may aid the development of super-resolution ultrasound imagers.
- arXiv:1910.04842 (replaced) [pdf]
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Title: Robustness and scalability of p-bits implemented with low energy barrier nanomagnetsComments: Accepted for publication in IEEE Magnetics LettersJournal-ref: IEEE Magnetics Letters, 10, 4510404 (2019)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Applied Physics (physics.app-ph)
Probabilistic (p-) bits implemented with low energy barrier nanomagnets (LBMs) have recently gained attention because they can be leveraged to perform some computational tasks very efficiently. Although more error-resilient than Boolean computing, p-bit based computing employing LBMs is, however, not completely immune to defects and device-to-device variations. In some tasks (e.g. binary stochastic neurons for machine learning and p-bits for population coding), extended defects, such as variation of the LBM thickness over a significant fraction of the surface, can impair functionality. In this paper, we have examined if unavoidable geometric device-to-device variations can have a significant effect on one of the most critical requirements for probabilistic computing, namely the ability to "program" probability with an external agent, such as a spin-polarized current injected into the LBM. We found that the programming ability is fortunately not lost due to reasonable device-to-device variations. The little variation in the probability versus current characteristic that reasonable device variability causes can be suppressed further by increasing the spin polarization of the current. This shows that probabilistic computing with LBMs is robust against small geometric variations, and hence will be "scalable" to a large number of p-bits.
- arXiv:1910.07710 (replaced) [pdf]
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Title: Phonon renormalization induced by electric field in ferroelectric P(VDF-TrFE) nanofibersJournal-ref: Phys. Rev. Applied 13, 034019 (2020)Subjects: Materials Science (cond-mat.mtrl-sci); Soft Condensed Matter (cond-mat.soft)
We report phonon renormalization induced by an external electric field E in ferroelectric poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] nanofibers through measuring the E-dependent thermal conductivity. Our experimental results are in excellent agreement with the theoretical ones derived from the lattice dynamics. The renormalization is attributed to the anharmonicity that modifies the phonon spectrum when the atoms are pulled away from their equilibrium positions by the electric field. Our finding provides an efficient way to manipulate the thermal conductivity by tuning external fields in ferroelectric materials.
- arXiv:1910.09509 (replaced) [pdf]
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Title: Rapid, Quantitative Therapeutic Screening for Alzheimer's Enzymes Enabled by Optimal Signal Transduction with TransistorsAuthors: Son T. Le, Michelle A. Morris, Antonio Cardone, Nicholas B. Guros, Jeffery B. Klauda, Brent A. Sperling, Curt A. Richter, Harish C. Pant, Arvind BalijepalliSubjects: Applied Physics (physics.app-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Quantitative Methods (q-bio.QM)
We show that simple, commercially sourced n-channel silicon field-effect transistors (nFETs) operating under closed loop control exhibit an ~3-fold improvement in pH readout resolution to (7.2+/-0.3)x10^-3 at a bandwidth of 10 Hz when compared with the open loop operation commonly employed by integrated ion-sensitive field-effect transistors (ISFETs). We leveraged the improved nFET performance to measure the change in solution pH arising from the activity of a pathological form of the kinase Cdk5, an enzyme implicated in Alzheimer's disease, and showed quantitative agreement with previous measurements. The improved pH resolution was realized while the devices were operated in a remote sensing configuration with the pH sensing element off-chip and connected electrically to the FET gate terminal. We compared these results with those measured by using a custom-built dual-gate 2D field-effect transistor (dg2DFET) fabricated with 2D semi-conducting MoS2 channels and a moderate device gain, alpha=8. Under identical solution conditions the pH resolution of the nFETs was only 2-fold worse than the dg2DFETs pH resolution of (3.9+/-0.7)x10^-3. Finally, using the nFETs, we demonstrated the effectiveness of a custom polypeptide, p5, as a therapeutic agent in restoring the function of Cdk5. We expect that the straight-forward modifications to commercially sourced nFETs demonstrated here will lower the barrier to widespread adoption of these remote-gate devices and enable sensitive bioanalytical measurements for high throughput screening in drug discovery and precision medicine applications.
- arXiv:1910.10126 (replaced) [pdf, other]
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Title: Modification of electron-phonon coupling by micromachining and suspensionComments: 9 pages, 6 figuresJournal-ref: J Appl. Phys. 127, 024307 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Weak electron-phonon interaction in metals at low temperatures forms the basis of operation for cryogenic hot-electron bolometers and calorimeters. Standard power laws, describing the heat flow in the majority of experiments, have been identified and derived theoretically. However, a full picture encompassing experimentally relevant effects such as reduced dimensionality, material interfaces, and disorder is in its infancy, and has not been tested extensively. Here, we study the electron-phonon heat flow in a thin gold film on a SiO${}_2$ platform below 100 mK using supercurrent thermometry. We find the power law exponent to be modified from 5.1 to 4.6 as the platform is micromachined and released from its substrate. We attribute this change to a modified phonon spectrum. The findings are compared to past experiments and theoretical models.
- arXiv:1910.12525 (replaced) [pdf, other]
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Title: Observation of quantum Hall interferometer phase jumps due to changing quasiparticle numberAuthors: Marc P. Röösli (1), Lars Brem (1), Benedikt Kratochwil (1), Giorgio Nicolí (1), Beat A. Braem (1), Szymon Hennel (1), Peter Märki (1), Matthias Berl (1), Christian Reichl (1), Bernd Rosenow (2), Werner Wegscheider (1), Klaus Ensslin (1), Thomas Ihn (1) ((1) Solid State Physics Laboratory, Department of Physics, ETH Zurich, Switzerland, (2) Institute for Theoretical Physics, Leipzig University, Leipzig, Germany)Comments: 12 pages, 6 figuresJournal-ref: Phys. Rev. B 101, 125302 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We measure the magneto-conductance through a micron-sized quantum dot hosting about 500 electrons in the quantum Hall regime. In the Coulomb blockade, when the island is weakly coupled to source and drain contacts, edge reconstruction at filling factors between one and two in the dot leads to the formation of two compressible regions tunnel coupled via an incompressible region of filling factor $\nu=1$. We interpret the resulting conductance pattern in terms of a phase diagram of stable charge in the two compressible regions. Increasing the coupling of the dot to source and drain, we realize a Fabry-P\'{e}rot quantum Hall interferometer, which shows an interference pattern strikingly similar to the phase diagram in the Coulomb blockade regime. We interpret this experimental finding using an empirical model adapted from the Coulomb blockaded to the interferometer case. The model allows us to relate the observed abrupt jumps of the Fabry-P\'{e}rot interferometer phase to a change in the number of bulk quasiparticles. This opens up an avenue for the investigation of phase shifts due to (fractional) charge redistributions in future experiments on similar devices.
- arXiv:1910.12750 (replaced) [pdf]
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Title: Deep-Learning-Based Image Segmentation Integrated with Optical Microscopy for Automatically Searching for Two-Dimensional MaterialsAuthors: Satoru Masubuchi, Eisuke Watanabe, Yuta Seo, Shota Okazaki, Takao Sasagawa, Kenji Watanabe, Takashi Taniguchi, Tomoki MachidaJournal-ref: npj 2D Mater Appl 4, 3 (2020)Subjects: Image and Video Processing (eess.IV); Materials Science (cond-mat.mtrl-sci)
Deep-learning algorithms enable precise image recognition based on high-dimensional hierarchical image features. Here, we report the development and implementation of a deep-learning-based image segmentation algorithm in an autonomous robotic system to search for two-dimensional (2D) materials. We trained the neural network based on Mask-RCNN on annotated optical microscope images of 2D materials (graphene, hBN, MoS2, and WTe2). The inference algorithm is run on a 1024 x 1024 px2 optical microscope images for 200 ms, enabling the real-time detection of 2D materials. The detection process is robust against changes in the microscopy conditions, such as illumination and color balance, which obviates the parameter-tuning process required for conventional rule-based detection algorithms. Integrating the algorithm with a motorized optical microscope enables the automated searching and cataloging of 2D materials. This development will allow researchers to utilize unlimited amounts of 2D materials simply by exfoliating and running the automated searching process.
- arXiv:1910.14301 (replaced) [pdf, other]
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Title: Dynamical generation of Majorana edge-correlations in a ramped Kitaev chain coupled to non-thermal dissipative channelsComments: 12 pages, 3 figuresJournal-ref: Phys. Rev. B 101, 104307 (2020)Subjects: Statistical Mechanics (cond-mat.stat-mech); Quantum Physics (quant-ph)
We quantitatively study the out-of-equilibrium edge Majorana correlation in a linearly ramped 1D Kitaev chain of finite length in a dissipative environment. The chemical potential is dynamically ramped to drive the chain from its topologically trivial to non-trivial phase in the presence of couplings to non-thermal Markovian baths. We consider two distinctive situations: In the first situation, the bath is quasi local in the site basis (local in quasi-particle basis) while in the other it is local. Following a Lindbladian approach, we compute the early time dynamics as well as the asymptotic behavior of the edge-Majorana correlation to probe the interplay between two competing time scales, one due to the coherent ramping while the other is due to the dissipative coupling. For the quasi-local bath, we establish that there is a steady generation of Majorana correlations in asymptotic time and the presence of an optimal ramping time which facilitates a quicker approach to the topological steady state. In the second scenario, we analyse the action of a local particle-loss type of bath in which we have established the existence of an optimal ramping time which results from the competing dynamics between the unitary ramp and the dissipative coupling. While the defect generated by the former decays exponentially with increasing ramp duration, the later scales linearly with the same. This linear scaling is further established through a perturbation theory formulated using the non-dimensionalised coupling to the bath as a small parameter.
- arXiv:1911.06184 (replaced) [pdf, other]
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Title: Hybrid functional calculations of electronic structure and carrier densities in rare-earth monopnictidesJournal-ref: Phys. Rev. B 101, 125105 (2020)Subjects: Materials Science (cond-mat.mtrl-sci)
The structural parameters and electronic structure of rare-earth pnictides are calculated using density functional theory (DFT) with the Heyd, Scuseria, and Ernzerhof (HSE06) screened hybrid functional. We focus on RE-V compounds, with RE=La, Gd, Er, and Lu, and V=As, Sb, and Bi, and analyze the effects of spin-orbit coupling and treating the RE 4$f$ electrons as valence electrons in the projector augmented wave approach. The results of HSE06 calculations are compared with DFT within the generalized gradient approximation (DFT-GGA) and other previous calculations. We find that all these RE-V compounds are semimetals with electron pockets at the $X$ point and hole pockets at $\Gamma$. Whereas in DFT-GGA the carrier density is significantly overestimated, the computed carrier densities using HSE06 is in good agreement with the available experimental data.
- arXiv:1911.08611 (replaced) [pdf]
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Title: Effect of sodium pyrophosphate and understanding microstructure of aqueous LAPONITE(R) dispersion using dissolution studySubjects: Materials Science (cond-mat.mtrl-sci); Soft Condensed Matter (cond-mat.soft)
We investigate physical origin of ergodicity breaking in an aqueous colloidal dispersion of synthetic hectorite clay, LAPONITE(R), by performing dissolution and rheological experiments with monovalent salt and tetrasodium pyrophosphate solution. We also study the effect of interface, nitrogen and paraffin oil on the same. Dissolution experiments carried out for dispersions with both the interfaces show similar results. However, for samples with nitrogen interface, all the effects are observed to get expedited in time compared to paraffin oil interface. When kept in contact with water, 1.5 wt. % and 2.8 wt. % colloidal dispersion at pH 10 swell at small ages, while do not swell at large ages. The solution of tetrasodium pyrophosphate, interestingly, dissolves the entire colloidal dispersion samples with pH 10 irrespective of the clay concentration. Experiments carried out on colloidal dispersions prepared in water having pH 13 demonstrate no effect of water as well as sodium pyrophosphate solution on the same suggesting a possibility of the presence of negative charge on edge at that pH. We believe that all the behaviors observed for samples at pH 10 can be explained by an attractive gel microstructure formed by edge-to-face contact. Furthermore, the absence of swelling in old colloidal dispersion at pH 10 and dissolution of the same by sodium pyrophosphate solution cannot be explained by merely repulsive interactions. This behavior suggests that attractive interactions play an important role in causing ergodicity breaking in the colloidal dispersions at pH 10 at all the ages irrespective of the clay concentration. We substantiate the presence of fractal network structure formed by interparticle edge-face association using rheological tools and cryo-TEM imaging. We also conduct a comprehensive study of the effect of sodium pyrophosphate in the sol-gel transition of LAPONITE(R) dispersion.
- arXiv:2001.02434 (replaced) [pdf, other]
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Title: Quantum oscillations probe the Fermi surface topology of the nodal-line semimetal CaAgAsAuthors: Y. H. Kwan, P. Reiss, Y. Han, M. Bristow, D. Prabhakaran, D. Graf, A. McCollam, S. A. Parameswaran, A. I. ColdeaComments: accepted Physical Review Research; 12 pages, 10 figures including supplemental materialsJournal-ref: Phys. Rev. Research 2, 012055 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el); Materials Science (cond-mat.mtrl-sci)
Nodal semimetals are a unique platform to explore topological signatures of the unusual band structure that can manifest by accumulating a nontrivial phase in quantum oscillations. Here we report a study of the de Haasvan Alphen oscillations of the candidate topological nodal line semimetal CaAgAs using torque measurements in magnetic fields up to 45 T. Our results are compared with calculations for a toroidal Fermi surface originating from the nodal ring. We find evidence of a nontrivial Berry phase shift only in one of the oscillatory frequencies. We interpret this as a Berry phase arising from the semi-classical electronic Landau orbit which links with the nodal ring when the magnetic field lies in the mirror (ab) plane. Furthermore, additional Berry phase accumulates while rotating the magnetic field for the second orbit in the same orientation which does not link with the nodal ring. These effects are expected in CaAgAs due to the lack of inversion symmetry. Our study experimentally demonstrates that CaAgAs is an ideal platform for exploring the physics of nodal line semimetals and our approach can be extended to other materials in which trivial and nontrivial oscillations are present.
- arXiv:2001.05611 (replaced) [pdf, other]
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Title: Control of polymorphism during epitaxial growth of hyperferroelectric candidate LiZnSb on GaSb (111)BAuthors: Dongxue Du, Patrick J. Strohbeen, Hanjong Paik, Chenyu Zhang, Konrad Genser, Karin M. Rabe, Paul M. Voyles, Darrell G. Schlom, Jason K. KawasakiComments: The following article has been submitted to the Journal of Vacuum Science and Technology. After it is published, it will be found at this https URLJournal-ref: Journal of Vacuum Science & Technology B 38, 022208 (2020)Subjects: Materials Science (cond-mat.mtrl-sci)
A major challenge for ferroelectric devices is the depolarization field, which competes with and often destroys long-range polar order in the limit of ultrathin films. Recent theoretical predictions suggest a new class of materials, termed hyperferroelectics, that should be robust against the depolarization field and enable ferroelectricity down to the monolayer limit. Here we demonstrate the epitaxial growth of hexagonal LiZnSb, one of the hyperferroelectric candidate materials, by molecular-beam epitaxy on GaSb (111)B substrates. Due to the high volatility of all three atomic species, we find that LiZnSb can be grown in an adsorption-controlled window, using an excess zinc flux. Within this window, the desired polar hexagonal phase is stabilized with respect to a competing cubic polymorph, as revealed by X-ray diffraction and transmission electron microscopy measurements. First-principles calculations show that for moderate amounts of epitaxial strain and moderate concentrations of Li vacancies, the cubic LiZnSb phase is lower in formation energy than the hexagonal phase, but only by a few meV per formula unit. Therefore we suggest that kinetics plays a role in stabilizing the desired hexagonal phase at low temperatures. Our results provide a path towards experimentally demonstrating ferroelectricity and hyperferroelectricity in a new class of ternary intermetallic compounds.
- arXiv:2001.07954 (replaced) [pdf]
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Title: The design of eutectic high entropy alloys in Al-Co-Cr-Fe-Ni systemAuthors: Ali ShafieiComments: 32 Pages, 10 FiguresJournal-ref: Metals and Materials International (2020)Subjects: Materials Science (cond-mat.mtrl-sci)
In the present work, a simple approach is proposed for predicting the compositions of eutectic high entropy alloys (EHEAs) in Al-Co-Cr-Fe-Ni system. It is proposed that eutectic lines exist between certain eutectic alloys in this system and, as a result, new eutectic or near-eutectic compositions can be obtained by mixing the alloys which are located on the same eutectic line. The approach is applied for a series of experimentally verified eutectic alloys and new eutectic or near-eutectic alloys are designed for Al-Co-Cr-Fe-Ni system. Furthermore, by investigating the compositions of verified eutectic alloys in Al-Co-Cr-Fe-Ni system, compositional diagrams are proposed which show the relations between the concentrations of constituent elements in eutectic alloys. The compositional diagrams suggest that EHEAs are derived from binary and ternary eutectic alloys. Moreover, the proposed diagrams can be considered as convenient methods for evaluating the composition of EHEAs in Al-Co-Cr-Fe-Ni system.
- arXiv:2002.00183 (replaced) [pdf, ps, other]
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Title: Theory of spin-polarized superconductors -- an analogue of superfluid $^3$He A-phaseAuthors: Kazushige MachidaComments: 6 pages, 2 figuresJournal-ref: J. Phys. Soc. Jpn., 89, 033702 (2020)Subjects: Superconductivity (cond-mat.supr-con); Strongly Correlated Electrons (cond-mat.str-el)
It is shown theoretically that ferromagnetic superconductors, UGe$_2$, URhGe, and UCoGe can be described in terms of the A-phase like triplet pairing similar to superfluid $^3$He in a unified way, including peculiar reentrant, S-shape, or L-shape $H_{\rm c2}$ curves. The associated double transition inevitable between the A$_1$ and A$_2$-phases in the $H$-$T$ plane is predicted, both of which are characterized by non-unitary state with broken time reversal symmetry and the half-gap. UTe$_2$, which has been discovered quite recently to be a spin-polarized superconductor, is analyzed successively in the same view point, pointing out that the expected A$_1$-A$_2$ transition is indeed emerging experimentally. Thus the four heavy Fermion compounds all together are entitled to be topologically rich solid state materials worth further investigating together with superfluid $^3$He A-phase.
- arXiv:2002.05074 (replaced) [pdf]
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Title: Intersubband transition engineering in the conduction band of asymmetric coupled Ge/SiGe quantum wellsAuthors: Luca Persichetti, Michele Montanari, Chiara Ciano, Luciana Di Gaspare, Michele Ortolani, Leonetta Baldassarre, Marvin H. Zoellner, Samik Mukherjee, Oussama Moutanabbir, Giovanni Capellini, Michele Virgilio, Monica De SetaJournal-ref: Crystals 2020, 10(3), 179Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci); Other Condensed Matter (cond-mat.other)
: n-type Ge/SiGe asymmetric-coupled quantum wells represent the building block of a variety of nanoscale quantum devices, including recently proposed designs for a silicon-based THz quantum cascade laser. In this paper, we combine structural and spectroscopic experiments on 20-module superstructures, each featuring two Ge wells coupled through a Ge-rich tunnel barrier, as a function of the geometry parameters of the design and the P dopant concentration. Through the comparison of THz spectroscopic data with numerical calculations of intersubband optical absorption resonances, we demonstrated that it is possible to tune by design the energy and the spatial overlap of quantum confined subbands in the conduction band of the heterostructures. The high structural/interface quality of the samples and the control achieved on subband hybridization are the promising starting point towards a working electrically pumped light-emitting device.
- arXiv:2002.09074 (replaced) [pdf, ps, other]
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Title: Coarse-Graining of Microscopic Dynamics into Mesoscopic Transient Potential ModelAuthors: Takashi UneyamaComments: 25 pages, 3 figures, to appear in Phys. Rev. EJournal-ref: Phys. Rev. E 101, 032106 (2020)Subjects: Statistical Mechanics (cond-mat.stat-mech); Soft Condensed Matter (cond-mat.soft)
We show that a mesoscopic coarse-grained dynamics model which incorporates the transient potential can be formally derived from an underlying microscopic dynamics model. As a microscopic dynamics model, we employ the overdamped Langevin equation. By utilizing the path probability and the Onsager-Machlup type action, we calculate the path probability for the coarse-grained mesoscopic degrees of freedom. The action for the mesoscopic degrees of freedom can be simplified by incorporating the transient potential. Then the dynamic equation for the mesoscopic degrees of freedom can be simply described by the Langevin equation with the transient potential (LETP). As a simple and analytically tractable approximation, we introduce additional degrees of freedom which express the state of the transient potential. Then we approximately express the dynamics of the system as the the combination of the LETP and the dynamics model for the transient potential. The resulting dynamics model has the same dynamical structure as the responsive particle dynamics (RaPiD) type models [W. J. Briels, Soft Matter 5, 4401 (2009)] and the multi-chain slip-spring type models [T. Uneyama and Y. Masubuchi, J. Chem. Phys. 137, 154902 (2012)]. As a demonstration, we apply our coarse-graining method with the LETP to a single particle dynamics in a supercooled liquid, and compare the results of the LETP with the molecular dynamics simulations and other coarse-graining models.
- arXiv:2003.02564 (replaced) [pdf, other]
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Title: Realization and transport investigation of a single layer-twisted bilayer graphene junctionComments: 20 pages, 4 figuresJournal-ref: Carbon 163, 105-112 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We report on low-temperature transport study of a single layer graphene (SLG)-twisted bilayer graphene (tBLG) junction device. The SLG-tBLG junction in the device is grown by chemical vapor deposition and the device is fabricated in a Hall-bar configuration on Si/SiO$_2$ substrate. The longitudinal resistances across the SLG-tBLG junction (cross-junction resistances) on the two sides of the Hall bar and the Hall resistances of SLG and tBLG in the device are measured. In the quantum Hall regime, the measurements show that the measured cross-junction resistances exhibit a series of new quantized plateaus and the appearance of these resistance plateaus can be attributed to the presence of the well-defined edge-channel transport along the SLG-tBLG junction interface. The measurements also show that the difference between the cross-junction resistances measured on the two sides of the Hall-bar provides a sensitive measure to the edge channel transport characteristics in the two graphene layers that constitute the SLG-tBLG junction and to degeneracy lifting of the Landau levels in the tBLG layer. Temperature dependent measurements of the cross-junction resistance in the quantum Hall regime are also carried out and the influence of the transverse transport of the bulk Landau levels on the edge channel transport along the SLG-tBLG junction interface are extracted. These results enrich the understanding of the charge transport across interfaces in graphene hybrid structures and open up new opportunities for probing exotic quantum phenomena in graphene devices.
Crosses
- arXiv:1907.05170 (cross-list from physics.optics) [pdf]
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Title: Laser-Induced Spatially-Selective Tailoring of High-Index Dielectric MetasurfacesAuthors: Jonas Berzinš, Simonas Indrišiūnas, Stefan Fasold, Michael Steinert, Olga Žukovskaja, Dana Cialla-May, Paulius Gečys, Stefan M. B. Bäumer, Thomas Pertsch, Frank SetzpfandtJournal-ref: Optics Express 28 (2), 1539-1553 (2020)Subjects: Optics (physics.optics); Materials Science (cond-mat.mtrl-sci); Applied Physics (physics.app-ph)
Optically resonant high-index dielectric metasurfaces featuring Mie-type electric and magnetic resonances are usually fabricated by means of planar technologies, which limit the degrees of freedom in tunability and scalability of the fabricated systems. Therefore, we propose a complimentary post-processing technique based on ultrashort ($\leq$ 10 ps) laser pulses. The process involves thermal effects: crystallization and reshaping, while the heat is localized by a high-precision positioning of the focused laser beam. Moreover, for the first time, the resonant behavior of dielectric metasurface elements is exploited to engineer a specific absorption profile, which leads to a spatially-selective heating and a customized modification. Such technique has a potential to reduce the complexity in the fabrication of non-uniform metasurface-based optical elements. Two distinct cases, a spatial pixelation of a large-scale metasurface and a height modification of metasurface elements, are explicitly demonstrated.
- arXiv:2003.03112 (cross-list from cond-mat.dis-nn) [pdf, other]
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Title: Bounds on the entanglement entropy by the number entropy in non-interacting fermionic systemsAuthors: Maximilian Kiefer-Emmanouilidis (1 and 2), Razmik Unanyan (1), Jesko Sirker (2), Michael Fleischhauer (1) ((1) Department of Physics and Research Center OPTIMAS, University of Kaiserslautern, Kaiserslautern, Germany, (2) Department of Physics and Astronomy, University of Manitoba, Winnipeg, Canada)Subjects: Disordered Systems and Neural Networks (cond-mat.dis-nn); Quantum Gases (cond-mat.quant-gas); Statistical Mechanics (cond-mat.stat-mech); Strongly Correlated Electrons (cond-mat.str-el)
Entanglement in a pure state of a many-body system can be characterized by the R\'enyi entropies $S^{(\alpha)}=\ln\textrm{tr}(\rho^\alpha)/(1-\alpha)$ of the reduced density matrix $\rho$ of a subsystem. These entropies are, however, difficult to access experimentally and can typically be determined for small systems only. Here we show that for free fermionic systems in a Gaussian state and with particle number conservation, $\ln S^{(2)}$ can be tightly bound by the much easier accessible R\'enyi number entropy $S^{(2)}_N=-\ln \sum_n p^2(n)$ which is a function of the probability distribution $p(n)$ of the total particle number in the considered subsystem only. A dynamical growth in entanglement, in particular, is therefore always accompanied by a growth---albeit logarithmically slower---of the number entropy. We illustrate this relation by presenting numerical results for quenches in non-interacting one-dimensional lattice models including disorder-free, Anderson-localized, and critical systems with off-diagonal disorder.
Wed, 11 Mar 2020
- arXiv:2003.04312 [pdf, other]
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Title: Unraveling the magnetic interactions and spin state in insulating Sr$_{2-x}$La$_x$CoNbO$_6$Comments: submittedJournal-ref: Physical Review B, 101, 094434 (2020)Subjects: Materials Science (cond-mat.mtrl-sci); Strongly Correlated Electrons (cond-mat.str-el)
We investigate the structural, magnetic and spin-state transitions, and magnetocaloric properties of Sr$_{2-x}$La$_x$CoNbO$_6$ ($x=$ 0--1) double perovskites. The structural transition from tetragonal to monoclinic phase at $x$ $\geqslant$ 0.6, and an evolution of (101)/(103) superlattice reflections and Raman active modes indicate the enhancement in the B-site ordering with $x$. The magnetic susceptibility data reveal the transition from weak ferromagnetic (FM) to antiferromagnetic (AFM) ordering for $x$ $\geqslant$ 0.6 with T$_{\rm N}$$\approx$9--15~K. Interestingly, the La substitution drives towards more insulating state due to increase in high-spin Co$^{2+}$, whereas a spin-state crossover is observed in Co$^{3+}$ from high-spin to intermediate/low-spin states with $x$. We discuss the correlation between complex magnetic interactions and the presence of various Co spin-states in the system. Moreover, the emergence of metamagnetic nature due to the competition between FM and AFM interactions as well as crossover from conventional to inverse magnetocaloric effect have been demonstrated by detailed analysis of temperature and field dependent change in magnetic entropy.
- arXiv:2003.04324 [pdf, ps, other]
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Title: Intertwined Order in Fractional Chern Insulators from Finite-Momentum Pairing of Composite FermionsComments: 15 pages, 11 figures. v2: updated references and acknowledgmentsSubjects: Strongly Correlated Electrons (cond-mat.str-el)
We investigate the problem of intertwined orders in fractional Chern insulators by considering lattice fractional quantum Hall (FQH) states arising from pairing of composite fermions in the square-lattice Hofstadter model. At certain filling fractions, magnetic translation symmetry ensures the composite fermions form Fermi surfaces with multiple pockets, leading to the formation of finite-momentum Cooper pairs in the presence of attractive interactions. We obtain mean-field phase diagrams exhibiting a rich array of striped and topological phases, establishing paired lattice FQH states as an ideal platform to investigate the intertwining of topological and conventional broken symmetry order.
- arXiv:2003.04328 [pdf, other]
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Title: Bulk Anyons as Edge Symmetries: Boundary Phase Diagrams of Topologically Ordered StatesComments: 33 page, 13 figuresSubjects: Strongly Correlated Electrons (cond-mat.str-el); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Statistical Mechanics (cond-mat.stat-mech); High Energy Physics - Theory (hep-th)
We study quasi-1d systems that emerge at the edge of a topologically ordered state, or at the boundary between two topologically ordered states. We argue that anyons of the bulk are associated with emergent symmetries of the quasi-1d system, which play a crucial role in the structure of its phase diagram. Using this symmetry principle, anyon condensation transitions at the boundaries of Abelian states can be understood in terms of symmetry breaking or symmetry protected topological transitions. Yet more exotic phenomena occur when the bulk hosts non-Abelian anyons. To demonstrate these principles, we explore the phase diagrams of the edges of a single and a double layer of the toric code, as well as those of domain walls in a single and double-layer Kitaev spin liquid (KSL). In the case of the KSL, we find that the presence of a non-Abelian anyon in the bulk enforces Kramers-Wannier self-duality as a symmetry of the effective boundary theory. These examples illustrate a number of surprising phenomena, such as spontaneous duality-breaking, two-sector phase transitions, and unfreezing of marginal operators at a transition between different gapless phases.
- arXiv:2003.04332 [pdf, ps, other]
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Title: Classifying nearest-neighbour interactions and deformations of AdSComments: 6 pagesSubjects: High Energy Physics - Theory (hep-th); Statistical Mechanics (cond-mat.stat-mech); Mathematical Physics (math-ph); Exactly Solvable and Integrable Systems (nlin.SI)
We classify all regular solutions of the Yang-Baxter equation of eight-vertex type. Regular solutions correspond to spin chains with nearest-neighbour interactions. We find a total of four independent solutions. Two are related to the usual six- and eight-vertex models that have R-matrices of difference form. We find two completely new solutions of the Yang-Baxter equation, which are manifestly of non-difference form. These new solutions contain the S-matrices of the AdS2 and AdS3 integrable models as a special case. Consequently, we can classify all possible integrable deformations of eight-vertex type of these holographic integrable systems.
- arXiv:2003.04341 [pdf, other]
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Title: Predicted strong coupling of solid-state spins via a single magnon modeSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Quantum Physics (quant-ph)
We propose an approach to realize a hybrid quantum system composed of a diamond nitrogen-vacancy (NV) center spin coupled to a magnon mode of the low-damping, low-moment organic ferrimagnet vanadium tetracyanoethylene. We derive an analytical expression for the spin-magnon cooperativity as a function of NV position under a micron-scale perpendicularly magnetized disk, and show that, surprisingly, the cooperativity will be higher using this magnetic material than in more conventional materials with larger magnetic moments, due to in part to the reduced demagnetization field. For reasonable experimental parameters, we predict that the spin-magnon-mode coupling strength is $g\sim 10$ kHz. For isotopically pure $^{12}$C diamond we predict strong coupling of an NV spin to the unoccupied magnon mode, with cooperativity $\mathcal C=6$ for a wide range of NV spin locations within the diamond, well within the spatial precision of NV center implantation. Thus our proposal describes a practical pathway for single-spin-state-to-single-magnon-occupancy transduction and for entangling NV centers over micron length scales.
- arXiv:2003.04347 [pdf, other]
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Title: Growth Kinetics and Aging Phenomena in a Frustrated SystemSubjects: Statistical Mechanics (cond-mat.stat-mech); Computational Physics (physics.comp-ph)
We study numerically the ordering kinetics in a two-dimensional Ising model with random coupling where the fraction of antiferromagnetic links $a$ can be gradually tuned. We show that, upon increasing such fraction, the behavior changes in a radical way. Small $a$ does not prevent the system from a complete ordering, but this occurs in an extremely (logarithmically) slow manner. However, larger values of this parameter destroy complete ordering, due to frustration, and the evolution is comparatively faster (algebraic). Our study shows a precise correspondence between the kind of developing order, ferromagnetic versus frustrated, and the speed of evolution. The aging properties of the system are studied by focusing on the scaling properties of two-time quantities, the autocorrelation and linear response functions. We find that the contribution of equilibrium and an aging part to these functions occurs differently in the various regions of the phase diagram of the model. When quenching inside the ferromagnetic phase, the two-time quantities are obtained by the addition of these parts. Instead, in the paramagnetic phase, these two contributions enter multiplicatively. Both of the scaling forms are shown with excellent accuracy, and the corresponding scaling functions and exponents have been determined and discussed.
- arXiv:2003.04349 [pdf, other]
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Title: Toward a 3d Ising model with a weakly-coupled string theory dualComments: 34 pages + appendices. Many plots and pictures of cubes. Appendix E can be cut out and assembled. Code available at this https URLSubjects: High Energy Physics - Theory (hep-th); Statistical Mechanics (cond-mat.stat-mech); Strongly Correlated Electrons (cond-mat.str-el)
It has long been expected that the 3d Ising model can be thought of as a string theory, where one interprets the domain walls that separate up spins from down spins as two-dimensional string worldsheets. The usual Ising Hamiltonian measures the area of these domain walls. This theory has string coupling of unit magnitude. We add new local terms to the Ising Hamiltonian that further weight each spin configuration by a factor depending on the genus of the corresponding domain wall, resulting in a new 3d Ising model that has a tunable bare string coupling $g_s$. We use a combination of analytical and numerical methods to analyze the phase structure of this model as $g_s$ is varied. We study statistical properties of the topology of worldsheets and discuss the prospects of using this new deformation at weak string coupling to find a worldsheet description of the 3d Ising transition.
- arXiv:2003.04351 [pdf, ps, other]
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Title: Rényi and Tsallis entropies of the Dirichlet and Neumann one-dimensional quantum wellsAuthors: O. OlendskiComments: 7 figuresJournal-ref: Int. J. Quantum Chem. vol. 120, e26220 (2020)Subjects: Quantum Physics (quant-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Data Analysis, Statistics and Probability (physics.data-an)
A comparative analysis of the Dirichlet and Neumann boundary conditions (BCs) of the one-dimensional (1D) quantum well extracts similarities and differences of the R\'{e}nyi $R(\alpha)$ as well as Tsallis $T(\alpha)$ entropies between these two geometries. It is shown, in particular, that for either BC the dependencies of the R\'{e}nyi position components on the parameter $\alpha$ are the same for all orbitals but the lowest Neumann one for which the corresponding functional $R$ is not influenced by the variation of $\alpha$. Lower limit $\alpha_{TH}$ of the semi infinite range of the dimensionless R\'{e}nyi/Tsallis coefficient where {\em momentum} entropies exist crucially depends on the {\em position} BC and is equal to one quarter for the Dirichlet requirement and one half for the Neumann one. At $\alpha$ approaching this critical value, the corresponding momentum functionals do diverge. The gap between the thresholds $\alpha_{TH}$ of the two BCs causes different behavior of the R\'{e}nyi uncertainty relations as functions of $\alpha$. For both configurations, the lowest-energy level at $\alpha=1/2$ does saturate either type of the entropic inequality thus confirming an earlier surmise about it. It is also conjectured that the threshold $\alpha_{TH}$ of one half is characteristic of any 1D non-Dirichlet system. Other properties are discussed and analyzed from the mathematical and physical points of view.
- arXiv:2003.04357 [pdf, ps, other]
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Title: Recent progress on superconductors with time-reversal symmetry breakingAuthors: Sudeep Kumar Ghosh, Michael Smidman, Tian Shang, James F. Annett, Adrian Hillier, Jorge Quintanilla, Huiqiu YuanComments: 29 pages, 10 figuresSubjects: Superconductivity (cond-mat.supr-con); Strongly Correlated Electrons (cond-mat.str-el)
Superconductivity and magnetism are antagonistic states of matter. The presence of spontaneous magnetic fields inside the superconducting state is, therefore, an intriguing phenomenon prompting extensive experimental and theoretical research. In this review, we discuss recent experimental discoveries of unconventional superconductors which spontaneously break time-reversal symmetry and theoretical efforts in understanding their properties. We discuss the main experimental probes and give an extensive account of theoretical approaches to understand the order parameter symmetries and the corresponding pairing mechanisms including the importance of multiple bands.
- arXiv:2003.04362 [pdf, other]
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Title: Monte Carlo study of the tip region of branching random walks evolved to large timesComments: 20 pages, 10 figures. v2: discussion of the unconditioned case in Sec. 3 improved, conclusions unchangedSubjects: Statistical Mechanics (cond-mat.stat-mech); High Energy Physics - Phenomenology (hep-ph)
We implement a discretization of the one-dimensional branching Brownian motion in the form of a Monte Carlo event generator, designed to efficiently produce ensembles of realizations in which the rightmost lead particle at the final time $T$ is constrained to have a position $X$ larger than some predefined value $X_{\text{min}}$. The latter may be chosen arbitrarily far from the expectation value of $X$, and the evolution time after which observables on the particle density near the lead particle are measured may be as large as $T\sim 10^4$. We then calculate numerically the probability distribution $p_n(\Delta x)$ of the number $n$ of particles in the interval $[X-\Delta x,X]$ as a function of $\Delta x$. When $X_{\text{min}}$ is significantly smaller than the expectation value of the position of the rightmost lead particle, i.e. when $X$ is effectively unconstrained, we check that both the mean and the typical values of $n$ grow exponentially with $\Delta x$, up to a linear prefactor and to finite-$T$ corrections. When $X_{\text{min}}$ is picked far ahead of the latter but within a region extending over a size of order $\sqrt{T}$ to its right, the mean value of the particle number still grows exponentially with $\Delta x$, but its typical value is lower by a multiplicative factor consistent with $e^{-\zeta\Delta x^{2/3}}$, where $\zeta$ is a number of order unity. These numerical results bring strong support to recent analytical calculations and conjectures in the infinite-time limit.
- arXiv:2003.04366 [pdf, other]
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Title: Bogoliubov Quasiparticles in Superconducting QubitsComments: 47 pages, 14 figures. Lecture notes for the Les Houches summer school on Quantum Information Machines, feedback welcomeSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Superconductivity (cond-mat.supr-con); Quantum Physics (quant-ph)
Extending the qubit coherence times is a crucial task in building quantum information processing devices. In the three-dimensional cavity implementations of circuit QED, the coherence of superconducting qubits was improved dramatically due to cutting the losses associated with the photon emission. Next frontier in improving the coherence includes the mitigation of the adverse effects of superconducting quasiparticles. In these lectures, we review the basics of the quasiparticles dynamics, their interaction with the qubit degree of freedom, their contribution to the qubit relaxation rates, and approaches to control their effect.
- arXiv:2003.04368 [pdf, other]
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Title: Lifshitz transition and frustration of magnetic moments in infinite-layer NdNiO$_2$ upon hole-dopingComments: 6 pages, 6 figuresJournal-ref: Phys. Rev. B 101, 241108(R) (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el); Materials Science (cond-mat.mtrl-sci)
Motivated by the recent discovery of superconductivity in the infinite-layer (Sr,Nd)NiO$_2$ films with Sr content $x \simeq0.2$ [Li et al., Nature (London) \textbf{572}, 624 (2019)], we examine the effects of electron correlations and Sr-doping on the electronic structure, Fermi surface topology, and magnetic correlations in (Nd,Sr)NiO$_2$ using a combination of dynamical mean-field theory of correlated electrons and band-structure methods. Our results reveal a remarkable orbital selective renormalization of the Ni $3d$ bands, with $m$*/$m\sim 3$ and 1.3 for the $d_{x^2-y^2}$ and $d_{3z^2-r^2}$ orbitals, respectively, that suggests orbital-dependent localization of the Ni $3d$ states. We find that upon hole doping (Nd,Sr)NiO$_2$ undergoes a Lifshitz transition of the Fermi surface which is accompanied by a change of magnetic correlations from the three-dimensional (3D) N\'eel $G$-type (111) to the quasi-2D $C$-type (110). We show that magnetic interactions in (Nd,Sr)NiO$_2$ demonstrate an unanticipated frustration, which suppresses magnetic order, implying the importance of in-plane spin fluctuations to explain its superconductivity. Our results suggest that frustration is maximal for Sr-doping $x \simeq 0.1$--0.2, which is in agreement with an experimentally observed doping value Sr $x \simeq 0.2$ of superconducting (Nd,Sr)NiO$_2$.
- arXiv:2003.04395 [pdf, other]
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Title: Shapiro Steps and Nonlinear Skyrmion Hall Angles For dc and ac Driven Skyrmions on a Two Dimensional Periodic SubstrateComments: 15 pages, 26 figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Soft Condensed Matter (cond-mat.soft)
For an overdamped particle moving over a two-dimensional periodic substrate under combined dc and ac drives, a series of steps can appear in the velocity force curves that are known as Shapiro steps. Here we show that for skyrmions driven over a two-dimensional periodic obstacle array with a dc drive and an ac drive that is either parallel or perpendicular to the dc drive, the system exhibits numerous transverse and longitudinal synchronization dynamics due to the Magnus force. These phenomena originate in interactions between two different types of phase locking effects: Shapiro steps and directional locking. In some cases, the skyrmion Hall angle is constant but longitudinal Shapiro steps appear, while in other regimes the skyrmion Hall angle can either increase or decrease with increasing dc drive during the phase locking as the skyrmion locks to different symmetry directions of the obstacle lattice. For a transverse ac drive we find that strong Hall angle overshoots can occur in certain locked phases where the skyrmion is moving at an angle that is considerably larger than the intrinsic Hall angle. For the strongest Magnus force, the phase locking effects are reduced and there are larger regions of disordered dynamics. We show that the skyrmion Hall angle can be controlled by fixing the dc drive and changing the amplitude of the ac drive.
- arXiv:2003.04402 [pdf, other]
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Title: Towards a soft magnetoelastic twist actuatorComments: 13 pages, 14 figuresSubjects: Soft Condensed Matter (cond-mat.soft); Materials Science (cond-mat.mtrl-sci)
Soft actuators allow to transform external stimuli to mechanical deformations. Because of their deformational response to external magnetic fields, magnetic gels and elastomers represent ideal candidates for such tasks. Mostly, linear magnetostrictive deformations, that is, elongations or contractions along straight axes are discussed in this context. In contrast to that, we here suggest to realize a twist actuator that responds by torsional deformations around the axis of the applied magnetic field. For this purpose, we theoretically investigate the overall mechanical response of a basic model system containing discrete magnetizable particles in a soft elastic matrix. Two different types of discrete particle arrangements are used as starting conditions in the nonmagnetized state. These contain globally twisted anisotropic particle arrangements on the one hand, and groups of discrete helical-like particle structures positioned side by side on the other hand. Besides the resulting twist upon magnetization, we also evaluate different other modes of deformation. Our analysis supports the construction of magnetically orientable and actuatable torsional mixing devices in fluidic applications or other types of soft actuators that initiate relative rotations between different components.
- arXiv:2003.04405 [pdf, other]
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Title: The double scaled limit of Super--Symmetric SYK modelsSubjects: High Energy Physics - Theory (hep-th); Statistical Mechanics (cond-mat.stat-mech); Strongly Correlated Electrons (cond-mat.str-el); Mathematical Physics (math-ph); Probability (math.PR)
We compute the exact density of states and 2-point function of the $\mathcal{N} =2$ super-symmetric SYK model in the large $N$ double-scaled limit, by using combinatorial tools that relate the moments of the distribution to sums over oriented chord diagrams. In particular we show how SUSY is realized on the (highly degenerate) Hilbert space of chords. We further calculate analytically the number of ground states of the model in each charge sector at finite $N$, and compare it to the results from the double-scaled limit. Our results reduce to the super-Schwarzian action in the low energy short interaction length limit. They imply that the conformal ansatz of the 2-point function is inconsistent due to the large number of ground states, and we show how to add this contribution. We also discuss the relation of the model to $SL_q(2|1)$. For completeness we present an overview of the $\mathcal{N}=1$ super-symmetric SYK model in the large $N$ double-scaled limit.
- arXiv:2003.04417 [pdf, other]
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Title: Zitterbewegung and Klein-tunneling phenomena for transient quantum wavesComments: Accepted in Phys. Rev. A; 11 pages, 6 figuresJournal-ref: Phys. Rev. A 101, 042104 (2020)Subjects: Quantum Physics (quant-ph); Materials Science (cond-mat.mtrl-sci)
We explore the dynamics of relativistic quantum waves in a potential step by using an exact solution to the Klein-Gordon equation with a point source initial condition. We show that in both the propagation, and Klein-tunneling regimes, the Zitterbewegung effect manifests itself as a series of quantum beats of the particle density in the long-time limit. We demonstrate that the beating phenomenon is characterized by the Zitterbewegung frequency, and that the amplitude of these oscillations decays as $t^{-3/2}$. We show that beating effect also manifests itself in the free Klein-Gordon and Dirac equations within a quantum shutter setup, which involve the dynamics of cut-off quantum states. We also find a time-domain where the particle density of the point source is governed by the propagation of a main wavefront, exhibiting an oscillating pattern similar to the diffraction in time phenomenon observed in non-relativistic systems. The relative positions of these wavefronts are used to investigate the time-delay of quantum waves in the Klein-tunneling regime. We show that, depending on the energy difference, ${\cal E}$, between the source and the potential step, the time-delay can be positive, negative or zero. The latter case corresponds to a super-Klein-tunneling configuration, where ${\cal E}$ equals to half the energy of the potential step.
- arXiv:2003.04437 [pdf, ps, other]
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Title: Why Do Elastin-Like Polypeptides Possibly Have Different Solvation Behaviors in Water-Ethanol and Water-Urea Mixtures?Comments: Accepted for publication in MacromoleculesSubjects: Soft Condensed Matter (cond-mat.soft); Statistical Mechanics (cond-mat.stat-mech)
The solvent quality determines the collapsed or the expanded state of a polymer. For example, a polymer dissolved in a poor solvent collapses, whereas in a good solvent it opens up. While this standard understanding is generally valid, there are examples when a polymer collapses even in a mixture of two good solvents. This phenomenon, commonly known as co-non-solvency, is usually associated with smart polymers. Moreover, recent experiments have shown that the elastin-like polypeptides (ELPs) show co-non-solvency behavior in aqueous-ethanol mixtures. In this study, we investigate the phase behavior of ELPs in aqueous binary mixtures using molecular dynamics simulations of all-atom and complementary explicit solvent generic models. The model is parameterized by mapping the solvation free energy obtained from the all-atom simulations onto the generic interaction parameters. For this purpose, we derive segment based generic parameters for four different peptides, namely proline (P), valine (V), glycine (G) and alanine (A). Here we compare the conformational behavior of two ELP sequences, namely VPGGG and VPGVG, in aqueous-ethanol and -urea mixtures. Consistent with recent experiments, we find that ELPs show co-non-solvency in aqueous-ethanol mixtures. Ethanol molecules have preferential binding with all ELP residues and thus driving the coil-to-globule transition. On the contrary, ELP conformations show weak variation in aqueous-urea mixtures. Our simulations suggest that the glycine residues dictate the overall behavior of ELPs in aqueous-urea, where urea molecules have a rather weak preferential binding with glycine, i.e., less than kT. While the validation of the latter findings will require more detailed experimental investigation, the results presented here may provide a new twist to the present understanding of cosolvent interactions with peptides and proteins.
- arXiv:2003.04440 [pdf, other]
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Title: Ab-Initio self-energy embedding for the photoemission spectra of NiO and MnOComments: 14 pages, 9 figure, 4 tablesSubjects: Strongly Correlated Electrons (cond-mat.str-el); Materials Science (cond-mat.mtrl-sci)
The accurate ab-initio simulation of periodic solids with strong correlations is one of the grand challenges of condensed matter. While mature methods exist for weakly correlated solids, the ab-initio description of strongly correlated systems is an active field of research. In this work, we show results for the single particle spectral function of the two correlated $d$-electron solids NiO and MnO from self-energy embedding theory. Unlike earlier work, the theory does not use any adjustable parameters and is fully ab-initio, while being able to treat both the strong correlation and the non-local screening physics of these materials. We derive the method, discuss aspects of the embedding and choices of physically important orbitals, and compare our results to x-ray and angle-resolved photoemission spectroscopy as well as bremsstrahlung-isochromat spectroscopy.
- arXiv:2003.04446 [pdf, other]
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Title: Nuclear-Electronic All-Particle Density Matrix Renormalization GroupComments: 37 pages, 5 figures, 2 tablesJournal-ref: J. Chem. Phys. 152, 204103 (2020)Subjects: Chemical Physics (physics.chem-ph); Strongly Correlated Electrons (cond-mat.str-el); Computational Physics (physics.comp-ph); Quantum Physics (quant-ph)
We introduce the Nuclear Electronic All-Particle Density Matrix Renormalization Group (NEAP-DMRG) method for solving the time-independent Schr\"odinger equation simultaneously for electrons and other quantum species. In contrast to already existing multicomponent approaches, in this work we construct from the outset a multi-reference trial wave function with stochastically optimized non-orthogonal Gaussian orbitals. By iterative refining of the Gaussians' positions and widths, we obtain a compact multi-reference expansion for the multicomponent wave function. We extend the DMRG algorithm to multicomponent wave functions to take into account inter- and intra-species correlation effects. The efficient parametrization of the total wave function as a matrix product state allows NEAP-DMRG to accurately approximate full configuration interaction energies of molecular systems with more than three nuclei and twelve particles in total, which is currently a major challenge for other multicomponent approaches. We present NEAP-DMRG results for two few-body systems, i.e., H$_2$ and H$_3^+$, and one larger system, namely BH$_3$
- arXiv:2003.04464 [pdf]
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Title: Quantum mechanical current-to-voltage conversion with quantum Hall resistance arraySubjects: Instrumentation and Detectors (physics.ins-det); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Accurate measurement of the electric current requires a stable and calculable resistor for an ideal current to voltage conversion. However, the temporal resistance drift of a physical resistor is unavoidable, unlike the quantum Hall resistance directly linked to the Planck constant h and the elementary charge e. Lack of an invariant high resistance leads to a challenge in making small current measurements below 1 muA with an uncertainty better than one part in 106. In this work, we demonstrate a current to voltage conversion in the range from a few nano amps to one microamp with an invariant quantized Hall array resistance. The converted voltage is directly compared with the Josephson voltage reference in the framework of Ohm's law. Markedly distinct from the classical conversion, which relies on an artifact resistance reference, this current-to-voltage conversion does not demand timely resistance calibrations. It improves the precision of current measurement down to 8 10 -8 at 1 muA.
- arXiv:2003.04467 [pdf]
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Title: Realization of 5 h/e^2 with graphene quantum Hall resistance arraySubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We report on realization of 10 quantum Hall devices in series fabricated using epitaxial graphene on silicon carbide. Precision measurements with a resistance bridge indicates that the quantized Hall resistance across an array at filling factor 2 is equivalent to 5 h/e^2 within the measurement uncertainty of approximately 4 10-8. A quantum-Hall phase diagram for the array shows that a metrological quantization of 5 h/e^2 can be achieved at the magnetic field of 6 T and temperature of 4 K. This experiment demonstrates the possibility of timely unchangeable resistance reference in various ranges in relaxed experimental conditions.
- arXiv:2003.04472 [pdf, other]
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Title: Entanglements and correlations of one-dimensional quantum spin-1/2 chain with anisotropic power-law long range interactionsComments: 8 pages, 9 figuresSubjects: Strongly Correlated Electrons (cond-mat.str-el)
The correlations, entanglement entropy, and fidelity susceptibility are calculated for a one-dimensional spin-1/2 XXZ chain with anisotropic power-law long range interactions by employing the density matrix renormalization group method. In particular, this long-range interaction is assigned to ferromagnetic for transversal components, while it can be either ferro- or antiferromagnetic for the longitudinal spin component. Two ground-state phase diagrams are established versus the anisotropy of the interactions which not only changes the phase boundaries of the counterparts with short-range interactions, but also leads to the emergence of exotic phases. We found that the long-range interactions of the z-component results in a Wigner crystal phase, whereas the transversal one may break a continuous symmetry, resulting in a continuous symmetry breaking phase.
- arXiv:2003.04476 [pdf]
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Title: Resolving pseudosymmetry in tetragonal ZrO2 using EBSD with a modified dictionary indexing approachSubjects: Materials Science (cond-mat.mtrl-sci); Computational Physics (physics.comp-ph)
Resolving pseudosymmetry has long presented a challenge for electron backscatter diffraction (EBSD) and has been notoriously challenging in the case of tetragonal ZrO2 in particular. In this work, a method is proposed to resolve pseudosymmetry by building upon the dictionary indexing method and augmenting it with the application of global optimization to fit accurate pattern centers, clustering of the Hough-indexed orientations to focus the dictionary in orientation space, and interpolation to improve the accuracy of the indexed solution. The proposed method is demonstrated to resolve pseudosymmetry with 100% accuracy in simulated patterns of tetragonal ZrO2, even with high degrees of binning and noise. The method is then used to index an experimental dataset, which confirms its ability to efficiently and accurately resolve pseudosymmetry in these materials. The present method can be applied to resolve pseudosymmetry in a wide range of materials, possibly even some more challenging than tetragonal ZrO2. Source code for this implementation is available online.
- arXiv:2003.04487 [pdf, other]
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Title: Transparent Gatable Superconducting Shadow JunctionsAuthors: Sabbir A. Khan, Charalampos Lampadaris, Ajuan Cui, Lukas Stampfer, Yu Liu, S. J. Pauka, Martin E. Cachaza, Elisabetta M. Fiordaliso, Jung-Hyun Kang, Svetlana Korneychuk, Timo Mutas, Joachim E. Sestoft, Filip Krizek, Rawa Tanta, M. C. Cassidy, Thomas S. Jespersen, Peter KrogstrupComments: 10 pages, 5 figures, 48 referencesSubjects: Materials Science (cond-mat.mtrl-sci); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Superconductivity (cond-mat.supr-con); Applied Physics (physics.app-ph); Quantum Physics (quant-ph)
Gate tunable junctions are key elements in quantum devices based on hybrid semiconductor-superconductor materials. They serve multiple purposes ranging from tunnel spectroscopy probes to voltage-controlled qubit operations in gatemon and topological qubits. Common to all is that junction transparency plays a critical role. In this study, we grow single crystalline InAs, InSb and $\mathrm{InAs_{1-x}Sb_x}$ nanowires with epitaxial superconductors and in-situ shadowed junctions in a single-step molecular beam epitaxy process. We investigate correlations between fabrication parameters, junction morphologies, and electronic transport properties of the junctions and show that the examined in-situ shadowed junctions are of significantly higher quality than the etched junctions. By varying the edge sharpness of the shadow junctions we show that the sharpest edges yield the highest junction transparency for all three examined semiconductors. Further, critical supercurrent measurements reveal an extraordinarily high $I_\mathrm{C} R_\mathrm{N}$, close to the KO$-$2 limit. This study demonstrates a promising engineering path towards reliable gate-tunable superconducting qubits.
- arXiv:2003.04499 [pdf, ps, other]
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Title: Double Andreev reflections and double normal reflections in nodal-line semimetal-superconductor junctionsJournal-ref: Physical Review B 101, 094508 (2020)Subjects: Superconductivity (cond-mat.supr-con)
We study systematically the scattering processes and the conductance spectra in nodal-line semimetalsuperconductor junctions using the extended Blonder-Tinkham-Klapwijk theory. The coexistence of peculiar quadruple reflections are found, which are the specular normal reflection, the retro-normal reflection, the specular Andreev reflection and the retro-Andreev reflection. The incident angle dependence and the quasiparticle energy dependence of the double normal reflections and the double Andreev reflections are investigated under various values of parameters such as the interfacial barrier height, the chemical potentials, and the orbital coupling strength. It is found that the appearance and the disappearance of the reflections and their magnitudes can be controlled through tuning these parameters. The scattering mechanism for the reflections are analyzed in details from the viewpoint of the band structure. We also investigate the conductance spectra for the junctions, which show distinctive features and strong anisotropy about the orientation relationships of the nodal line and interface. The unique scattering processes and conductance spectra found in the junctions are helpful in designing superconducting electronic devices and searching for the nodal line in materials experimentally.
- arXiv:2003.04501 [pdf]
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Title: Experimental observations indicating the topological nature of the edge states on HfTe5Authors: Rui-Zhe Liu, Xiong Huang, Ling-Xiao Zhao, Li-Min Liu, Jia-Xin Yin, Rui Wu, Gen-Fu Chen, Zi-Qiang Wang, Shuheng H. PanJournal-ref: Chin. Phys. Lett. 36, 117301 (2019)Subjects: Materials Science (cond-mat.mtrl-sci); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
The topological edge states of two-dimensional topological insulators with large energy gap furnish ideal conduction channels for dissipationless current transport. Transition metal tellurides XTe5 (X=Zr, Hf) are theoretically predicted to be large-gap two-dimensional topological insulators and the experimental observations of their bulk insulating gap and in-gap edge states have been reported, but the topological nature of these edge states still remains to be further elucidated. Here, we report our low temperature scanning tunneling microscopy/spectroscopy study on single crystals of HfTe5. We demonstrate a full energy gap of ~80 meV near the Fermi level on the surface monolayer of HfTe5 and that such insulating energy gap gets filled with finite energy states when measured at the monolayer step edges. Remarkably, such states are absent at the edges of a narrow monolayer strip of one-unit-cell in width but persist at both step edges of a unit-cell wide monolayer groove. These experimental observations strongly indicate that the edge states of HfTe5 monolayers are not trivially caused by translational symmetry breaking, instead they are topological in nature protected by the 2D nontrivial bulk properties.
- arXiv:2003.04515 [pdf, other]
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Title: Structural Relaxation Time and Dynamic Shear Modulus of Glassy GrapheneComments: 7 pages, 4 figures, accepted for publication on Journal of Non-Crystalline Solids 2020Subjects: Soft Condensed Matter (cond-mat.soft)
We theoretically investigate glass transition behaviors of the glassy graphene in a wide range of temperature, where this amorphous graphene is described as a hard-sphere fluid. The dynamic arrest of a particle is assumingly caused by interactions with its nearest neighbors and surrounding fluid particles. The assumption allows us to analyze roles of local and collective particle mobility. We calculate the temperature dependence of structural relaxation time and dynamic shear modulus, the dynamic fragility, and the glass transition temperature. In addition, correlations between these physical quantities are comprehensively discussed. Our theoretical calculations agree quantitatively well with recent simulations and Dyre's shoving model.
- arXiv:2003.04516 [pdf, other]
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Title: Quantum Many-Body Scar States in Two-Dimensional Rydberg Atom ArraysComments: 10 pages, 5 figuresSubjects: Quantum Gases (cond-mat.quant-gas); Statistical Mechanics (cond-mat.stat-mech); Quantum Physics (quant-ph)
We find exponentially many exact quantum many-body scar states in a two-dimensional PXP model --- an effective model for a two-dimensional Rydberg atom array in the nearest-neighbor blockade regime. Such scar states are remarkably simple valence bond solids despite being at effectively infinite temperature, and thus strongly violate the eigenstate thermalization hypothesis. Given a particular boundary condition, such eigenstates have integer-valued energies. Moreover, certain charge-density-wave initial states give rise to strong oscillations in the Rydberg excitation density after a quantum quench and tower-like structures in their overlaps with eigenstates.
- arXiv:2003.04519 [pdf]
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Title: Approaching Three-Dimensional Quantum Hall effect in Bulk HfTe5Authors: Pang Wang, Yafei Ren, Fangdong Tang, Peipei Wang, Tao Hou, Hualing Zeng, Liyuan Zhang, Zhenhua QiaoSubjects: Materials Science (cond-mat.mtrl-sci)
The discovery of quantum Hall effect in two-dimensional (2D) electronic systems inspired the topological classifications of electronic systems1,2. By stacking 2D quantum Hall effects with interlayer coupling much weaker than the Landau level spacing, quasi-2D quantum Hall effects have been experimentally observed3~7, due to the similar physical origin of the 2D counterpart. Recently, in a real 3D electronic gas system where the interlayer coupling is much stronger than the Landau level spacing, 3D quantum Hall effect has been observed in ZrTe58. In this Letter, we report the electronic transport features of its sister bulk material, i.e., HfTe5, under external magnetic field. We observe a series of plateaus in Hall resistance \r{ho}xy as magnetic field increases until it reaches the quantum limit at 1~2 Tesla. At the plateau regions, the longitudinal resistance \r{ho}xx exhibits local minima. Although \r{ho}xx is still nonzero, its value becomes much smaller than \r{ho}xy at the last few plateaus. By mapping the Fermi surface via measuring the Shubonikov-de Haas oscillation, we find that the strength of Hall plateau is proportional to the Fermi wavelength, suggesting that its formation may be attributed to the gap opening from the interaction driven Fermi surface instability. By comparing the bulk band structures of ZrTe5 and HfTe5, we find that there exists an extra pocket near the Fermi level of HfTe5, which may lead to the finite but nonzero longitudinal conductance.
- arXiv:2003.04539 [pdf]
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Title: Atomic line defects and zero-energy end states in monolayer Fe(Te,Se) high-temperature superconductorsComments: The final version of the manuscript can be found in Nature PhysicsSubjects: Superconductivity (cond-mat.supr-con); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci)
Majorana zero-energy bound states (ZEBSs) have been proposed to exist at the ends of one-dimensional Rashba nanowires proximity-coupled to an s-wave superconductor in an external magnetic field induced Zeeman field. Such hybrid structures have been a central platform in the search for non-Abelian Majorana zero modes (MZMs) toward fault-tolerant topological quantum computing. Here we report the discovery of ZEBSs simultaneously appearing at each end of a one-dimensional atomic line defect in monolayer iron-based high-temperature superconductor FeTe0.5Se0.5 films grown on SrTiO3(001) substrates. The spectroscopic properties of the ZEBSs, including the temperature and tunneling barrier dependences, as well as their fusion induced by coupling on line defects of different lengths are found to be robust and consistent with those of the MZMs. These observations suggest a realization of topological Shockley defects at the ends of an atomic line defect in a two-dimensional s-wave superconductor that can host a Kramers pair of MZMs protected by time-reversal symmetry along the chain. Our findings reveal an unprecedented class of topological line defect excitations in two-dimensional superconductor FeTe0.5Se0.5 monolayer films and offer an advantageous platform for generating topological zero-energy excitations at higher operating temperatures, in a single material, and under zero external magnetic field.
- arXiv:2003.04542 [pdf, ps, other]
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Title: On the quantum correlations in two-qubit XYZ spin chains with Dzyaloshinsky-Moriya and Kaplan-Shekhtman-Entin-Wohlman-Aharony interactionsAuthors: M. A. YurischevComments: 18 pages, no figuresSubjects: Quantum Physics (quant-ph); Statistical Mechanics (cond-mat.stat-mech)
The anisotropic Heisenberg two-spin-1/2 model in an inhomogeneous magnetic field with both antisymmetric Dzyaloshinsky-Moriya and symmetric Kaplan-Shekhtman-Entin-Wohlman-Aharony cross interactions is considered at thermal equilibrium. Using a group-theoretical approach, we find fifteen spin Hamiltonians and as many corresponding Gibbs density matrices (quantum states) whose eigenvalues are expressed only through square radicals. We also found local unitary transformations that connect nine of this fifteen state collection, and one of them is the X quantum state. Since such quantum correlations as quantum entanglement, quantum discord, one-way quantum work deficit, and others are known for the X state, this allows to get the quantum correlations for any member from the nine state family. Further, we show that the remaining six quantum states are separable, that they are also connected by local unitary transformations, but, however, now the case with known correlations beyond entanglement is generally not available.
- arXiv:2003.04543 [pdf, other]
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Title: Mass-zero constrained molecular dynamics for electrode charges in simulations of electrochemical systemsAuthors: Alessandro Coretti, Laura Scalfi, Camille Bacon, Benjamin Rotenberg, Rodolphe Vuilleumier, Giovanni Ciccotti, Mathieu Salanne, Sara BonellaSubjects: Statistical Mechanics (cond-mat.stat-mech); Chemical Physics (physics.chem-ph); Computational Physics (physics.comp-ph)
Classical molecular dynamics simulations have recently become a standard tool for the study of electrochemical systems. State-of-the-art approaches represent the electrodes as perfect conductors, modelling their responses to the charge distribution of electrolytes via the so-called fluctuating charge model. These fluctuating charges are additional degrees of freedom that, in a Born-Oppenheimer spirit, adapt instantaneously to changes in the environment to keep each electrode at a constant potential. Here we show that this model can be treated in the framework of constrained molecular dynamics, leading to a symplectic and time-reversible algorithm for the evolution of all the degrees of freedom of the system. The computational cost and the accuracy of the new method are similar to current alternative implementations of the model. The advantage lies in the accuracy and long term stability guaranteed by the formal properties of the algorithm and in the possibility to systematically introduce additional kinematic conditions of arbitrary number and form. We illustrate the performance of the constrained dynamics approach by enforcing the electroneutrality of the electrodes in a simple capacitor consisting of two graphite electrodes separated by a slab of liquid water.
- arXiv:2003.04550 [pdf]
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Title: A Sampling Strategy in Efficient Potential Energy Surface Mapping for Predicting Atomic Diffusivity in Crystals by Machine LearningSubjects: Materials Science (cond-mat.mtrl-sci)
We propose a machine-learning-based (ML-based) method for efficiently predicting atomic diffusivity in crystals, in which the potential energy surface (PES) of a diffusion carrier is partially evaluated by first-principles calculations. To preferentially evaluate the region of interest governing the atomic diffusivity, a statistical PES model based on a Gaussian process (GP-PES) is constructed and updated iteratively from known information on already-computed potential energies (PEs). In the proposed method, all local energy minima (stable & metastable sites) and elementary processes of atomic diffusion (atomic jumps) are explored on the predictive mean of the GP-PES. The uncertainty of jump frequency in each elementary process is then estimated on the basis of the variance of the GP-PES. The acquisition function determining the next grid point to be computed is designed to reflect the impacts of the uncertainties of jump frequencies on the uncertainty of the macroscopic atomic diffusivity. The numerical solution of the master equation is here employed to readily estimate the atomic diffusivity, which enables us to design the acquisition function reflecting the centrality of each elementary process.
- arXiv:2003.04552 [pdf, other]
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Title: Spontaneous emission of a quantum emitter near a Chern insulator: interplay of time reversal symmetry breaking and van Hove singularityComments: 23 pages, 11 figuresJournal-ref: Phys. Rev. B 101, 205410 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci); Atomic Physics (physics.atom-ph); Optics (physics.optics)
We consider the generic problem of a two-level quantum emitter near a two-dimensional Chern insulator in the dipole approximation, and study how the frequency-dependent response and electronic density of states of the insulator modifies the transition rate of the emitter between the ground and excited levels. To this end, we obtain the full real-frequency behavior of the conductivity tensor by performing a tight-binding calculation based on the Qi-Wu-Zhang model and using a Kubo formula, and derive the full electromagnetic Green tensor of the system, which breaks Onsager reciprocity. This enables us to find that for frequencies smaller than the maximum band gap, the system is sensitive to time reversal symmetry-breaking, whereas for much larger frequencies the system becomes insensitive, with implications for the discrimination of the state of a circularly polarised dipole emitter. We also study the impact of a van Hove singularity on the surface-induced correction to the transition rate, finding that it can enhance its amplitude by a few orders of magnitude compared to the case where the conductivity is set to its static value. By considering configurations in which the dipole is circularly polarised or parallel with the surface of the Chern insulator, we find that the surface correction to the transition rate can exhibit a novel decay with sine integral-like oscillations.
- arXiv:2003.04559 [pdf]
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Title: Concentration-control in all-solution processed semiconducting polymer doping and high conductivity performancesJournal-ref: Synthetic Metals, Volume 262, April 2020, 116352Subjects: Materials Science (cond-mat.mtrl-sci)
Simultaneously optimizing performances, processability and fabrication cost of organic electronic materials is the continual source of compromise hindering the development of disruptive applications. In this work, we identified a strategy to achieve record conductivity values of one of the most benchmarked semiconducting polymers by doping with an entirely solution-processed, water-free and cost-effective technique. High electrical conductivity for poly(3-hexylthiophene) up to 21 S/cm has been achieved, using a commercially available electron acceptor as both a Lewis acid and an oxidizing agent. While we managed water-free solution-processing a three-time higher conductivity for P3HT with a very affordable/available chemical, near-field microscopy reveals the existence of concentration-dependent higher-conductivity micro-domains for which furthermore process optimization might access to even higher performances. In the perpetual quest of reaching higher performances for organic electronics, this work shall greatly unlock applications maturation requiring higher-scale processability and lower fabrication costs concomitant of higher performances and new functionalities, in the current context where understanding the doping mechanism of such class of materials remains of the greatest interest.
- arXiv:2003.04561 [pdf]
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Title: Intrinsic Valley Polarization and Anomalous Valley Hall Effect in Single-Layer 2H-FeCl2Subjects: Materials Science (cond-mat.mtrl-sci)
Valley, as a new degree of freedom for electrons, has drawn considerable attention due to its significant potential for encoding and storing information. Lifting the energy degeneracy to achieve valley polarization is necessary for realizing valleytronic devices. Here, on the basis of first-principles calculations, we show that single-layer FeCl2 exhibits a large spontaneous valley polarization (~101 meV) arising from the broken time-reversal symmetry and spin-orbital coupling, which can be continuously tuned by varying the direction of magnetic crystalline. By employing the perturbation theory, the underlying physical mechanism is unveiled. Moreover, the coupling between valley degree of freedom and ferromagnetic order could generate a spin- and valley-polarized anomalous Hall current in the presence of the in-plane electric field, facilitating its experimental exploration and practical applications.
- arXiv:2003.04562 [pdf]
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Title: Conversion of a conventional superconductor into a topological superconductor by topological proximity effectAuthors: C. X. Trang, N. Shimamura, K. Nakayama, S. Souma, K. Sugawara, I. Watanabe, K. Yamauchi, T. Oguchi, K. Segawa, T. Takahashi, Yoichi Ando, T. SatoComments: 22 pages, 7 figuresJournal-ref: Nat. Commun. 11, 159 (2020)Subjects: Superconductivity (cond-mat.supr-con); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Realization of topological superconductors (TSCs) hosting Majorana fermions is a central challenge in condensed-matter physics. One approach is to use the superconducting proximity effect (SPE) in heterostructures, where a topological insulator contacted with a superconductor hosts an effective p-wave pairing by the penetration of Cooper pairs across the interface. However, this approach suffers a difficulty in accessing the topological interface buried deep beneath the surface. Here, we propose an alternative approach to realize topological superconductivity without SPE. In a Pb(111) thin film grown on TlBiSe2, we discover that the Dirac-cone state of substrate TlBiSe2 migrates to the top surface of Pb film and obtains an energy gap below the superconducting transition temperature of Pb. This suggests that a BCS superconductor is converted into a TSC by the topological proximity effect. Our discovery opens a route to manipulate topological superconducting properties of materials.
- arXiv:2003.04564 [pdf, other]
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Title: A hybrid model for estimation of pore size from ortho-positronium lifetimes in porous materialsAuthors: L. Anh Tuyen, T. Dong Xuan, H. A. Tuan Kiet, L. Chi Cuong, P. Trong Phuc, T. Duy Tap, Van-Phuc Dinh, L. Ly Nguyen, N. T. Ngoc Hue, P. Thi Hue, L. Thai Son, D. Van Hoang, N. Hoang Long, N. Quang HungComments: 18 pages, 4 figures, accepted in Radiation Physics and ChemistrySubjects: Materials Science (cond-mat.mtrl-sci); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
The present paper proposes a novel model for estimating the free-volume size of porous materials based on the analysis of various experimental ortho-positronium ($o$-Ps) lifetime data. The model is derived by combining the semi-classical (SE) physics model, which works in the region of large pores (pore size $R >$ 1 nm), with the conventional Tao-Eldrup (TE) model, which is applicable only for the small-pore region ($R <$ 1 nm). Thus, the proposed model, called the hybrid (HYB) model, is able to smoothly connect the $o$-Ps lifetimes in the two regions of the pore. Moreover, by introducing the $o$-Ps diffusion probability parameter ($D$), the HYB model has reproduced quite well the experimental $o$-Ps lifetimes in the whole region of pore sizes. It is even in a better agreement with the experimental data than the most up-to-date rectangular TE (RTE) and Tokyo models. In particular, by adjusting the value of $D$, the HYB model can also describe very well the two defined sets of experimental $o$-Ps lifetimes in the pores with spherical and channel geometries. The merit of the present model, in comparison with the previously proposed ones, is that it is applicable for the pore size in the universal range of $0.2 - 400$ nm for most of porous materials with different geometries.
- arXiv:2003.04589 [pdf, ps, other]
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Title: Nonadiabatic particle and energy pump at strong system-reservoir couplingComments: 9 pages, 9 figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Statistical Mechanics (cond-mat.stat-mech)
We study the dynamics of electron and energy currents in a nonadiabatic pump. The pump is a quantum dot nanojunction with time-varying gate potential and tunnel couplings to the leads. The leads are unbiased and maintained at the same temperature and chemical potential. We find that synchronized variations of the gate and tunnel couplings can pump electrons and energy from the left to the right lead. Inspired by quantum heat engines, we devise a four-stroke operating protocol that can optimally pump energy and hence, we investigate energy transfer and the coefficient of performance of the device. We compare our device to a two-stroke pump and find that the latter's lower performance is due to the bi-directional flow of energy currents resulting in low net energy currents. The performance of our four-stroke pump can be improved, up to a point, by increasing the net energy carried by the pumped electrons through energy charging via the gate potential. This is achieved by increasing the durations of energy charging and discharging strokes in the pump's protocol. However, despite the large energy output for long charging and discharging strokes, the energy required to maintain the strokes become large too resulting in a stagnant pump performance. Our pump operates effectively only in the strong lead coupling regime and becomes a dud in the weak coupling regime due to the net output energy flowing in the reverse direction. We use nonequilibirum Green's functions techniques to calculate the currents and capture the effects of strong lead-channel coupling exactly while simultaneously incorporating three time-varying parameters. Results from our work could aid in the design of high-performance quantum pumps.
- arXiv:2003.04594 [pdf]
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Title: Collective Transport of Magnetic Microparticles at a Fluid Interface through Dynamic Self-Assembled LatticesSubjects: Soft Condensed Matter (cond-mat.soft)
The transport of motile entities across modulated energy landscapes plays an important role in a range of phenomena in biology, colloidal science and solid-state physics. Here, an easily implementable strategy that allows for the collective and monitored transport of microparticles at fluid-fluid interfaces is introduced. Adsorbed magnetic microparticles are carried on time-dependent magnetic potentials, generated by a dynamic self-assembled lattice of different-sized magnetic particles. In such binary systems, the sudden reorientation of the applied field triggers the rapid exchange between attractive and repulsive configurations, enabling for the ballistic transfer of the carriers through the lattice. As the number of motile entities increases, the induced current increases, before reaching a maximum, while the loaded interface gradually displays bidirectional transport. The described methodology can be tuned through the applied field and exploited for the monitored guidance of adsorbed molecules on liquid surfaces, the segregation of colloidal mixtures, the induced motion of defects in photonic crystals or the design of new self-assembled microrobots.
- arXiv:2003.04608 [pdf]
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Title: Room-temperature ferrimagnetism of anti-site-disordered Ca2MnOsO6Authors: Hai L. Feng, Madhav Prasad Ghimire, Zhiwei Hu, Sheng-Chieh Liao, Stefano Agrestini, Jie Chen, Yahua Yuan, Yoshitaka Matsushita, Yoshihiro Tsujimoto, Yoshio Katsuya, Masahiko Tanaka, Hong-Ji Lin, Chien-Te Chen, Shih-Chang Weng, Manuel Valvidares, Kai Chen, Francois Baudelet, Arata Tanaka, Martha Greenblatt, Liu Hao Tjeng, Kazunari YamauraSubjects: Strongly Correlated Electrons (cond-mat.str-el); Materials Science (cond-mat.mtrl-sci)
Room-temperature ferrimagnetism was discovered for the anti-site-disordered perovskite Ca2MnOsO6 with Tc = 305 K. Ca2MnOsO6 crystallizes into an orthorhombic structure with a space group of Pnma, in which Mn and Os share the oxygen-coordinated-octahedral site at an equal ratio without a noticeable ordered arrangement. The material is electrically semiconducting with variable-range-hopping behavior. X-ray absorption spectroscopy confirmed the trivalent state of the Mn and the pentavalent state of the Os. X-ray magnetic circular dichroism spectroscopy reveals that the Mn and Os magnetic moments are aligned antiferromagnetically, thereby classifying the material as a ferrimagnet which is in accordance with band structure calculations. It is intriguing that the magnetic signal of the Os is very weak, and that the observed total magnetic moment is primarily due to the Mn. The Tc = 305 K is the second highest in the material category of so-called disordered ferromagnets such as CaRu1-xMnxO3, SrRu1-xCrxO3, and CaIr1-xMnxO3, and hence, may support the development of spintronic oxides with relaxed requirements concerning the anti-site disorder of the magnetic ions.
- arXiv:2003.04612 [pdf, other]
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Title: Bandgap engineering in an epitaxial two-dimensional honeycomb Si$_{6-x}$Ge$_x$ alloyAuthors: Antoine Fleurence, Yuto Awatani, Camille Huet, Frank B. Wiggers, Steaphan M. Wallace, Takahiro Yonezawa, Yukiko Yamada-TakamuraSubjects: Materials Science (cond-mat.mtrl-sci)
In this Letter, we demonstrate that it is possible to form a two-dimensional (2D) silicene-like Si$_5$Ge compound by replacing the Si atoms occupying on-top sites in the planar-like structure of epitaxial silicene on ZrB$_2$(0001) by deposited Ge atoms. For coverages below 1/6 ML, the Ge deposition gives rise to a Si$_{6-x}$Ge$_{x}$ alloy (with $x$ between 0 and 1) in which the on-top sites are randomly occupied by Si or Ge atoms. The progressive increase of the valence band maximum with $x$ observed experimentally originates from a selective charge transfer from Ge atoms to Si atoms. These achievements provide evidence for the possibility of engineering the bandgap in 2D SiGe alloys in a way that is similar for their bulk counterpart.
- arXiv:2003.04621 [pdf, ps, other]
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Title: Massively parallel simulations for disordered systemsComments: accepted for publication in EPJB, Topical issue - Recent advances in the theory of disordered systemsSubjects: Computational Physics (physics.comp-ph); Disordered Systems and Neural Networks (cond-mat.dis-nn); Statistical Mechanics (cond-mat.stat-mech)
Simulations of systems with quenched disorder are extremely demanding, suffering from the combined effect of slow relaxation and the need of performing the disorder average. As a consequence, new algorithms, improved implementations, and alternative and even purpose-built hardware are often instrumental for conducting meaningful studies of such systems. The ensuing demands regarding hardware availability and code complexity are substantial and sometimes prohibitive. We demonstrate how with a moderate coding effort leaving the overall structure of the simulation code unaltered as compared to a CPU implementation, very significant speed-ups can be achieved from a parallel code on GPU by mainly exploiting the trivial parallelism of the disorder samples and the near-trivial parallelism of the parallel tempering replicas. A combination of this massively parallel implementation with a careful choice of the temperature protocol for parallel tempering as well as efficient cluster updates allows us to equilibrate comparatively large systems with moderate computational resources.
- arXiv:2003.04622 [pdf, other]
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Title: State-of-the-art and prospects for intense red radiation from core-shell InGaN/GaN nanorodsAuthors: E. A. Evropeitsev (1), D. R. Kazanov (1), Y. Robin (2), A. N. Smirnov (1), I. A. Eliseyev (1), V. Yu. Davydov (1), A. A. Toropov (1), S. Nitta (2), T. V. Shubina (1), H. Amano (2) ((1) Ioffe Institute, (2) Institute of Materials and Systems for Sustainability (IMaSS))Comments: 11 pages, 7 figuresSubjects: Materials Science (cond-mat.mtrl-sci); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Core-shell nanorods (NRs) with InGaN/GaN quantum wells (QWs) are promising for monolithic white light-emitting diodes and multicolor displays. Such applications, however, are still a challenge because intensity of red band is too weak as compared with blue and green ones. To clarify the problem, we have performed power and temperature dependent, as well as time-resolved measurements of photoluminescence (PL) in NRs of different In content and diameter. These studies have shown that the dominant PL bands originate from nonpolar and semipolar QWs, while a broad yellow-red band arises mostly from defects in the GaN core. Intensity of red emission from the polar QWs at the NR tip is fatally small. Our calculation of electromagnetic field distribution inside the NRs shows a low density of photon states in the tip that suppresses the red radiation. We suggest a design of hybrid NRs, in which polar QWs, located inside the GaN core, are pumped by UV-blue radiation of nonpolar QWs. Possibilities of radiative recombination rate enhancement by means of the Purcell effect are discussed.
- arXiv:2003.04632 [pdf, other]
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Title: Multi-scale structural complexity of natural patternsComments: 7 pages, 7 figures; comments are welcome!Subjects: Pattern Formation and Solitons (nlin.PS); Disordered Systems and Neural Networks (cond-mat.dis-nn); Statistical Mechanics (cond-mat.stat-mech)
Complexity of patterns is a key information for human brain to differ objects of about the same size and shape. Like other innate human senses, the complexity perception cannot be easily quantified. We propose a transparent and universal machine method for estimating structural (effective) complexity of two- and three-dimensional patterns that can be straightforwardly generalized onto other classes of objects. It is based on multistep renormalization of the pattern of interest and computing the overlap between neighboring renormalized layers. This way, we can define a single number characterizing the structural complexity of an object. We apply this definition to quantify complexity of various magnetic patterns and demonstrate that not only does it reflect the intuitive feeling of what is ``complex'' and what is ``simple'', but also can be used to accurately detect different phase transitions. When employed for that, the proposed scheme is much simpler and numerically cheaper than the standard methods based on computing correlation functions or using machine learning techniques.
- arXiv:2003.04637 [pdf, other]
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Title: Nanotechnological Structure for Observation of Current Induced Contact Potential Difference and Creation of Effective Cooper Pair Mass-SpectroscopyComments: 10+4 pages (1 appendix), 4 figures, 35 referencesSubjects: Superconductivity (cond-mat.supr-con)
Changes of the electron work-function of a superconductor proportional to the square of the current density $\Delta \phi = -\beta j^2$ are known as Bernoulli effect in superconductors or current induced Contact Potential Difference (CPD). The temperature dependent constant $\beta(T;m^{\star})$ is parametrized by the effective mass of Cooper pairs $m^{\star}$. In such a way the study of the Bernoulli effect leads to creation of Cooper pair mass-spectroscopy. In this paper a short review on the Bernoulli effect in superconductors is given and a proposed experimental set-up for its measurement is described in detail. The experiment requires standard electronic equipment and can be implemented in every laboratory related to physics of superconductivity. This experimental set-up for observation of current induced CPD requires nano-technological hybrid superconductor structures with atomically clean interfaces and measurement of nano-volt signals with capacitive coupling to the sample.
- arXiv:2003.04659 [pdf, other]
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Title: Mediated interactions and photon bound states in an exciton-polariton mixtureComments: 9 pages, 4 figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Quantum Gases (cond-mat.quant-gas); Quantum Physics (quant-ph)
The quest to realise strongly interacting photons remains an outstanding challenge both for fundamental science and for applications. Here, we explore mediated photon-photon interactions in a highly imbalanced two-component mixture of exciton-polaritons in a semiconductor microcavity. Using a theory that takes into account non-perturbative correlations between the excitons as well as strong light-matter coupling, we demonstrate the high tunability of an effective interaction between quasiparticles formed by minority component polaritons interacting with a Bose-Einstein condensate (BEC) of a majority component polaritons. In particular, the interaction, which is mediated by the exchange of sound modes in the BEC can be made strong enough to support a bound state of two quasiparticles. Since these quasiparticles consist partly of photons, this in turn corresponds to a dimer state of photons propagating through the BEC. This gives rise to a new light transmission line where the bound state wave function is directly mapped onto correlations between outgoing photons. Our findings open up new routes for realising highly non-linear optical materials and novel hybrid light-matter quantum systems.
- arXiv:2003.04670 [pdf, other]
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Title: Symmetry resolved entanglement entropy of excited states in a CFTSubjects: Statistical Mechanics (cond-mat.stat-mech)
We report a throughout analysis of the entanglement entropies related to different symmetry sectors in the low-lying primary excited states of a conformal field theory (CFT) with an internal U(1) symmetry. Our findings extend recent results for the ground state. We derive a general expression for the charged moments, i.e. the generalised cumulant generating function, which can be written in terms of correlation functions of the operator that define the state through the CFT operator-state correspondence. We provide explicit analytic computations for the compact boson CFT (aka Luttinger liquid) for the vertex and derivative excitations. The Fourier transform of the charged moments gives the desired symmetry resolved entropies. At the leading order, they satisfy entanglement equipartition, as in the ground state, but we find, within CFT, subleading terms that break it. Our analytical findings are checked against free fermions calculations on a lattice, finding excellent agreement. As a byproduct, we have exact results for the full counting statistics of the U(1) charge in the considered excited states.
- arXiv:2003.04673 [pdf]
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Title: Exciton-Exciton Interaction and Cascade Relaxation of Excitons in Colloidal CdSe NanoplateletsAuthors: Aleksandr M. Smirnov, Anastasiya D. Golinskaya, Bedil M. Saidzhonov, Vladimir N. Mantsevich, Vladimir S. Dneprovskii, Roman B. VasilievSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Optics (physics.optics)
We experimentally investigated for the first time the lowest four band structure of Cd Se nanoplatelets at the r point of Brillouin zone [heavy-hole (hh), light-hole (lh) and two spin-orbital bands] and its modification due to the changing of the CdS shell thickness. The results of an experimental and theoretical study of exciton dynamics in colloidal CdSe/CdS nanoplateles are presented in the case of stationary laser excitation. The excitation was performed by means of the powerful nanosecond laser and the pump and probe technique was utilized. The differential transmission spectra peculiarities
- arXiv:2003.04680 [pdf, other]
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Title: Dzyaloshinskii-Moriya interaction in absence of spin-orbit couplingAuthors: Ramon Cardias, Anders Bergman, Attila Szilva, Yaroslav O. Kvashnin, Jonas Fransson, Angela B. Klautau, Olle Eriksson, Lars NordströmSubjects: Materials Science (cond-mat.mtrl-sci)
In contrast to conventional assumptions, we show that the Dzyaloshinskii-Moriya interaction can be of non-relativistic origin, in particular in materials with a non-collinear magnetic configuration, where non-relativistic contributions can dominate over spin-orbit effects. The weak antiferromagnetic phase of Mn$_{3}$Sn is used to illustrate these findings. Using electronic structure theory as a conceptual platform, all relevant exchange interactions are derived for a general, non-collinear magnetic state. It is demonstrated that non-collinearity influences all three types of exchange interaction and that physically distinct mechanisms, which connect to electron- and spin-density and currents, may be used as a general way to analyze and understand magnetic interactions of the solid state.
- arXiv:2003.04681 [pdf, ps, other]
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Title: Dynamical Localization and Delocalization in Polychromatically Perturbed Anderson MapComments: 12 pages, 15 figuresSubjects: Disordered Systems and Neural Networks (cond-mat.dis-nn)
In the previous paper[arXiv:1911.02189], localization and delocalization phenomena in the polychromatically perturbed Anderson map (AM) were elucidated mainly from the viewpoint of localization-delocalization transition (LDT) on the increasing of the perturbation strength $\epsilon$. In this paper, we mainly investigate the disorder strength $W-$dependence of the phenomena in the AM with a characetristic disorder strength $W^*$. In the completely localized region the $W-$dependence and $\epsilon-$dependence of the localization length show characteristic behavior similar to those reported in monochromatically perturbed case [PRE 97,012210(2018)]. Furthermore, the obtained results show that even for the increase of the $W$, the critical phenomena and critical exponent are found to be similar to those in the LDT caused by the increase of $\epsilon$. We also investigate the diffusive properties of the delocalized states induced by the parameters.
- arXiv:2003.04682 [pdf, other]
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Title: Multiple insulating phases due to the interplay of strong correlations and lattice geometry in a single-orbital Hubbard modelSubjects: Strongly Correlated Electrons (cond-mat.str-el)
We find ten distinct ground states for the single-orbital Hubbard model on the decorated honeycomb lattice, which interpolates between the honeycomb and kagome lattices, and is the simplest two-dimensional net. The rich phase diagram includes a real-space Mott insulator, dimer and trimer Mott insulators, a spin triplet Mott insulator, flat band ferromagnets, and Dirac metals. It is determined as a function of interaction strength, band filling, and hopping anisotropy, using rotationally invariant slave boson mean-field theory.
- arXiv:2003.04683 [pdf, other]
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Title: To Measure, or Not to Measure, That is the QuestionComments: 11 pages, 7 figures, comments are welcomeSubjects: Statistical Mechanics (cond-mat.stat-mech); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Quantum Physics (quant-ph)
A method is proposed that allows one to infer the sum of the values of an observable taken during contacts with a pointer state. Hereby the state of the pointer is updated while contacted with the system and remains unchanged between contacts while the system evolves in time. After a prescribed number of such contacts the position of the pointer is determined by means of a projective measurement. The outcome is specified in terms of a probability distribution function for unitary and Markovian dissipative dynamics and compared with the results of the same number of generalized Gaussian measurements of the considered observable. As a particular example a qubit is considered with an observable contacting to the pointer that does not commute with the system Hamiltonian.
- arXiv:2003.04689 [pdf, other]
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Title: Adaptive phase field modelling of crack propagation in orthotropic functionally graded materialsJournal-ref: Defence Technology (2020)Subjects: Computational Engineering, Finance, and Science (cs.CE); Materials Science (cond-mat.mtrl-sci); Numerical Analysis (math.NA)
In this work, we extend the recently proposed adaptive phase field method to model fracture in orthotropic functionally graded materials (FGMs). A recovery type error indicator combined with quadtree decomposition is employed for adaptive mesh refinement. The proposed approach is capable of capturing the fracture process with a localized mesh refinement that provides notable gains in computational efficiency. The implementation is validated against experimental data and other numerical experiments on orthotropic materials with different material orientations. The results reveal an increase in the stiffness and the maximum force with increasing material orientation angle. The study is then extended to the analysis of orthotropic FGMs. It is observed that, if the gradation in fracture properties is neglected, the material gradient plays a secondary role, with the fracture behaviour being dominated by the orthotropy of the material. However, when the toughness increases along the crack propagation path, a substantial gain in fracture resistance is observed.
- arXiv:2003.04702 [pdf, other]
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Title: Equilibration of quantum cat statesAuthors: Tony JinComments: 19 pages, 3 figuresSubjects: Quantum Physics (quant-ph); Statistical Mechanics (cond-mat.stat-mech); Mathematical Physics (math-ph)
We study the equilibration properties of isolated ergodic quantum systems initially prepared in a cat state, i.e a macroscopic quantum superposition of states. Our main result consists in showing that, even though decoherence is at work in the mean, there exists a remnant of the initial quantum coherences visible in the strength of the fluctuations of the steady state. We back-up our analysis with numerical results obtained on the XXX spin chain with a random field along the z-axis in the ergodic regime and find good qualitative and quantitative agreement with the theory. We also present and discuss a framework where equilibrium quantities can be computed from general statistical ensembles without relying on microscopic details about the initial state, akin to the eigenstate thermalization hypothesis.
- arXiv:2003.04704 [pdf]
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Title: CdO/MgO superlattices grown by MBE as cubic CdMgO quasi-alloysAuthors: E. Przezdziecka1, A. Wierzbicka1, P. Dluzewski1, I. Sankowska2, K. Morawiec1, M.A. Pietrzyk1, A. Kozanecki1Subjects: Materials Science (cond-mat.mtrl-sci)
New perspective cubic quasi-alloys CdO/MgO short period superlattices were grown on sapphire substrates by plasma assisted molecular beam epitaxy. Their crystal quality was characterized using High Resolution X-ray Diffraction (HRXRD) and Transmission Electron Microscopy (TEM) techniques. The thickness and growth rate of MgO and CdO individual layers have been extracted. Small angle X-ray diffraction peaks corresponding to the period of the superlattices ranging from 0.6 to 5 nm were clearly observed. From the XRD measurements we obtain 65% relaxation to the substrate of superlattice (SL) in Sample A (CdO/MgO - 4.7 nm/1 nm) and 96% relaxation of SL in Sample B (CdO/MgO - 2 nm/4 nm). Surface roughness parameters for SL were obtained both by Small angle X-ray diffraction and Atomic Force Microcopy studies.
- arXiv:2003.04711 [pdf]
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Title: Physics for Neuromorphic ComputingSubjects: Emerging Technologies (cs.ET); Applied Physics (physics.app-ph)
Neuromorphic computing takes inspiration from the brain to create energy efficient hardware for information processing, capable of highly sophisticated tasks. In this article, we make the case that building this new hardware necessitates reinventing electronics. We show that research in physics and material science will be key to create artificial nano-neurons and synapses, to connect them together in huge numbers, to organize them in complex systems, and to compute with them efficiently. We describe how some researchers choose to take inspiration from artificial intelligence to move forward in this direction, whereas others prefer taking inspiration from neuroscience, and we highlight recent striking results obtained with these two approaches. Finally, we discuss the challenges and perspectives in neuromorphic physics, which include developing the algorithms and the hardware hand in hand, making significant advances with small toy systems, as well as building large scale networks.
- arXiv:2003.04722 [pdf, other]
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Title: Structure and rheology of suspensions of spherical strain-hardening capsulesSubjects: Fluid Dynamics (physics.flu-dyn); Soft Condensed Matter (cond-mat.soft); Computational Physics (physics.comp-ph)
We investigate the rheology of strain-hardening spherical capsules, from the dilute to the concentrated regime under a confined shear flow using three-dimensional numerical simulations. We consider the effect of capillary number, volume fraction and membrane inextensibility on the particle deformation and on the effective suspension viscosity and normal stress differences of the suspension. The suspension displays a shear-thinning behaviour which is a characteristic of soft particles such as emulsion droplets, vesicles, strain-softening capsules, and red blood cells. We find that the membrane inextensibility plays a significant role on the rheology and can almost suppress the shear-thinning. For concentrated suspensions a non-monotonic dependence of the normal stress differences on the membrane inextensibility is observed, reflecting a similar behaviour in the particle shape. The effective suspension viscosity, instead, grows and eventually saturates, for very large inextensibilities, approaching the solid particle limit. In essence, our results reveal that strain-hardening capsules share rheological features with both soft and solid particles depending on the ratio of the area dilatation to shear elastic modulus. Furthermore, the suspension viscosity exhibits a universal behaviour for the parameter space defined by the capillary number and the membrane inextensibility, when introducing the particle geometrical changes at the steady-state in the definition of the volume fraction.
- arXiv:2003.04741 [pdf, other]
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Title: Persistence of hierarchical network organization and emergent topologies in models of functional connectivityComments: 4 figuresSubjects: Disordered Systems and Neural Networks (cond-mat.dis-nn); Physics and Society (physics.soc-ph); Neurons and Cognition (q-bio.NC)
Functional networks provide a topological description of activity patterns in the brain, as they stem from the propagation of activity on the anatomical, or structural network of synaptic connections, which possess a hierarchical organization. While it is assumed that structural networks shape their functional counterparts, it is also hypothesized that alterations of brain activity may come with transformations of functional connectivity, and possibly its deviation from the hierarchical topology. In this computational study, we introduce a novel methodology to monitor the persistence and breakdown of hierarchical order in functional networks, generated from simulations of activity spreading on both synthetic and real structural connectomes. We show that hierarchical connectivity is persistent in the quasi-critical regime associated with optimal processing capabilities and normal brain function (Griffiths phase) and breaks down in states deviating from this regime, often associated with pathological conditions. Our results offer important clues for the study of optimal neurocomputing architectures and processes, which are capable of tuning patterns of activity and information flow, and show how the hierarchical topology and its quasi-critical functional counterpart provide an effective balance between local specialized processing and global integration.
- arXiv:2003.04748 [pdf, ps, other]
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Title: On the coexistence of competing languagesComments: 18 pages, 12 figures, 47 references. To appear in EPJ BJournal-ref: Eur. Phys. J. B (2020) 93, 73Subjects: Statistical Mechanics (cond-mat.stat-mech); Computation and Language (cs.CL)
We investigate the evolution of competing languages, a subject where much previous literature suggests that the outcome is always the domination of one language over all the others. Since coexistence of languages is observed in reality, we here revisit the question of language competition, with an emphasis on uncovering the ways in which coexistence might emerge. We find that this emergence is related to symmetry breaking, and explore two particular scenarios -- the first relating to an imbalance in the population dynamics of language speakers in a single geographical area, and the second to do with spatial heterogeneity, where language preferences are specific to different geographical regions. For each of these, the investigation of paradigmatic situations leads us to a quantitative understanding of the conditions leading to language coexistence. We also obtain predictions of the number of surviving languages as a function of various model parameters.
- arXiv:2003.04790 [pdf]
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Title: Mechanisms of surface nanostructuring of Al2O3 and MgO by grazing incidence irradiation with swift heavy ionsAuthors: Marko Karlusic, Ruslan A. Rymzhanov, Jacques H. O'Connell, Lara Brockers, Kristina Tomic Luketic, Zdravko Siketic, Stjepko Fazinic, Pavo Dubcek, Milko Jaksic, Georgios Provatas, Nikita Medvedev, Alexander E. Volkov, Marika SchlebergerSubjects: Materials Science (cond-mat.mtrl-sci)
We experimentally discovered that Al2O3 and MgO exhibit well-pronounced nanometric modifications on the surfaces when irradiated under grazing incidence with 23 MeV I beam, in contrast to normal incidence irradiation with the same ion beam when no damage was found. Moreover, ions in these two materials produce notably different structures: grooves surrounded with nanohillocks on MgO surfaces vs. smoother, roll-like discontinuous structures on the surfaces of Al2O3. To explain these results, detailed numerical simulations were performed. We identified that a presence of the surface inhibits recrystallization process, thereby preventing transient tracks from recovery, and thus forming observable nanopatterns. Furthermore, a difference in the viscosities in molten states in Al2O3 vs. MgO explains the differences in the created nanostructures. Our results thus provide a deeper understanding of the fundamental processes of surface nanostructuring, potentially allowing for controlled production of periodic surface nanopatterns.
- arXiv:2003.04813 [pdf, other]
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Title: Strain induced magnetic transition in CaMnO$_3$ ultra thin filmsAuthors: A. López Pedroso, M.A. Barral, M.E. Graf, A.M. Llois, M.H. Aguirre, L.B. Steren, S. Di NapoliSubjects: Materials Science (cond-mat.mtrl-sci)
The effect of high tensile strain and low dimensionality on the magnetic and electronic properties of CaMnO$_3$ thin films, epitaxially grown on SrTiO$_3$ substrates, are experimentally studied and theoretically analyzed. The appearance of a ferromagnetic hysteresis loop, absent in the bulk compound due to its G-type antiferromagnetic structure, is observed in the thin films. By means of ab initio calculations, we find that, both, the high strain produced by the substrate and the presence of the free surface contribute to the stabilization of an in-plane ferromagnetic coupling, giving rise to a non-zero net magnetic moment in the thin films. Coupled with this change in the magnetic order we find an insulator-metal transition triggered by the quantum confinement and the tensile epitaxial strain.
- arXiv:2003.04830 [pdf, other]
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Title: Pattern formation in two-dimensional hard-core/soft-shell systems with variable soft shell profilesAuthors: Walter R. C. Somerville, Adam D. Law, Marcel Rey, Nicolas Vogel, Andrew J. Archer, D. Martin A. BuzzaComments: 12 pages, 7 figuresSubjects: Soft Condensed Matter (cond-mat.soft); Statistical Mechanics (cond-mat.stat-mech)
Hard-core/soft shell (HCSS) particles have been shown to self-assemble into a remarkably rich variety of structures under compression due to the simple interplay between the hard-core and soft-shoulder length scales in their interactions. Most studies in this area model the soft shell interaction as a square shoulder potential. Although appealing from a theoretical point of view, the potential is physically unrealistic because there is no repulsive force in the soft shell regime, unlike in experimental HCSS systems. To make the model more realistic, here we consider HCSS particles with a range soft shell potential profiles beyond the standard square shoulder form and study the model using both minimum energy calculations and Monte Carlo simulations. We find that by tuning density and the soft shell profile, HCSS particles in the thin shell regime (i.e., shell to core ratio $r_1/r_0 \leq \sqrt{3}$) can form a large range of structures, including hexagons, chains, squares, rhomboids and two distinct zig-zag structures. Furthermore, by tuning the density and $r_1/r_0$, we find that HCSS particles with experimentally realistic linear ramp soft shoulder repulsions can form honeycombs and quasicrystals with 10-fold and 12-fold symmetry. Our study therefore suggests the exciting possibility of fabricating these exotic 2D structures experimentally through colloidal self-assembly.
- arXiv:2003.04835 [pdf, other]
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Title: Dynamics of a two-dimensional quantum spin-orbital liquid: spectroscopic signatures of fermionic magnonsComments: 6 pages, 2 figuresSubjects: Strongly Correlated Electrons (cond-mat.str-el)
We provide an exact study of dynamical correlations for the quantum spin-orbital liquid phases of an SU(2)-symmetric Kitaev honeycomb lattice model. We show that the spin dynamics in this Kugel-Khomskii type model is exactly the density-density correlation function of $S=1$ fermionic magnons, which could be probed in resonant inelastic x-ray scattering experiments. We also predict the characteristic signatures of spin-orbital fractionalization in inelastic neutron scattering experiments and compare them to the ones of the spin-anisotropic Kitaev honeycomb spin liquid.
- arXiv:2003.04849 [pdf, other]
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Title: Evidence for unbounded growth of the number entropy in many-body localized phasesSubjects: Disordered Systems and Neural Networks (cond-mat.dis-nn); Quantum Gases (cond-mat.quant-gas); Strongly Correlated Electrons (cond-mat.str-el)
We investigate the number entropy $S_N$---which characterizes particle-number fluctuations between subsystems---following a quench in one-dimensional interacting many-body systems with potential disorder. We find evidence that in the regime which is expected to show many-body localization (MBL) and where the entanglement entropy grows as $S\sim \ln t$ as function of time $t$, the number entropy grows as $S_N\sim\ln\ln t$, indicating continuing particle transport at a very slow rate. We demonstrate that this growth is consistent with a relation between entanglement and number entropy recently established for non-interacting systems.
- arXiv:2003.04853 [pdf, other]
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Title: Torsional Anomalies and Bulk-Dislocation Correspondence in Weyl SystemsComments: 16 pagesSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Superconductivity (cond-mat.supr-con); High Energy Physics - Theory (hep-th)
Based on the supersymmetric quantum mechanical approach, we have systematically studied both the $U\left(1\right)$ gauge anomaly and the diffeomorphism anomaly in Weyl systems with torsion, curvature and external electromagnetic fields. These anomalies relate to the chiral current (or current) non-conservation and chiral energy-momentum (or energy-momentum) non-conservation, respectively, which can be applied to the $^{3}\text{He-A}$ phase, the chiral superconductors and the Weyl semimetals with dislocations and disclinations. In sharp difference with other anomalies, there exist torsional anomalies depending on the position of Weyl nodes in the energy-momentum space. These anomalies originate from particles pumped up through the Weyl nodes and they are thus insensitive to the ultra-violet physics, while the Nieh-Yan anomaly is from the particle inflow through the ultra-violet cut-off. The current non-conservation as well as the energy-momentum non-conservation are found, which stem from the zero modes trapped in the dislocations and they can be understood from the Callan-Harvey mechanism. Finally, by comparing our results with the well-established momentum anomaly in the $^{3}\text{He-A}$ phase, the Nieh-Yan term as well as other cut-off dependent terms are shown to be negligible, because the ratio between the Lorentz symmetry breaking scale and the chemical potential is of order $10^{-5}$.
- arXiv:2003.04859 [pdf]
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Title: Scattering matrix of arbitrary tight-binding HamiltoniansComments: 7 figuresJournal-ref: Ann. Phys. 378 (2017) 303-316Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Computational Physics (physics.comp-ph)
A novel efficient method to calculate the scattering matrix (SM) of arbitrary tight-binding Hamiltonians is proposed, including cases with multiterminal structures. In particular, the SM of two kind of fundamental structures are given, which can be used to obtain the SM of bigger systems iteratively. Also, a procedure to obtain the SM of layer-composed periodic leads is described. This method allows renormalization approaches, which permits computations over macroscopic length systems without introducing additional approximations. Finally, the transmission coefficient of a ring-shaped multiterminal system and the transmission function of a square-lattice nanoribbon with a reduced width region are calculated.
- arXiv:2003.04869 [pdf, ps, other]
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Title: Resonance peak shift in the photo-current of ultrahigh-mobility two-dimensional electron systemsAuthors: Jesus InarreaComments: Accepted in Physical Review B 6 pages, 5 figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We report on a theoretical study on the rise of strong peaks at the harmonics of the cyclotron resonance in the irradiated magnetoresistance in ultraclean two-dimensional electron systems. The motivation is the experimental observation of a totally unexpected strong resistance peak showing up at the second harmonic. We extend the radiation-driven electron orbit model (previously developed to study photocurrent oscillations and zero resistance states) to a ultraclean scenario that implies longer scattering time and longer mean free path. Thus, when the mean free path is equivalent, in terms of energy, to twice the cyclotron energy ($2\hbar w_{c}$), the electron behaves as under an effective magnetic field twice the one really applied. Then, at high radiation power and/or low temperature, a resistance spike can be observed {\it at the second harmonic}. For even cleaner samples the energy distance could increase to three or four times the cyclotron energy giving rise to resistance peaks at higher harmonics (third, fourth, etc.), i.e., a resonance peak shift to lower magnetic fields as the quality of the sample increases. Thus, by selecting the sample mobility one automatically would select the radiation resonance response without altering the radiation frequency.
- arXiv:2003.04885 [pdf, other]
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Title: Magnetic flux noise in superconducting qubits and the gap states continuumComments: 7 pages, 2 figuresSubjects: Superconductivity (cond-mat.supr-con)
In the present study we investigate the selected local aspects of the metal-induced gap states (MIGSs) at the disordered metal-insulator interface, that were previously proposed to produce magnetic moments responsible for the magnetic flux noise in some of the superconducting qubit modalities. Our analysis attempts to supplement the available studies and provide new theoretical contribution toward their validation. In particular, we explicitly discuss the behavior of the MIGSs in the momentum space as a function of the local onsite energy deviation, that mimics random potential disorder at the interface. It is found, that when the difference between the characteristic electronic potentials in the insulator increases, the corresponding MIGSs become more localized. This effect is associated with the increasing degree of the potential disorder that was earlier observed to produce highly localized MIGSs in the superconducting qubits. At the same time, the presented findings show that the disorder-induced localization of the MIGSs can be related directly to the decay characteristics of these states as well as to the bulk electronic properties of the insulator. As a result, our study reinforces plausibility of the previous corresponding investigations on the origin of the flux noise, but also allows to draw future directions toward their better verification.
Replacements
- arXiv:1106.3870 (replaced) [pdf, ps, other]
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Title: The origin of phase transitions enlightened by an elementary classical spin modelAuthors: Fabrizio BaroniComments: 8 page, 7 figuresJournal-ref: Eur. Phys. J. B (2020) 93: 45Subjects: Statistical Mechanics (cond-mat.stat-mech)
We introduce a classical spin model with long-range interaction undergoing a first-order $\mathbb{Z}_2$-symmetry breaking phase transition (SBPT) which is in our knowledge one of the simplest models showing such a phenomenon. Its aim is to enlighten the generating-mechanism of a SBPT in general, at least for long-range systems, even though it may be give hints useful also for short-range systems. Further, we present a general rule to model the shape of the long-range potential energy of a Hamiltonian system for a $\mathbb{Z}_2$-SBPT to occur. The main feature is a double-well potential which competes with the concavity of the entropy in shaping the free energy, accordingly to Landau mean-field theory of SBPTs. Finally, we revisit the Ising and the spherical model (Berlin-Kak) models in the mean version at the light of the results obtained here. The model introduced here may be suitable even for didactic purposes and for numerical investigation of the dynamic near the transition point.
- arXiv:1511.02557 (replaced) [pdf, other]
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Title: Linear magnetoresistance induced by intra-scattering semiclassics of Bloch electronsComments: 4 pages, 4 figuresSubjects: Materials Science (cond-mat.mtrl-sci); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
The weak field magnetoresistance has seen a revived interest due to the distinct role played by the momentum-space Berry curvature of Bloch electrons. While most previous studies in this regard focus on the inter-scattering motion of semiclassical Bloch electrons in electromagnetic fields, the intra-scattering effects of the semiclassical dynamics augmented by the Berry curvature, magnetic moment and shift vector on the magnetoresistance have been largely overlooked. Here we uncover that these intra-scattering effects, which are neglected in the field-independent relaxation time approximation to the Boltzmann collision integral, can be as important as the inter-scattering ones. Concrete calculations on the two dimensional gapped Dirac model show that the sign of the negative linear magnetoresistance given by the Berry curvature alone is reversed when one considers the magnetic moment and shift vector.
- arXiv:1803.03977 (replaced) [pdf, other]
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Title: Orbital Fingerprint of Topological Fermi Arcs in a Weyl SemimetalAuthors: Chul-Hee Min, Hendrik Bentmann, Jennifer N. Neu, Philipp Eck, Simon K. Moser, Tim Figgemeier, Maximilian Ünzelmann, Katharina Treiber, Peter Lutz, Roland Koch, Chris Jozwiak, Aaron Bostwick, Eli Rotenberg, Ronny Thomale, Giorgio Sangiovanni, Theo Siegrist, Domenico Di Sante, Friedrich ReinertJournal-ref: Phys. Rev. Lett. 122, 116402 (2019)Subjects: Strongly Correlated Electrons (cond-mat.str-el)
The monopnictides TaAs and TaP are well-established Weyl semimetals. Yet, a precise assignment of Fermi arcs, accomodating the predicted chiral charge of the bulk Weyl points, has been difficult in these systems, and the topological character of different surface features in the Fermi surface is not fully understood. Here, employing a joint analysis from linear dichroism in angle-resolved photoemission and first-principles calculations, we unveil the orbital texture on the full Fermi surface of TaP(001). We observe pronounced switches in the orbital texture at the projectedWeyl nodes, and show how they facilitate a topological classification of the surface band structure. Our findings establish a critical role of the orbital degrees of freedom in mediating the surface-bulk connectivity in Weyl semimetals.
- arXiv:1807.04955 (replaced) [pdf, other]
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Title: Self-learning Monte Carlo method with Behler-Parrinello neural networksComments: 14 pages, 5 figuresJournal-ref: Phys. Rev. B 101, 115111 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el); Computational Physics (physics.comp-ph)
We propose a general way to construct an effective Hamiltonian in the Self-learning Monte Carlo method (SLMC), which speeds up Monte Carlo simulations by training an effective model to propose uncorrelated configurations in the Markov chain. Its applications are, however, limited. This is because it is not obvious to find the explicit form of the effective Hamiltonians. Particularly, it is difficult to make trainable effective Hamiltonians including many-body interactions. In order to overcome this critical difficulty, we introduce the Behler-Parrinello neural networks (BPNNs) as "effective Hamiltonian'' without any prior knowledge, which is used to construct the potential-energy surfaces in interacting many particle systems for molecular dynamics. We combine SLMC with BPNN by focusing on a divisibility of Hamiltonian and propose how to construct the element-wise configurations. We apply it to quantum impurity models. We observed significant improvement of the acceptance ratio from 0.01 (the effective Hamiltonian with the explicit form) to 0.76 (BPNN). This drastic improvement implies that the BPNN effective Hamiltonian includes many body interaction, which is omitted in the effective Hamiltonian with the explicit forms. The BPNNs make SLMC more promising.
- arXiv:1810.10477 (replaced) [pdf]
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Title: Radiation Damage and Thermal Recovery of Perovskite Superconductor Yttrium Barium Copper OxideAuthors: A. Khobnya, M. E. Pek, G. Greaves, M. Danaie, G. D. Brittles, S. E. Donnelly, F. Schoofs, A. Reilly, P. D. Edmondson, S. PedrazziniSubjects: Materials Science (cond-mat.mtrl-sci)
High temperature superconducting materials are being considered to generate the magnetic fields required for the confinement of plasma in fusion reactors. The present study aims to assess the microstructural degradation resulting from ion implantation at room temperature under two implantation conditions in Yttrium Barium Copper Oxide (YBCO) tapes. Xray Diffraction (XRD) and high resolution characterisation techniques including Atom Probe Tomography (APT) and Transmission Electron Microscopy (TEM) analyses were used to correlate alterations in superconducting behaviour measured using a Magnetic Properties Measurement System (MPMS) to amorphization and recovery caused by ion implantation. TEM analysis was performed to depth profile the degree of crystallinity (or lack thereof) on irradiated samples. SRIM predicted the damage depth at 900 nm below the sample surface of the 2 MeV Xe implanted sample and 450 nm beneath the surface of the 0.6 MeV Xe implanted sample. 2 MeV Xe implantation caused the superconducting temperature to decrease by 10 K and the critical current density to display a 10 fold reduction. Post irradiation heat treatments up to 600C caused recrystallisation of the irradiated layer, but also oxygen loss and alterations in grain size. The recrystallised grain orientation was random in TEM lamellae, however, bulk samples re-grew along the original crystal orientation provided that some of the original material was not amorphized (ie if they nucleated on crystalline YBCO). This is extremely promising for the thermal recovery of tokamak components.
- arXiv:1903.04945 (replaced) [pdf, ps, other]
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Title: Partial Isometries, Duality, and Determinantal Point ProcessesComments: v3: AMS-LaTeX, 60 pages, no figure. arXiv admin note: substantial text overlap with arXiv:2002.07760Subjects: Probability (math.PR); Statistical Mechanics (cond-mat.stat-mech); Mathematical Physics (math-ph)
A determinantal point process (DPP) is an ensemble of random nonnegative-integer-valued Radon measures $\Xi$ on a space $S$ with measure $\lambda$, whose correlation functions are all given by determinants specified by an integral kernel $K$ called the correlation kernel. We consider a pair of Hilbert spaces, $H_{\ell}, \ell=1,2$, which are assumed to be realized as $L^2$-spaces, $L^2(S_{\ell}, \lambda_{\ell})$, $\ell=1,2$, and introduce a bounded linear operator ${\cal W} : H_1 \to H_2$ and its adjoint ${\cal W}^{\ast} : H_2 \to H_1$. We show that if ${\cal W}$ is a partial isometry of locally Hilbert--Schmidt class, then we have a unique DPP on $(\Xi_1, K_1, \lambda_1)$ associated with ${\cal W}^* {\cal W}$. In addition, if ${\cal W}^*$ is also of locally Hilbert--Schmidt class, then we have a unique pair of DPPs, $(\Xi_{\ell}, K_{\ell}, \lambda_{\ell})$, $\ell=1,2$. We also give a practical framework which makes ${\cal W}$ and ${\cal W}^{\ast}$ satisfy the above conditions. Our framework to construct pairs of DPPs implies useful duality relations between DPPs making pairs. For a correlation kernel of a given DPP our formula can provide plural different expressions, which reveal different aspects of the DPP. In order to demonstrate these advantages of our framework as well as to show that the class of DPPs obtained by this method is large enough to study universal structures in a variety of DPPs, we report plenty of examples of DPPs in one-, two-, and higher-dimensional spaces $S$, where several types of weak convergence from finite DPPs to infinite DPPs are given. One-parameter ($d \in \mathbb{N}$) series of infinite DPPs on $S=\mathbb{R}^d$ and $\mathbb{C}^d$ are discussed, which we call the Euclidean and the Heisenberg families of DPPs, respectively, following the terminologies of Zelditch.
- arXiv:1904.02717 (replaced) [pdf, other]
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Title: Emergent non-Fermi-liquid phenomena in multipolar quantum impurity systemsComments: Published version: 7 pages, 16 pages Supplementary Information (including references)Journal-ref: Phys. Rev. Research 2, 013257 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el)
Discovery of novel spin-orbital entangled quantum ground states paves an important avenue for controllable quantum materials via unique couplings to the lattice and other external perturbations. In this work, motivated by recent experiments on cubic heavy fermion materials with multipolar local moments, we theoretically investigate strongly-interacting spin-orbital entangled quantum ground states in multipolar quantum impurity systems. Here itinerant electrons are interacting with the local moments carrying quadrupolar and octupolar moments, in contrast to the conventional Kondo problem with dipolar local moment. Using perturbative renormalization group methods, we uncover a number of non-Fermi liquid ground states, which are characterized by an absence of well-defined quasiparticles and singular power-law behaviours in physical properties. We show that the non-Fermi liquid states found here are outside the known categories of non-Fermi liquid states in the conventional multi-channel Kondo problem. This work lays a novel ground for the identification of unexpected non-Fermi liquid phases in many strongly spin-orbital-coupled quantum materials.
- arXiv:1904.03499 (replaced) [pdf, other]
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Title: Entropy production in systems with unidirectional transitionsComments: (Accepted for publication in Physical Review Research)Journal-ref: Phys. Rev. Research 2, 023011 (2020)Subjects: Statistical Mechanics (cond-mat.stat-mech)
The entropy production is one of the most essential features for systems operating out of equilibrium. The formulation for discrete-state systems goes back to the celebrated Schnakenberg's work and hitherto can be carried out when for each transition between two states also the reverse one is allowed. Nevertheless, several physical systems may exhibit a mixture of both unidirectional and bidirectional transitions, and how to properly define the entropy production in this case is still an open question. Here, we present a solution to such a challenging problem. The average entropy production can be consistently defined, employing a mapping that preserves the average fluxes, and its physical interpretation is provided. We describe a class of stochastic systems composed of unidirectional links forming cycles and detailed-balanced bidirectional links, showing that they behave in a pseudo-deterministic fashion. This approach is applied to a system with time-dependent stochastic resetting. Our framework is consistent with thermodynamics and leads to some intriguing observations on the relation between the arrow of time and the average entropy production for resetting events.
- arXiv:1904.08700 (replaced) [pdf, ps, other]
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Title: Asymptotic behavior of correlation functions of one-dimensional polar-molecules on optical latticesAuthors: Theja N. De SilvaComments: Ten pages with five figuresSubjects: Quantum Gases (cond-mat.quant-gas)
We combine a slave-spin approach with a mean-field theory to develop an approximate theoretical scheme to study the density, spin, and, pairing correlation functions of fermionic polar molecules. We model the polar molecules subjected to a one-dimensional periodic optical lattice potential using a generalized $t-J$ model, where the long-range part of the interaction is included through the exchange interaction parameter. For this model, we derive a set of self-consistent equations for the correlation functions, and evaluate them numerically for the long-distance behaviour. We find that the pairing correlations are related to spin correlations through the density and the slave-spin correlations. Further, our calculations indicates that the long-range character of the interaction can be probed through these correlation functions. In the absence of exact solutions for the one-dimensional $t-J$ model, our approximate theoretical treatment can be treated as a useful tool to study one dimensional long-range correlated fermions.
- arXiv:1905.10032 (replaced) [pdf, ps, other]
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Title: Interaction between two modes of field mediated by two quantum dots in a photonic crystal cavitySubjects: Quantum Physics (quant-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We show unusual cooperative two-photon resonance between two-modes of field inside a photonic crystal cavity. The two-photon resonance occurs when two off resonant quantum dots emit one photon in each cavity mode and de-excite simultaneously. In the presence of phonon coupling the conditions for two-photon resonance change significantly. Using such two-photon two-mode interaction we propose to generate entangled state of two qutrits. The basis of a qutrit are formed by the state of the cavity mode containing $0$, $1$ and $2$ photons. We also discuss effect of phonon coupling on negativity of the generated entangled state.
- arXiv:1906.01270 (replaced) [pdf, other]
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Title: Determining the Electron-Phonon Coupling in Superconducting Cuprates by Resonant Inelastic X-ray Scattering: Methods and Results on Nd$_{1+x}$Ba$_{2-x}$Cu$_3$O$_{7-δ}$Authors: Lucio Braicovich, Matteo Rossi, Roberto Fumagalli, Yingying Peng, Yan Wang, Riccardo Arpaia, Davide Betto, Gabriella M. De Luca, Daniele Di Castro, Kurt Kummer, Marco Moretti Sala, Mattia Pagetti, Giuseppe Balestrino, Nicholas B. Brookes, Marco Salluzzo, Steven Johnston, Jeroen van den Brink, Giacomo GhiringhelliComments: 21 pages, 16 figuresSubjects: Superconductivity (cond-mat.supr-con); Strongly Correlated Electrons (cond-mat.str-el)
The coupling between lattice vibration quanta and valence electrons can induce charge density modulations and decisively influence the transport properties of materials, e.g. leading to conventional superconductivity. In high critical temperature superconductors, where electronic correlation is the main actor, the actual role of electron-phonon coupling (EPC) is being intensely debated theoretically and investigated experimentally. We present an in-depth study of how the EPC strength can be obtained directly from resonant inelastic x-ray scattering (RIXS) data through the theoretical approach derived by Ament et al. [EPL 95, 27008 (2011)]. The role of the model parameters (e.g. phonon energy $\omega_0$, intermediate state lifetime $1/\Gamma$, EPC matrix element $M$, and detuning energy $\Omega$) is thoroughly analyzed, providing general relations among them that can be used to make quantitative estimates of the dimensionless EPC $g = (M/\omega_0)^2$ without detailed microscopic modeling. We then apply these methods to very high resolution Cu $L_3$ edge RIXS spectra of three Nd$_{1+x}$Ba$_{2-x}$Cu$_3$O$_{7-\delta}$ films. For the insulating antiferromagnetic parent compound the value of $M$ as a function of the in-plane momentum transfer is obtained for Cu-O bond-stretching (breathing) and bond-bending (buckling) phonon branches. For the underdoped and the nearly optimally doped samples, the effects of Coulomb screening and of charge-density-wave correlations on $M$ are assessed. In light of the anticipated further improvements of the RIXS experimental resolution, this work provides a solid framework for an exhaustive investigation of the EPC in cuprates and other quantum materials.
- arXiv:1906.05398 (replaced) [pdf]
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Title: Self-driving laboratory for accelerated discovery of thin-film materialsAuthors: Benjamin P. MacLeod, Fraser G. L. Parlane, Thomas D. Morrissey, Florian Häse, Loïc M. Roch, Kevan E. Dettelbach, Raphaell Moreira, Lars P. E. Yunker, Michael B. Rooney, Joseph R. Deeth, Veronica Lai, Gordon J. Ng, Henry Situ, Ray H. Zhang, Michael S. Elliott, Ted H. Haley, David J. Dvorak, Alán Aspuru-Guzik, Jason E. Hein, Curtis P. BerlinguetteComments: 43 pages, 9 figuresSubjects: Applied Physics (physics.app-ph); Materials Science (cond-mat.mtrl-sci)
Discovering and optimizing commercially viable materials for clean energy applications typically takes over a decade. Self-driving laboratories that iteratively design, execute, and learn from material science experiments in a fully autonomous loop present an opportunity to accelerate this research. We report here a modular robotic platform driven by a model-based optimization algorithm capable of autonomously optimizing the optical and electronic properties of thin-film materials by modifying the film composition and processing conditions. We demonstrate this platform by using it to maximize the hole mobility of organic hole transport materials commonly used in perovskite solar cells and consumer electronics. This demonstration highlights the possibilities of using autonomous laboratories to discover organic and inorganic materials relevant to materials sciences and clean energy technologies.
- arXiv:1907.00003 (replaced) [pdf, ps, other]
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Title: A charged finitely extensible dumbbell model: Explaining rheology of dilute polyelectrolyte solutionsComments: 36 pages, 8 figuresJournal-ref: Phys. Fluids 32, 063101 (2020)Subjects: Soft Condensed Matter (cond-mat.soft); Fluid Dynamics (physics.flu-dyn)
A robust non-Newtonian fluid model of dilute polyelectrolyte solutions is derived from kinetic theory arguments. Polyelectrolyte molecules are modeled as finitely elongated nonlinear elastic dumbbells, where effective charges (interacting through a simple Coulomb force) are added to the beads in order to model the repulsion between the charged sections of polyelectrolyte chains. It is shown that the relative strength of this repulsion is regulated by the electric-to-elastic energy ratio, $E$, which is one of the key parameters of the model. In particular, $E$ accounts for the intrinsic rigidity of polyelectrolyte molecules and can be used to explain the impact of solvent salinity on polyelectrolyte rheology. With two preaveraging approximations, the constitutive equations of the resulting fluid model are formulated in closed form. Material functions predicted by the model for steady shear flow, steady extensional flow, small-amplitude oscillatory shear flow, and start-up and cessation of steady shear flow are obtained and investigated using a combination of analytical and numerical methods. In particular, it is shown how these material functions depend on $E$. The two limiting cases of the model -- uncharged dumbbells ($E=0$) and rigid dumbbells ($E\to \infty$) -- are included in the analysis. It is found that despite its simplicity, the model predicts most of experimentally observed rheological features of polyelectrolyte solutions.
- arXiv:1908.00959 (replaced) [pdf]
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Title: Quantifying Exchange Forces of a Non-Collinear Magnetic Structure on the Atomic ScaleAuthors: Nadine Hauptmann, Soumyajyoti Haldar, Tzu-Chao Hung, Wouter Jolie, Mara Gutzeit, Daniel Wegner, Stefan Heinze, Alexander A. KhajetooriansSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
The large interest in chiral magnetic structures for realization of nanoscale magnetic storage or logic devices has necessitated methods which can quantify magnetic interactions at the atomic scale. To overcome the limitations of the typically used current-based sensing of atomic-scale exchange interactions, a force-based detection scheme is highly advantageous. Here, we quantify the atomic-scale exchange force field between a ferromagnetic tip and a cycloidal spin spiral using our developed combination of current and exchange force detection. Compared to the surprisingly weak spin polarization, the exchange force field is more sensitive to atomic-scale variations in the magnetization. First-principles calculations reveal that the measured atomic-scale variations in the exchange force originate from different contributions of direct and indirect (Zener) type exchange mechanisms, depending on the chemical tip termination. Our work opens the perspective of quantifying different exchange mechanisms of chiral magnetic structures with atomic-scale precision using 3D magnetic exchange force field measurements.
- arXiv:1908.05044 (replaced) [pdf, other]
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Title: Magnetic hedgehog lattices in noncentrosymmetric metalsComments: 14 pages, 10 figuresJournal-ref: Phys. Rev. B 101, 144416 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el)
The magnetic hedgehog lattice (HL) is a noncoplanar magnetic texture with a periodic array of magnetic monopoles and anti-monopoles. Despite phenomenological and numerical studies thus far, there remain open issues on the microscopic origin, especially with respect to the recent experimental findings of two different types of HLs even at zero magnetic field. Here, we study the stability of the HLs for an effective spin model with long-range interactions arising from itinerant nature of electrons. By variational calculations and simulated annealing, we find that the HLs are stabilized in the ground state at zero magnetic field by the synergetic effect of the anti-symmetric exchange interactions generated by the spin-orbit coupling and the multiple-spin interactions generated by the spin-charge coupling. We also clarify the phase diagram in the magnetic fields, which includes topological phase transitions with pair annihilation of the monopoles and anti-monopoles depending on the field directions.
- arXiv:1908.07958 (replaced) [pdf, other]
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Title: Encoding of Matrix Product States into Quantum Circuits of One- and Two-Qubit GatesAuthors: Shi-Ju RanComments: 7 pages, 5 figuresJournal-ref: Phys. Rev. A 101, 032310 (2020)Subjects: Quantum Physics (quant-ph); Strongly Correlated Electrons (cond-mat.str-el)
The matrix product state (MPS) belongs to the most important mathematical models in, for example, condensed matter physics and quantum information sciences. However, to realize an $N$-qubit MPS with large $N$ and large entanglement on a quantum platform is extremely challenging, since it requires high-level qudits or multi-body gates of two-level qubits to carry the entanglement. In this work, an efficient method that accurately encodes a given MPS into a quantum circuit with only one- and two-qubit gates is proposed. The idea is to construct the unitary matrix product operators that optimally disentangle the MPS to a product state. These matrix product operators form the quantum circuit that evolves a product state to the targeted MPS with a high fidelity. Our benchmark on the ground-state MPS's of the strongly-correlated spin models show that the constructed quantum circuits can encode the MPS's with much fewer qubits than the sizes of the MPS's themselves. This method paves a feasible and efficient path to realizing quantum many-body states and other MPS-based models as quantum circuits on the near-term quantum platforms.
- arXiv:1908.09858 (replaced) [pdf, other]
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Title: Anomalies, a mod 2 index, and dynamics of 2d adjoint QCDComments: Various minor improvements to exposition and clarifications on relations to previous literatureJournal-ref: SciPost Phys. 8, 072 (2020)Subjects: High Energy Physics - Theory (hep-th); Strongly Correlated Electrons (cond-mat.str-el)
We show that $2$d adjoint QCD, an $SU(N)$ gauge theory with one massless adjoint Majorana fermion, has a variety of mixed 't Hooft anomalies. The anomalies are derived using a recent mod $2$ index theorem and its generalization that incorporates 't Hooft flux. Anomaly matching and dynamical considerations are used to determine the ground-state structure of the theory. The anomalies, which are present for most values of $N$, are matched by spontaneous chiral symmetry breaking. We find that massless $2$d adjoint QCD confines for $N >2$, except for test charges of $N$-ality $N/2$, which are deconfined. In other words, $\mathbb Z_N$ center symmetry is unbroken for odd $N$ and spontaneously broken to $\mathbb Z_{N/2}$ for even $N$. All of these results are confirmed by explicit calculations on small $\mathbb{R}\times S^1$. We also show that this non-supersymmetric theory exhibits exact Bose-Fermi degeneracies for all states, including the vacua, when $N$ is even. Furthermore, for most values of $N$, $2$d massive adjoint QCD describes a non-trivial symmetry-protected topological (SPT) phase of matter, including certain cases where the number of interacting Majorana fermions is a multiple of $8$. As a result, it fits into the classification of $(1+1)$d SPT phases of interacting Majorana fermions in an interesting way.
- arXiv:1909.01740 (replaced) [pdf, other]
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Title: Minimax Isometry Method: A compressive sensing approach for Matsubara summation in many-body perturbation theoryComments: 19 pages, 11 figuresSubjects: Materials Science (cond-mat.mtrl-sci); Strongly Correlated Electrons (cond-mat.str-el); Functional Analysis (math.FA); Numerical Analysis (math.NA)
We present a compressive sensing approach for the long standing problem of Matsubara summation in many-body perturbation theory. By constructing low-dimensional, almost isometric subspaces of the Hilbert space we obtain optimum imaginary time and frequency grids that allow for extreme data compression of fermionic and bosonic functions in a broad temperature regime. The method is applied to the random phase and self-consistent $GW$ approximation of the grand potential. Integration and transformation errors are investigated for Si and SrVO$_3$.
- arXiv:1909.03398 (replaced) [pdf]
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Title: Antiadiabatic View of Fast Environmental Effects on Optical SpectraAuthors: D. K. Andrea Phan Huu, Rama Dhali, Carlotta Pieroni, Francesco Di Maiolo, Cristina Sissa, Francesca Terenziani, Anna PainelliComments: 5 pages, 4 figures Plus supporting info (12 pages, 7 fig)Journal-ref: Phys. Rev. Lett. 124, 107401 (2020)Subjects: Materials Science (cond-mat.mtrl-sci); Soft Condensed Matter (cond-mat.soft)
An antiadiabatic approach is proposed to model how the refractive index of the surrounding medium affects optical spectra of molecular systems in condensed phases. The approach solves some of the issues affecting current implementations of continuum solvation models and more generally of effective models where a classical description is adopted for the molecular environment.
- arXiv:1909.03605 (replaced) [pdf]
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Title: Distinguishing between dynamical and static Rashba effects in hybrid perovskite nanocrystals using transient absorption spectroscopyAuthors: Yuri D. Glinka, Rui Cai, Junzi Li, Xiaodong Lin, Bing Xu, Kai Wang, Rui Chen, Tingchao He, Xiao Wei SunComments: Under consideration at Nature CommunicationsSubjects: Applied Physics (physics.app-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
The dynamical and static Rashba effects in hybrid methylammonium (MA) lead halide perovskites have recently been theoretically predicted. However, only the static effect was experimentally confirmed so far. Here we report on the dynamical Rashba effect observed using snapshot transient absorption spectral imaging with 400 nm pumping for a fully encapsulated film of 20-nm-sized 3D MAPbBr3 nanocrystals. The effect causes a 240 meV splitting of the lowest-energy absorption bleaching band, initially appearing over sub-ps timescale and progressively stabilizing to 60 meV during 500 ps. The integrated intensities of the split subbands demonstrate a photon-helicity-dependent asymmetry, thus proving the Rashba-type splitting and providing direct experimental evidence for the Rashba spin-split edge states in lead halide perovskite materials. The ultrafast dynamics is governed by the relaxation of two-photon-excited electrons in the Rashba spin-split system caused by a built-in electric field originating from dynamical charge separation in the entire MAPbBr3 nanocrystal.
- arXiv:1909.04720 (replaced) [pdf, other]
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Title: Intrinsic photon loss at the interface of superconducting devicesComments: 5 pages, 1 figure. Appendix: 6 pages, 1 figureSubjects: Quantum Physics (quant-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We present a quantum theory of dielectric energy loss arising from the piezoelectric coupling between photons and phonons in superconducting devices. Photon loss is shown to occur predominantly at the interface, where the piezoelectric effect is non-zero even when the materials are perfectly crystalline (epitaxial) and free of two-level system defects. We present explicit numerical calculations for the value of the intrinsic loss tangent at several interfaces to conclude that the $T_1$ of superconducting qubits may reach $10^{4}$ $\mu$s if the device is made with defect-free interfaces.
- arXiv:1909.08669 (replaced) [pdf, other]
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Title: Shear-Driven Flow of Athermal, Frictionless, Spherocylinder Suspensions in Two Dimensions: Particle Rotations and Orientational OrderingComments: 29 pages, 41 figures, updated to correspond to published version. Animations included as supplemental material at: this http URLJournal-ref: Phys. Rev. E 101, 032901 (2020)Subjects: Soft Condensed Matter (cond-mat.soft)
We use numerical simulations to study the flow of a bidisperse mixture of athermal, frictionless, soft-core two dimensional spherocylinders driven by a uniform steady-state simple shear applied at a fixed volume and a fixed finite strain rate $\dot\gamma$. Energy dissipation is via a viscous drag with respect to a uniformly sheared host fluid, giving a simple model for flow in a non-Brownian suspension with Newtonian rheology. Considering a range of packing fractions $\phi$ and particle asphericities $\alpha$ at small $\dot\gamma$, we study the angular rotation $\dot\theta_i$ and the nematic orientational ordering $\mathbf{S}_2$ of the particles induced by the shear flow, finding a non-monotonic behavior as the packing $\phi$ is varied. We interpret this non-monotonic behavior as a crossover from a small $\phi$ region where single-particle-like behavior occurs, to a large $\phi$ region where the geometry of the dense packing dominates, the reduced free volume inhibits motion, and a random Poisson-like process for particle rotations results. We also argue that the finite nematic ordering $\mathbf{S}_2$ is a consequence of the shearing serving as an ordering field, rather than a result of long-ranged cooperative behavior among the particles. We arrive at these conclusions by consideration of (i) the distribution of waiting times for a particle to rotate by $\pi$, (ii) the behavior of the system under pure, as compared to simple, shearing, (iii) the relaxation of the nematic order parameter $\mathbf{S}_2$ when perturbed away from the steady state, and (iv) by construction a numerical mean-field model for the rotational motion of a particle. Our results also help to explain the singular behavior observed when taking the $\alpha\to 0$ limit approaching circular disks.
- arXiv:1909.10521 (replaced) [pdf, other]
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Title: Number conserving analysis of measurement-based braiding with Majorana zero modesComments: 8 pages+appendices, 1 figure, v3Journal-ref: Phys. Rev. B 101, 125108 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Strongly Correlated Electrons (cond-mat.str-el); Quantum Physics (quant-ph)
Majorana-based quantum computation seeks to encode information non-locally in pairs of Majorana zero modes, thereby isolating qubit states from a local noisy environment. In addition to long coherence times, the attractiveness of Majorana-based quantum computing relies on achieving topologically protected Clifford gates from braiding operations. Recent works have conjectured that mean-field BCS calculations may fail to account for non-universal corrections to the Majorana braiding operations. Such errors would be detrimental to Majorana-based topological quantum computing schemes. In this work, we develop a particle-number conserving approach for measurement-based topological quantum computing and investigate the effect of quantum phase fluctuations. We demonstrate that braiding transformations are indeed topologically protected in charge-protected Majorana-based quantum computing schemes.
- arXiv:1909.11853 (replaced) [pdf, other]
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Title: "Butterfly Effect" in Shear-Banding Mediated Plasticity of Metallic GlassesAuthors: Baoan Sun, Liping Yu, Gang Wang, Xing Tong, Chuan Geng, Jingtao Wang, Jingli Ren, Weihua WangComments: 12 pages, 5 figuresSubjects: Materials Science (cond-mat.mtrl-sci); Disordered Systems and Neural Networks (cond-mat.dis-nn)
Metallic glasses response to the mechanical stress in a complex and inhomogeneous manner with plastic strain highly localized into nanoscale shear bands. Contrary to the well-defined deformation mechanism in crystalline solids, understanding the mechanical response mechanism and its intrinsic correlation with the macroscopical plasticity in metallic glasses remains long-standing issues. Through a combination of experimental and theoretical analysis, we showed that the shear banding process in metallic glasses exhibits complex chaotic dynamics, which manifests as the existence of a torus destroyed phase diagram, a positive Lyapunov exponent and a fractional Lyapunov dimension. We also demonstrated that the experimentally observed large plasticity fluctuation of metallic glasses tested at the same conditions can be interpreted from the chaotic shear-band dynamics, which could leads to an uncertainty on the appearance of the critical condition for runaway shear banding. Physically, the chaotic shear-band dynamics arises from the interplay between structural disordering and temperature rise within the shear band. By tuning the deformation parameters, the chaotic dynamics can be transformed to a periodic orbit state corresponding to a smaller plasticity fluctuation in metallic glasses. Our results suggest that the plastic flow of metallic glasses is a complex dynamic process, which is highly sensitive to initial conditions and reminiscent of the "butterfly effect" as observed in many complex dynamic systems.
- arXiv:1909.12402 (replaced) [pdf, other]
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Title: Landauer transport as a quasisteady state on finite chains under unitary quantum dynamicsComments: 19 pages, 14 figuresJournal-ref: Phys. Rev. B 101, 104203 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Disordered Systems and Neural Networks (cond-mat.dis-nn)
In this paper, we study the emergence of a Landauer transport regime from the quantum-mechanical dynamics of free electrons in a disordered tight-binding chain, which is coupled to finite leads with open boundaries. Both partitioned and partition-free initial conditions are analyzed and seen to give rise, for large enough leads, to the same spatially uniform quasi-steady-state current, which agrees with the Landauer value. The quasi-steady-state regime is preceded by a transient regime, which last for a time proportional to the length of the disordered sample, and followed by recursions, after a time that is proportional to the lead size. These theoretical predictions may be of interest to future experiments on transport of fermionic ultra-cold atoms across optical lattices. We also observe finite-size current oscillations, superimposed on the quasi-steady-state, whose behavior depends crucially on the conditions initially imposed on the system. Finally, we show how a time-resolved Kubo formula is able to reproduce this Landauer transport regime, as the leads grow bigger.
- arXiv:1910.03073 (replaced) [pdf, other]
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Title: Density-functional model for van der Waals interactions: Unifying many-body atomic approaches with nonlocal functionalsComments: final versionJournal-ref: Phys. Rev. Lett. 124, 146401 (2020)Subjects: Materials Science (cond-mat.mtrl-sci); Chemical Physics (physics.chem-ph)
Noncovalent van der Waals (vdW) interactions are responsible for a wide range of phenomena in matter. Popular density-functional methods that treat vdW interactions use disparate physical models for these intricate forces, and as a result the applicability of these methods is often restricted to a subset of relevant molecules and materials. Aiming towards a general-purpose density functional model of vdW interactions, here we unify two complementary approaches: nonlocal vdW functionals for polarization and interatomic methods for many-body interactions. The developed nonlocal many-body dispersion method (MBD-NL) increases the accuracy and efficiency of existing vdW functionals and is shown to be broadly applicable to molecules, soft and hard materials including ionic and metallic compounds, as well as organic/inorganic interfaces.
- arXiv:1910.09548 (replaced) [pdf, other]
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Title: Complex density wave orders and quantum phase transitions in a model of square-lattice Rydberg atom arraysComments: 7+4 pages, 4+1 figuresJournal-ref: Phys. Rev. Lett. 124, 103601 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el); Quantum Gases (cond-mat.quant-gas); Atomic Physics (physics.atom-ph); Quantum Physics (quant-ph)
We describe the zero-temperature phase diagram of a model of a two-dimensional square-lattice array of neutral atoms, excited into Rydberg states and interacting via strong van der Waals interactions. Using the density-matrix renormalization group algorithm, we map out the phase diagram and obtain a rich variety of phases featuring complex density wave orderings, upon varying lattice spacing and laser detuning. While some of these phases result from the classical optimization of the van der Waals energy, we also find intrinsically quantum-ordered phases stabilized by quantum fluctuations. These phases are surrounded by novel quantum phase transitions, which we analyze by finite-size scaling numerics and Landau theories. Our work highlights Rydberg quantum simulators in higher dimensions as promising platforms to realize exotic many-body phenomena.
- arXiv:1910.10585 (replaced) [pdf, other]
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Title: Boundary-induced effect encoded in the corrections to the geometric phase acquired by a bipartite two-level systemComments: 12 pages, 9 figuresJournal-ref: Phys. Rev. A 101, 032337 (2020)Subjects: Quantum Physics (quant-ph); Other Condensed Matter (cond-mat.other)
We present a bipartite two-level system coupled to electromagnetic quantum vacuum fluctuations through a general dipolar coupling. We derive the master equation in the framework of open quantum systems, assuming an environment composed of (i) solely vacuum fluctuations and (ii) the vacuum fluctuations and a conducting plate located at a fixed distance from the bipartite system. For both cases considered, we study the dynamics of the bipartite system and the temporal evolution of the concurrence of an initial entangled bipartite state. We further analyze the generation of entanglement due to the vacuum structure. Finally, we study the different induced contributions to the correction of the unitary geometric phase of a bipartite quantum state so as to explore the possibility of future experimental setups by considering the influence of boundaries conditions in vacuum
- arXiv:1910.14477 (replaced) [pdf, other]
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Title: Strictly linear light cones in long-range interacting systems of arbitrary dimensionsComments: 8 pages + 53 pages, 12 figures. [v.2] Typos are corrected and readability is improved. The result is slightly improved for few-body Hamiltonians. A discussion on the optimality is added. [v.3] Readability is further improvedSubjects: Quantum Physics (quant-ph); Disordered Systems and Neural Networks (cond-mat.dis-nn); Statistical Mechanics (cond-mat.stat-mech); High Energy Physics - Theory (hep-th); Mathematical Physics (math-ph)
In locally interacting quantum many-body systems, a velocity of the information propagation is finitely bounded and the linear light cone can be defined. Outside the light cone, amount of the information propagation rapidly decays with the distance. When systems have long-range interactions, it is highly nontrivial whether such a linear light cone exists or not. We herein consider generic long-range interacting systems with decaying interactions as $R^{-\alpha}$ with the distance $R$. We rigorously prove the existence of the linear light cone for $\alpha>2D+1$ ($D$: the spatial dimension), where we obtain the Lieb-Robinson bound as $\|[O_i(t),O_j]\|\lesssim{t}^{2D+1}(R-\bar{v}t)^{-\alpha}$ with $\bar{v}=\mathcal{O}(1)$ for arbitrary two operators $O_i$ and $O_j$ separated by a distance $R$. Moreover, we give an explicit quantum-state transfer protocol that achieves the above bound up to a constant coefficient and violates the linear light cone for $\alpha<2D+1$. This implies that our Lieb-Robinson bound is the best general upper bound in the regime of $\alpha>2D+1$.
- arXiv:1911.02228 (replaced) [pdf]
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Title: Enhancement of superconductivity in organic-inorganic hybrid topological materialsAuthors: Haoxiong Zhang, Awabaikeli Rousuli, Shengchun Shen, Kenan Zhang, Chong Wang, Laipeng Luo, Jizhang Wang, Yang Wu, Yong Xu, Wenhui Duan, Hong Yao, Pu Yu, Shuyun ZhouJournal-ref: Science Bulletin 65, 188-193 (2020)Subjects: Materials Science (cond-mat.mtrl-sci); Superconductivity (cond-mat.supr-con)
Inducing or enhancing superconductivity in topological materials is an important route toward topological superconductivity. Reducing the thickness of transition metal dichalcogenides (e.g. WTe2 and MoTe2) has provided an important pathway to engineer superconductivity in topological matters; for instance, emergent superconductivity with Tc=0.82 K was observed in monolayer WTe2 which also hosts intriguing quantum spin Hall effect, although the bulk crystal is nonsuperconducting. However, such monolayer sample is difficult to obtain, unstable in air, and with extremely low Tc, which could pose a grand challenge for practical applications. Here we report an experimentally convenient approach to control the interlayer coupling to achieve tailored topological properties, enhanced superconductivity and good sample stability through organic cation intercalation of the Weyl semimetals MoTe2 and WTe2. The as-formed organic-inorganic hybrid crystals are weak topological insulators with enhanced Tc of 7.0 K for intercalated MoTe2 (0.25 K for pristine crystal) and 2.3 K for intercalated WTe2 (2.8 times compared to monolayer WTe2). Such organic-cationintercalation method can be readily applied to many other layered crystals, providing a new pathway for manipulating their electronic, topological and superconducting properties.
- arXiv:1911.03957 (replaced) [pdf, other]
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Title: Gap states and valley-spin filtering in transition metal dichalcogenide monolayersComments: 5 pages, 2 figuresJournal-ref: Phys. Rev. B 101, 115423 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Quantum Physics (quant-ph)
The magnetically-induced valley-spin filtering in transition metal dichalcogenide monolayers ($MX_{2}$, where $M$=Mo, W and $X$=S, Se, Te) promises new paradigm in information processing. However, the detailed understanding of this effect is still limited, regarding its underlying transport processes. Herein, it is suggested that the filtering mechanism can be greately elucidated by the concept of metal-induced gap states (MIGS), appearing in the electrode-terminated $MX_{2}$ materials {\it i.e.} the referential filter setup. In particular, the gap states are predicted here to mediate valley- and spin-resolved charge transport near the ideal electrode/$MX_{2}$ interface, and therefore to initiate filtering. It is also argued that the role of MIGS increases when the channel length is diminished, as they begin to govern the overall valley-spin transport in the tunneling regime. In what follows, the presented study yields fundamental scaling trends for the valley-spin selectivity with respect to the intrinsic physics of the filter materials. As a result, it facilitates insight into the analyzed effects and provide design guidelines toward efficient valley-spin filter devices, that base on the discussed materials or other hexagonal monolayers with a broken inversion symmetry.
- arXiv:1911.05382 (replaced) [pdf, other]
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Title: Self-organized bistability and its possible relevance for brain dynamicsComments: 6 figuresJournal-ref: Phys. Rev. Research 2, 013318 (2020)Subjects: Statistical Mechanics (cond-mat.stat-mech); Adaptation and Self-Organizing Systems (nlin.AO); Neurons and Cognition (q-bio.NC)
Self-organized bistability (SOB) is the counterpart of 'self-organized criticality' (SOC), for systems tuning themselves to the edge of bistability of a discontinuous phase transition, rather than to the critical point of a continuous one. The equations defining the mathematical theory of SOB turn out to bear strong resemblance to a (Landau-Ginzburg) theory recently proposed to analyze the dynamics of the cerebral cortex. This theory describes the neuronal activity of coupled mesoscopic patches of cortex, homeostatically regulated by short-term synaptic plasticity. The theory for cortex dynamics entails, however, some significant differences with respect to SOB, including the lack of a (bulk) conservation law, the absence of a perfect separation of timescales and, the fact that in the former, but not in the second, there is a parameter that controls the overall system state (in blatant contrast with the very idea of self-organization). Here, we scrutinize --by employing a combination of analytical and computational tools-- the analogies and differences between both theories and explore whether in some limit SOB can play an important role to explain the emergence of scale-invariant neuronal avalanches observed empirically in the cortex. We conclude that, actually, in the limit of infinitely slow synaptic-dynamics, the two theories become identical, but the timescales required for the self-organization mechanism to be effective do not seem to be biologically plausible. We discuss the key differences between self-organization mechanisms with/without conservation and with/without infinitely separated timescales. In particular, we introduce the concept of 'self-organized collective oscillations' and scrutinize the implications of our findings in neuroscience, shedding new light into the problems of scale invariance and oscillations in cortical dynamics.
- arXiv:1911.11335 (replaced) [pdf, other]
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Title: Unification of Aeolian and Fluvial Sediment Transport Rate from Granular PhysicsJournal-ref: Phys. Rev. Lett. 124, 168001 (2020)Subjects: Soft Condensed Matter (cond-mat.soft); Atmospheric and Oceanic Physics (physics.ao-ph); Fluid Dynamics (physics.flu-dyn); Geophysics (physics.geo-ph)
One of the physically least understood characteristics of geophysical transport of sediments along sediment surfaces is the well known experimental observation that the sediment transport rate $Q$ is linearly dependent on the fluid shear stress $\tau$ applied onto the surface in air, but is nonlinearly dependent on $\tau$ in water. Using transport simulations for a wide range of driving conditions, we show that the scaling depends on the manner in which the kinetic fluctuation energy of transported particles is dissipated: via predominantly fluid drag and quasistatic contacts (linear) versus fluid drag and quasistatic and collisional contacts (nonlinear). We use this finding to derive a scaling law (asymptotically $Q\sim\tau^2$) in simultaneous agreement with measurements in water and air streams.
- arXiv:1912.07638 (replaced) [pdf, other]
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Title: Design and characterization of a quantum heat pump in a driven quantum gasComments: 6 pages, 5 figuresJournal-ref: Phys. Rev. E 101, 042109 (2020)Subjects: Quantum Gases (cond-mat.quant-gas); Statistical Mechanics (cond-mat.stat-mech); Quantum Physics (quant-ph)
We propose the implementation of a quantum heat pump with ultracold atoms. It is based on two periodically driven coherently coupled quantum dots using ultracold atoms. Each dot possesses two relevant quantum states and is coupled to a fermionic reservoir. The working principle is based on energy-selective driving-induced resonant tunneling processes, where a particle that tunnels from one dot to the other either absorbs or emits the energy quantum $\hbar\omega$ associated with the driving frequency, depending on its energy. We characterize the device using Floquet theory and compare simple analytical estimates to numerical simulations based on the Floquet-Born-Markov formalism. In particular, we show that driving-induced heating is directly linked to the micromotion of the Floquet states of the system.
- arXiv:1912.09643 (replaced) [pdf, ps, other]
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Title: Defect charging and resonant levels in half-Heusler Nb$_{1-x}$Ti$_x$FeSbAuthors: Yefan Tian, Farit G. Vagizov, Nader Ghassemi, Wuyang Ren, Hangtian Zhu, Zhiming Wang, Zhifeng Ren, Joseph H. Ross JrComments: 10 pages, 5 figuresSubjects: Materials Science (cond-mat.mtrl-sci)
We report $^{93}$Nb and $^{121}$Sb NMR and $^{57}$Fe M\"{o}ssbauer studies combined with DFT calculations of Nb$_{1-x}$Ti$_x$FeSb ($0\leqslant x \leqslant0.3$), one of the most promising thermoelectric systems for applications above 1000 K. These studies provide local information about defects and electronic configurations in these heavily $p$-type materials. The NMR spin-lattice relaxation rate provides a measure of states within the valence band. With increasing $x$, changes of relaxation rate vs carrier concentration for different substitution fractions indicate the importance of resonant levels which do not contribute to charge transport. The local paramagnetic susceptibility is significantly larger than expected based on DFT calculations, which we discuss in terms of an enhancement of the susceptibility due to a Coulomb enhancement mechanism. The M\"{o}ssbauer spectra of Ti-substituted samples show small departures from a binomial distribution of substituted atoms, while for unsubstituted $p$-type NbFeSb, the amplitude of a M\"{o}ssbauer satellite peak increases vs temperature, a measure of the $T$-dependent charging of a population of defects residing about 30 meV above the valence band edge, indicative of an impurity band at this location.
- arXiv:1912.11690 (replaced) [pdf, other]
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Title: Critical scaling of diffusion coefficients and size of rigid clusters of soft athermal particles under shearComments: 9 pages, 7 figuresSubjects: Soft Condensed Matter (cond-mat.soft)
We numerically investigate the self-diffusion coefficient and correlation length of the rigid clusters (i.e., the typical size of the collective motions) in sheared soft athermal particles. Here we find that the rheological flow curves on the self-diffusion coefficient are collapsed by the proximity to the jamming transition density. This feature is in common with the well-established critical scaling of flow curves on shear stress or viscosity. We furthermore reveal that the divergence of the correlation length governs the critical behavior of the diffusion coefficient, where the diffusion coefficient is proportional to the correlation length and the strain rate for a wide range of the strain rate and packing fraction across the jamming transition density.
- arXiv:1912.12668 (replaced) [pdf]
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Title: Room-Temperature Terahertz Anomalous Hall Effect in Weyl Antiferromagnet Mn$_3$Sn Thin FilmsAuthors: Takuya Matsuda, Natsuki Kanda, Tomoya Higo, N. P. Armitage, Satoru Nakatsuji, Ryusuke MatsunagaJournal-ref: Nature Communications 11, 909 (2020)Subjects: Materials Science (cond-mat.mtrl-sci)
Antiferromagnetic spin motion at terahertz (THz) frequencies attracts growing interests for fast spintronics, however their smaller responses to external field inhibit device application. Recently the noncollinear antiferromagnet Mn$_3$Sn, a Weyl semimetal candidate, was reported to show large anomalous Hall effect (AHE) at room temperature comparable to ferromagnets. Dynamical aspect of such large responses is an important issue to be clarified for future THz data processing. Here the THz anomalous Hall conductivity in Mn$_3$Sn thin films is investigated by polarization-resolved spectroscopy. Large anomalous Hall conductivity Re $\sigma_{xy} (\omega) \sim$ 20 $\rm{\Omega^{-1} cm^{-1}}$ at THz frequencies is clearly observed as polarization rotation. In contrast, Im $\sigma_{xy} (\omega)$ is small up to a few THz, showing that the AHE remains dissipationless over a large frequency range. A peculiar temperature dependence corresponding to the breaking/recovery of symmetry in the spin texture is also discussed. Observation of the THz AHE at room temperature demonstrates the ultrafast readout for the antiferromagnetic spintronics using Mn$_3$Sn and will also open new avenue for studying nonequilibrium dynamics in Weyl antiferromagnets.
- arXiv:2001.00586 (replaced) [pdf, other]
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Title: Hierarchy of energy scales in an O(3) symmetric antiferromagnetic quantum critical metal: a Monte Carlo studyComments: 13 pages, 18 figures, corrected affiliation information and acknowledgmentsJournal-ref: Phys. Rev. Research 2, 023008 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el); Superconductivity (cond-mat.supr-con)
We present numerically exact results from sign-problem free quantum Monte Carlo simulations for a spin-fermion model near an $O(3)$ symmetric antiferromagnetic (AFM) quantum critical point. We find a hierarchy of energy scales that emerges near the quantum critical point. At high energy scales, there is a broad regime characterized by Landau-damped order parameter dynamics with dynamical critical exponent $z=2$, while the fermionic excitations remain coherent. The quantum critical magnetic fluctuations are well described by Hertz-Millis theory, except for a $T^{-2}$ divergence of the static AFM susceptibility. This regime persists down to a lower energy scale, where the fermions become overdamped and concomitantly, a transition into a $d-$wave superconducting state occurs. These findings resemble earlier results for a spin-fermion model with easy-plane AFM fluctuations of an $O(2)$ SDW order parameter, despite noticeable differences in the perturbative structure of the two theories. In the $O(3)$ case, perturbative corrections to the spin-fermion vertex are expected to dominate at an additional energy scale, below which the $z=2$ behavior breaks down, leading to a novel $z=1$ fixed point with emergent local nesting at the hot spots [Schlief et al., PRX 7, 021010 (2017)]. Motivated by this prediction, we also consider a variant of the model where the hot spots are nearly locally nested. Within the available temperature range in our study ($T\ge E_F/200$), we find substantial deviations from the $z=2$ Hertz-Millis behavior, but no evidence for the predicted $z=1$ criticality.
- arXiv:2001.01009 (replaced) [pdf, other]
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Title: Observation of the Interlayer Exciton Gases in WSe$_2$ -pWSe$_2$ HeterostructuresAuthors: Zheng Sun, Jonathan Beaumariage, Qingrui Cao, Kenji Watanabe, Takashi Taniguchi, Benjamin Hunt, David W SnokeSubjects: Materials Science (cond-mat.mtrl-sci); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Interlayer excitons (IXs) possess a much longer lifetime than intralayer excitons due to the spatial separation of the electrons and holes; hence, they have been pursued to create exciton condensates for decades. The recent emergence of two-dimensional (2D) materials, such as transition metal dichalcogenides (TMDs), and of their van der Waals heterostructures (HSs), in which two different 2D materials are layered together, has created new opportunities to study IXs. Here we present the observation of IX gases within two stacked structures consisting of hBN/WSe$_2$/hBN/p: WSe$_2$/hBN. The IX energy of the two different structures differed by 82 meV due to the different thickness of the hBN spacer layer between the TMD layers. We demonstrate that the lifetime of the IXs is shortened when the temperature decreases or when the pump power increases. We attribute this nonlinear behavior to an Auger process.
- arXiv:2001.01142 (replaced) [pdf, other]
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Title: Analytical results for the capacitance of a circular plate capacitorComments: 9 pagesJournal-ref: Phys. Rev. Research 2, 013289 (2020)Subjects: Mathematical Physics (math-ph); Quantum Gases (cond-mat.quant-gas); Classical Analysis and ODEs (math.CA); Classical Physics (physics.class-ph)
We study the classic problem of the capacitance of a circular parallel plate capacitor. At small separations between the plates, it is initially considered in 19th century by Kirchhoff who found the leading and the subleading term in the capacitance. Despite a large interest in the problem, one and a half century later, analytically was found only the second subleading term. Using the recent advances in the asymptotic analysis of Fredholm integral equations of the second kind with finite support, here we study the one governing the circular capacitor, known as the Love equation. We found analytically many new subleading terms in the capacitance at small separations. We also calculated the asymptotic expansion at large separations, thus providing the two simple expressions which practically describe the capacitance at all distances. The approach described here could be used to find exact analytical expansions for the capacitance to an arbitrary number of terms in both regimes of small and large separations.
- arXiv:2001.04236 (replaced) [pdf, ps, other]
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Title: The quantum dynamical map of the spin boson modelAuthors: Inés de VegaComments: Suggestions, feedback and comments are welcome. Some references added and typos correctedSubjects: Quantum Physics (quant-ph); Soft Condensed Matter (cond-mat.soft)
One of the main frameworks to analyze the effects of the environment in a quantum computer is that of pure dephasing, where the dynamics of qubits can be characterised in terms of a well-known dynamical map. In this work we present a non-peturbative extension of such map beyond this simple pure-dephasing case, i.e. that is valid for a general spin coupled to a bosonic environment in a thermal state. To this aim, we use a Trotter decomposition and a Magnus expansion to simplify the unitary evolution operator in interaction picture. The proposed derivation can be extended to other finite-level open quantum systems including many body, initial system-environment correlated states, multiple-time correlation functions or quantum information protocols.
- arXiv:2002.03730 (replaced) [pdf, other]
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Title: Properties of phonon modes of ion trap quantum computer in the Aubry phaseComments: 10 pages, 5 figures in the main text, 8 figures in the appendix. Accepted for publication in Physical Review AJournal-ref: Phys. Rev. A 101, 032349 (2020)Subjects: Quantum Gases (cond-mat.quant-gas); Quantum Physics (quant-ph)
We study analytically and numerically the properties of phonon modes in an ion quantum computer. The ion chain is placed in a harmonic trap with an additional periodic potential which dimensionless amplitude $K$ determines three main phases available for quantum computations: at zero $K$ we have the case of Cirac-Zoller quantum computer, below a certain critical amplitude $K<K_c$ the ions are in the Kolmogorov-Arnold-Moser (KAM) phase, with delocalized phonon modes and free chain sliding, and above the critical amplitude $K>K_c$ ions are in the pinned Aubry phase with a finite frequency gap protecting quantum gates from temperature and other external fluctuations. For the Aubry phase, in contrast to the Cirac-Zoller and KAM phases, the phonon gap remains independent of the number of ions placed in the trap keeping a fixed ion density around the trap center. We show that in the Aubry phase the phonon modes are much better localized comparing to the Cirac-Zoller and KAM cases. Thus in the Aubry phase the recoil pulses lead to local oscillations of ions while in other two phases they spread rapidly over the whole ion chains making them rather sensible to external fluctuations. We argue that the properties of localized phonon modes and phonon gap in the Aubry phase provide advantages for the ion quantum computations in this phase with a large number of ions.
- arXiv:2002.05759 (replaced) [pdf, ps, other]
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Title: Quantum Chaos of Unitary Fermi Gases in Strong Pairing Fluctuation RegionComments: 7 pages, 4 FiguresSubjects: Quantum Gases (cond-mat.quant-gas)
The growth rate of the out-of-time-ordered correlator in a N-flavor Fermi gas is investigated and the Lyapunove exponent $\lambda_L$ is calculated to the order of $1/N$. We find that the Lyapunove exponent monotonically increases as the the interaction strength increases from the BCS limit to the unitary region. At the unitarity the Lyapunove exponent increases while the temperature drops and it can reach to the order of $\lambda_L\sim T$ around the critical temperature for the $N=1$ case. The system scrambles faster for stronger pairing fluctuations. At the BCS limit, the Lyapunov exponent behaviors as $\lambda_L\propto e^{\mu/T} a^2_s T^2/N$.
- arXiv:2002.07760 (replaced) [pdf, ps, other]
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Title: Determinantal Point Processes, Stochastic Log-Gases, and BeyondAuthors: Makoto KatoriComments: v2: LaTeX 79 pages, no figure. This manuscript was prepared for the mini course given at `Workshop on Probability and Stochastic Processes' held at Orange County, Coorg, India, from 23rd to 26th February, 2020, which was organized by the Indian Academy of Sciences, Bangalore. arXiv admin note: substantial text overlap with arXiv:1903.04945Subjects: Probability (math.PR); Statistical Mechanics (cond-mat.stat-mech); Mathematical Physics (math-ph); Exactly Solvable and Integrable Systems (nlin.SI)
A determinantal point process (DPP) is an ensemble of random nonnegative-integer-valued Radon measures, whose correlation functions are all given by determinants specified by an integral kernel called the correlation kernel. First we show our new scheme of DPPs in which a notion of partial isometies between a pair of Hilbert spaces plays an important role. Many examples of DPPs in one-, two-, and higher-dimensional spaces are demonstrated, where several types of weak convergence from finite DPPs to infinite DPPs are given. Dynamical extensions of DPP are realized in one-dimensional systems of diffusive particles conditioned never to collide with each other. They are regarded as one-dimensional stochastic log-gases, or the two-dimensional Coulomb gases confined in one-dimensional spaces. In the second section, we consider such interacting particle systems in one dimension. We introduce a notion of determinantal martingale and prove that, if the system has determinantal martingale representation (DMR), then it is a determinantal stochastic process (DSP) in the sense that all spatio-temporal correlation function are expressed by a determinant. In the last section, we construct processes of Gaussian free fields (GFFs) on simply connected proper subdomains of $\mathbb{C}$ coupled with interacting particle systems defined on boundaries of the domains. There we use multiple Schramm--Loewner evolutions (SLEs) driven by the interacting particle systems. We prove that, if the driving processes are time-changes of the log-gases studied in the second section, then the obtained GFF with multiple SLEs are stationary. The stationarity defines an equivalence relation of GFFs, which will be regarded as a generalization of the imaginary surface studied by Miller and Sheffield.
- arXiv:2003.00095 (replaced) [pdf, ps, other]
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Title: Entanglement and boundary entropy in quantum spin chains with arbitrary direction of the boundary magnetic fieldsComments: 14 pages 3 figures v2: some references were addedSubjects: Strongly Correlated Electrons (cond-mat.str-el); Statistical Mechanics (cond-mat.stat-mech)
We calculate the entanglement and the universal boundary entropy (BE) in the critical quantum spin chains, such as the transverse field Ising chain and the XXZ chain, with arbitrary direction of the boundary magnetic field (ADBMF). We determine the boundary universality class that an ADBMF induces. In particular, we show that the induced boundary conformal field theory (BCFT) depends on the point on the Bloch sphere where the boundary magnetic field directs. We show that the classification of the directions boils down to this simple fact that the boundary field breaks the bulk symmetry or not. We present a procedure to estimate the universal BE, based on the finite-size corrections of the entanglement entropy, that apply to ADBMF. To calculate the universal BE in the XXZ chain, we use density matrix renormalization group (DMRG). The transverse field XY chain with ADBMF after Jordan-Wigner (JW) transformation is not a quadratic free fermion Hamiltonian. We are able to map this model to a quadratic free fermion chain by introducing two extra ancillary spins coupled to the main chain at the boundaries, which makes the problem {\it{integrable}}. The eigenstates of the transverse field XY chain can be obtained by a proper projection in the enlarged chain. Using this mapping, we are able to calculate the entanglement entropy of the transverse field XY chain using the usual correlation matrix technique up to relatively large sizes.
- arXiv:2003.00139 (replaced) [pdf, other]
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Title: Functional Thermodynamics of Maxwellian Ratchets: Constructing and Deconstructing Patterns, Randomizing and Derandomizing BehaviorsComments: 16 pages, 7 figures; supplemental materials, 8 pages, 3 figures; this http URLSubjects: Statistical Mechanics (cond-mat.stat-mech); Information Theory (cs.IT); Dynamical Systems (math.DS); Chaotic Dynamics (nlin.CD)
Maxwellian ratchets are autonomous, finite-state thermodynamic engines that implement input-output informational transformations. Previous studies of these "demons" focused on how they exploit environmental resources to generate work: They randomize ordered inputs, leveraging increased Shannon entropy to transfer energy from a thermal reservoir to a work reservoir while respecting both Liouvillian state-space dynamics and the Second Law. However, to date, correctly determining such functional thermodynamic operating regimes was restricted to a very few engines for which correlations among their information-bearing degrees of freedom could be calculated exactly and in closed form---a highly restricted set. Additionally, a key second dimension of ratchet behavior was largely ignored---ratchets do not merely change the randomness of environmental inputs, their operation constructs and deconstructs patterns. To address both dimensions, we adapt recent results from dynamical-systems and ergodic theories that efficiently and accurately calculate the entropy rates and the rate of statistical complexity divergence of general hidden Markov processes. In concert with the Information Processing Second Law, these methods accurately determine thermodynamic operating regimes for finite-state Maxwellian demons with arbitrary numbers of states and transitions. In addition, they facilitate analyzing structure versus randomness trade-offs that a given engine makes. The result is a greatly enhanced perspective on the information processing capabilities of information engines. As an application, we give a thorough-going analysis of the Mandal-Jarzynski ratchet, demonstrating that it has an uncountably-infinite effective state space.
- arXiv:2003.01869 (replaced) [pdf, other]
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Title: Exactly solvable two-terminal heat engine with asymmetric Onsager coefficients: Origin of the power-efficiency boundComments: 7 pages, 3 figuresJournal-ref: Phys. Rev. E 101, 052132 (2020)Subjects: Statistical Mechanics (cond-mat.stat-mech)
An engine producing a finite power at the ideal (Carnot) efficiency is a dream engine, which is not prohibited by the thermodynamic second law. Some years ago, a two-terminal heat engine with {\em asymmetric} Onsager coefficients in the linear response regime was suggested by Benenti, Saito, and Casati [Phys. Rev. Lett. {\bf 106}, 230602 (2011)], as a prototypical system to make such a dream come true with non-divergent system parameter values. However, such a system has never been realized in spite of many trials. Here, we introduce an exactly solvable two-terminal Brownian heat engine with the asymmetric Onsager coefficients in the presence of a Lorenz (magnetic) force. Nevertheless, we show that the dream engine regime cannot be accessible even with the asymmetric Onsager coefficients, due to an instability keeping the engine from reaching its steady state. This is consistent with recent trade-off relations between the engine power and efficiency, where the (cyclic) steady-state condition is implicitly presumed. We conclude that the inaccessibility to the dream engine originates from the steady-state constraint on the engine.
- arXiv:2003.02711 (replaced) [pdf, ps, other]
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Title: Exact Overlap in the Lieb-Liniger Model from Coordinate Bethe AnsatzAuthors: Hui-Huang ChenComments: 12 pages, no figure. minor modifications, references addedSubjects: Statistical Mechanics (cond-mat.stat-mech); Mathematical Physics (math-ph)
In the paper arXiv:2002.12065, the authors developed a new method to compute the exact overlap formula between integrable boundary states and on-shell Bethe states in integrable spin chains. This method utilizes the coordinate Bethe ansatz representation of wave functions and singularity property of the off-shell overlaps. In this paper, we use this new method to derive the formula for overlap between the Lieb-Liniger Bethe states and the Bose-Einstein condensate (BEC) state. Our formula coincides with the earlier result.
- arXiv:2003.02852 (replaced) [pdf, other]
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Title: Superconducting islands with semiconductor-nanowire-based topological Josephson junctionsComments: 18 pages, 17 figures. See also accompanying paper arXiv:2003.02858Subjects: Superconductivity (cond-mat.supr-con); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We theoretically study superconducting islands based on semiconductor-nanowire Josephson junctions and take into account the presence of subgap quasiparticle excitations in the spectrum of the junction. Our method extends the standard model Hamiltonian for a superconducting charge qubit and replaces the Josephson potential by the Bogoliubov-de Gennes Hamiltonian of the nanowire junction, projected onto the relevant low-energy subgap subspace. This allows to fully incorporate the coherent dynamics of subgap levels in the junction. The combined effect of spin-orbit coupling and Zeeman energy in the nanowires forming the junction triggers a topological transition, where the subgap levels evolve from finite-energy Andreev bound states into near-zero energy Majorana bound states. The interplay between the microscopic energy scales governing the nanowire junction (the Josephson energy, the Majorana coupling and the Majorana energy splitting), with the charging energy of the superconducting island, gives rise to a great variety of physical regimes. Based on this interplay of different energy scales, we fully characterize the microwave response of the junction, from the Cooper pair box to the transmon regimes, and show how the presence of Majoranas can be detected through distinct spectroscopic features.
- arXiv:2003.02858 (replaced) [pdf, other]
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Title: Majorana oscillations and parity crossings in semiconductor-nanowire-based transmon qubitsComments: 6 pages, 3 Figures. See also accompanying paper arXiv:2003.02852Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Superconductivity (cond-mat.supr-con)
We show that the microwave (MW) spectra in semiconductor-nanowire-based transmon qubits provide a strong signature of the presence of Majorana bound states in the junction. This occurs as an external magnetic field tunes the wire into the topological regime and the energy splitting of the emergent Majorana modes oscillates around zero energy owing to spatial overlap in finite-length wires. In particular, we discuss how the zero-energy fermion parity crossings arising from Majorana oscillations result in distinct spectroscopic features. In split-junction geometries, the plasma mode couples to the phase-dispersing subgap levels resulting from Majorana hybridization via a Jaynes-Cummings-like interaction. As a consequence of this interaction, higher order plasma excitations in the junction inherit Majorana properties, including the $4\pi$ effect. Our results, based on a fully microscopic description of the junction, suggest that MW spectroscopy of nanowire-based transmon qubits provides an interesting alternative to Majorana detection by transport spectroscopy.
- arXiv:2003.03306 (replaced) [pdf, other]
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Title: Rotating mixed $^3$He-$^4$He nanodropletsComments: 6 pages, 4 figures (plus Supplemental Material). Revised version with corrections+missing figureSubjects: Quantum Gases (cond-mat.quant-gas)
Mixed $^3$He-$^4$He droplets created by hydrodynamic instability of a cryogenic fluid-jet may acquire angular momentum during their passage through the nozzle of the experimental apparatus. These free-standing droplets cool down to very low temperatures undergoing isotopic segregation, developing a nearly pure $^3$He crust surrounding a very $^4$He-rich superfluid core. Here, the stability and appearance of rotating mixed helium droplets are investigated using Density Functional Theory for an isotopic composition that highlights, with some marked exceptions related to the existence of the superfluid inner core, the analogies with viscous rotating droplets.
- arXiv:2003.03448 (replaced) [pdf]
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Title: Strengthening the magnetic interactions in pseudobinary first-row transition metal thiocyanates, $\it{M}$(NCS)$_{2}$Authors: Euan N. Bassey, Joseph A. M. Paddison, Evan N. Keyzer, Jeongjae Lee, Pascal Manuel, Ivan da Silva, Siân E. Dutton, Clare P. Grey, Matthew J. CliffeComments: 17 pages, 10 figuresSubjects: Materials Science (cond-mat.mtrl-sci); Strongly Correlated Electrons (cond-mat.str-el)
Understanding the effect of chemical composition on the strength of magnetic interactions is key to the design of magnets with stronger exchange interactions. The magnetic divalent first-row transition metal (TM) thiocyanates are a class of chemically simple layered molecular frameworks. Here, we report two new members of the family, manganese (II) thiocyanate, Mn(NCS)$_{2}$, and iron (II) thiocyanate, Fe(NCS)$_{2}$. Using magnetic susceptibility measurements on these materials and on cobalt (II) thiocyanate and nickel (II) thiocyanate, Co(NCS)$_{2}$ and Ni(NCS)$_{2}$, respectively, we identify significantly stronger net antiferromagnetic interactions between the earlier TM ions-a decrease in the Weiss constant, \theta, from 29 K for Ni(NCS)$_{2}$ to -115 K for Mn(NCS)$_{2}$-a consequence of more diffuse 3d orbitals, increased orbital overlap and increasing numbers of unpaired $\it{t}$$_{2g}$ electrons. We elucidate the magnetic structures of these materials: Mn(NCS)$_{2}$, Fe(NCS)$_{2}$ and Co(NCS)$_{2}$ order into the same antiferromagnetic commensurate ground state, whilst Ni(NCS)$_{2}$ adopts a ground state structure consisting of ferromagnetically ordered layers stacked antiferromagnetically. We show that magnetic molecular frameworks with significantly stronger net exchange interactions can be constructed by using earlier TMs.
- arXiv:2003.03594 (replaced) [pdf, ps, other]
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Title: Field-selective classical spin liquid and magnetization plateaus on kagome latticeComments: 7 pages, 7 figuresJournal-ref: J. Phys. Soc. Jpn. 89, 053708 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el); Materials Science (cond-mat.mtrl-sci); Statistical Mechanics (cond-mat.stat-mech)
We obtain a classical spin liquid (CSL) phase by applying a magnetic field in $J_1$-$J_2$-$J_3$ Ising model on a kagome lattice. As we proved in the previous study [Phys. Rev. Lett. {\bf 119}, 077207 (2017)], this model realizes one species of CSL, the hexamer CSL, at zero magnetic field, which consists of macroscopically degenerate spin configurations with mixed total magnetization, $M$. The magnetic field selects its subset, which can be mapped to a trimer covering of the dual lattice, and forms a magnetization plateau of $M=1/9$. In addition to this CSL, we find two other magnetization plateaus at $M=5/9$ and $17/27$, which are ascribed to the "multimer" superstructures on a dual lattice.
- arXiv:2003.03800 (replaced) [pdf, ps, other]
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Title: One or two small points in thermodynamicsAuthors: Walter F. WreszinskiComments: 33 pages, important conceptual additions and corrections in section 5Subjects: Statistical Mechanics (cond-mat.stat-mech); Mathematical Physics (math-ph)
I present my recollections of what I used to find to be "one or two small points in thermodynamics", following Sommerfeld's famous quote, and review them on the light of present knowledge.
- arXiv:2003.04299 (replaced) [pdf, other]
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Title: Discovering Symmetry Invariants and Conserved Quantities by Interpreting Siamese Neural NetworksSubjects: Computational Physics (physics.comp-ph); Disordered Systems and Neural Networks (cond-mat.dis-nn); Machine Learning (cs.LG)
In this paper, we introduce interpretable Siamese Neural Networks (SNN) for similarity detection to the field of theoretical physics. More precisely, we apply SNNs to events in special relativity, the transformation of electromagnetic fields, and the motion of particles in a central potential. In these examples, the SNNs learn to identify datapoints belonging to the same events, field configurations, or trajectory of motion. It turns out that in the process of learning which datapoints belong to the same event or field configuration, these SNNs also learn the relevant symmetry invariants and conserved quantities. These SNNs are highly interpretable, which enables us to reveal the symmetry invariants and conserved quantities without prior knowledge.
- arXiv:1807.03334 (replaced) [pdf, other]
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Title: An introduction to the SYK modelAuthors: Vladimir RosenhausComments: 20 pagesJournal-ref: J. Phys. A: Math. Theor. 52 (2019) 323001Subjects: High Energy Physics - Theory (hep-th); Strongly Correlated Electrons (cond-mat.str-el); General Relativity and Quantum Cosmology (gr-qc); Mathematical Physics (math-ph); Quantum Physics (quant-ph)
These notes are a short introduction to the Sachdev-Ye-Kitaev model. We discuss: SYK and tensor models as a new class of large N quantum field theories, the near-conformal invariance in the infrared, the computation of correlation functions, generalizations of SYK, and applications to AdS/CFT and strange metals.
- arXiv:1904.10692 (replaced) [pdf, other]
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Title: Active Learning Algorithm for Computational PhysicsComments: 7 pages, 8 figuresJournal-ref: Phys. Rev. Research 2, 013287 (2020)Subjects: Quantum Gases (cond-mat.quant-gas); Materials Science (cond-mat.mtrl-sci); Nuclear Theory (nucl-th); Computational Physics (physics.comp-ph)
In large-scale computation of physics problems, one often encounters the problem of determining a multi-dimensional function, which can be time-consuming when computing each point in this multi-dimensional space is already time-demanding. In the work, we propose that the active learning algorithm can speed up such calculations. The basic idea is to fit a multi-dimensional function by neural networks, and the key point is to make the query of labeled data economically by using a stratagem called "query by committee". We present the general protocol of this fitting scheme, as well as the procedure of how to further compute physical observables with the fitted functions. We show that this method can work well with two examples, which are quantum three-body problem in atomic physics and the anomalous Hall conductivity in condensed matter physics, respectively. In these examples, we show that one reaches an accuracy of few percent error for computing physical observables with less than $10\%$ of total data points compared with uniform sampling. With these two examples, we also visualize that by using the active learning algorithm, the required data are added mostly in the regime where the function varies most rapidly, which explains the mechanism for the efficiency of the algorithm. We expect broad applications of our method on various kind of computational physics problems.
- arXiv:1904.11324 (replaced) [pdf, other]
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Title: Scaling in the massive antiferromagnetic XXZ spin-1/2 chain near the isotropic pointAuthors: S. B. RutkevichComments: v3: 14 pages, 5 figures, extended version, two appendices addedJournal-ref: Phys. Rev. E 101, 032115 (2020)Subjects: Statistical Mechanics (cond-mat.stat-mech); Strongly Correlated Electrons (cond-mat.str-el)
The scaling limit of the Heisenberg XXZ spin chain at zero magnetic field is studied in the gapped antiferromagnetic phase. For a spin-chain ring having $N_x$ sites, the universal Casimir scaling function, which characterises the leading finite-size correction term in the large-$N_x$ expansion of the ground state energy, is calculated by numerical solution of the nonlinear integral equation of the convolution type. It is shown, that the same scaling function describes the temperature dependence of the free energy of the infinite XXZ chain at low enough temperatures in the gapped scaling regime.
- arXiv:1904.11691 (replaced) [pdf]
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Title: Phase-change silicon as an ultrafast active photonic platformAuthors: Letian Wang, Matthew Eliceiri, Yang Deng, Yoonsoo Rho, Wan Shou, Heng Pan, Jie Yao, Costas P. GrigoropoulosSubjects: Optics (physics.optics); Materials Science (cond-mat.mtrl-sci)
Phase change material (PCM) features distinct optical or electronic properties between amorphous and crystalline states. Recently, it starts to play a key role in the emerging photonic applications like optoelectronic display, dynamic wavefront control, on-chip photonic memory and computation. However, current PCMs do not refract effectively at visible wavelengths and suffer from deformation and decomposition, limiting the repeatability and vast visible wavelength applications. Silicon as the fundamental material for electronics and photonics, has never been considered as phase change material, due to its ultrafast crystallization kinetics. Here we show the striking fact that nanoscale silicon domains can be reversibly crystallized and amorphized under nanosecond laser pulses. For a typical disk resonator, it also provides a 25% non-volatile modulation at nanosecond time scale. We further show proof-of-concept experiments that such attributes could enable ultra-high resolution dielectric color display and dynamic visible wavefront control.
- arXiv:1906.07627 (replaced) [pdf, other]
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Title: Directional shift current in mirror-symmetric BC$_2$NComments: 6 pages, 3 figuresJournal-ref: Phys. Rev. Research 2, 013263 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We present a first-principles theoretical study of the shift current in a noncentrosymmetric polytype of graphitic BC$_2$N, and find that the photoconductivity exhibits two distinctive features at the band edge. First, it ranks among the largest bulk nonlinear responses reported to date, with the peak value occurring in an energy range suitable for optical manipulation. Secondly, it is strongly anisotropic, due to the vanishing of particular tensor components not foretold by phenomenological symmetry arguments; this is a consequence of dipole selection rules imposed by mirror symmetry, which imply that the relative parities between valence and conduction bands are key for determining the directionality of the band-edge response. Our work identifies graphitic BC$_2$N as a promising candidate for next-generation photovoltaics, and opens up a broad framework for future studies.
- arXiv:1906.11439 (replaced) [pdf, ps, other]
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Title: Signatures of quantum mechanical Zeeman effect in classical transport due to topological properties of two-dimensional spin-3/2 holesSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
The Zeeman interaction is a quantum mechanical effect that underpins spin-based quantum devices such as spin qubits. Typically, identification of the Zeeman interaction needs a large out-of-plane magnetic field coupled with ultralow temperatures, which limits the practicality of spin-based devices. However, in two-dimensional (2D) semiconductor holes, the strong spin-orbit interaction causes the Zeeman interaction to couple the spin, the magnetic field, and the momentum, and has terms with different winding numbers. In this work, we demonstrate a physical mechanism by which the Zeeman terms can be detected in classical transport. The effect we predict is very strong, and tunable by means of both the density and the in-plane magnetic field. It is a direct signature of the topological properties of the 2D hole system, and a manifestation in classical transport of an effect stemming from relativistic quantum mechanics. We discuss experimental observation and implications for quantum technologies.
- arXiv:1907.06169 (replaced) [pdf, ps, other]
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Title: Nonequilibrium-relaxation approach to quantum phase transitions: Nontrivial critical relaxation in cluster-update quantum Monte CarloComments: 5 pages, 4 figuresJournal-ref: Phys. Rev. E 101, 032105 (2020)Subjects: Statistical Mechanics (cond-mat.stat-mech)
Although the nonequilibrium relaxation (NER) method has been widely used in Monte Carlo studies on phase transitions in classical spin systems, such studies have been quite limited in quantum phase transitions. The reason is that relaxation process based on cluster-update quantum Monte Carlo (QMC) algorithms, which are now standards in Monte Carlo studies on quantum systems, has been considered "too fast" for such analyses. Recently the present authors revealed that the NER process in classical spin systems based on cluster-update algorithms is characterized by the stretched-exponential critical relaxation, rather than the conventional power-law one in local-update algorithms. In the present article we show that this is also the case in quantum phase transitions analyzed with the cluster-update QMC, and that advantages of NER analyses are available. As the simplest example of isotropic quantum spin models which exhibit quantum phase transitions, we investigate the N\'eel-dimer quantum phase transition in the two-dimensional $S=1/2$ columnar-dimerized antiferromagnetic Heisenberg model with the continuous-time loop algorithm.
- arXiv:1907.09956 (replaced) [pdf, other]
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Title: Optimal Wave Fields for Micro-manipulation in Complex Scattering EnvironmentsAuthors: Michael Horodynski, Matthias Kühmayer, Andre Brandstötter, Kevin Pichler, Yan V. Fyodorov, Ulrich Kuhl, Stefan RotterJournal-ref: Nature Photonics 14, 149 (2020)Subjects: Optics (physics.optics); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Soft Condensed Matter (cond-mat.soft)
The manipulation of small objects with light has become an indispensable tool in many areas of research ranging from physics to biology and medicine. Here we demonstrate how to implement micro-manipulation at the optimal level of efficiency for targets of arbitrary shape and inside complex environments such as disordered media. Our approach is to design wave-fronts in the far-field that have optimal properties in the near-field of the target such as to apply to it the strongest possible force, pressure or torque as well as to achieve the most efficient focus at the target position. Free of any iterative optimization, our approach only relies on a simple eigenvalue problem established from the scattering matrix of the system and its dependence on the target parameters. To illustrate this theoretical concept, we perform a proof-of-principle experiment in the microwave regime, which fully confirms our predictions.
- arXiv:1907.12069 (replaced) [pdf, other]
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Title: Archetypal soft-mode driven antipolar transition in francisite Cu3Bi(SeO3)2O2ClAuthors: Cosme Milesi-Brault, Constance Toulouse, Evan Constable, Hugo Aramberri, Virginie Simonet, Sophie de Brion, Helmuth Berger, Luigi Paolasini, Alexei Bosak, Jorge Íñiguez, Mael GuennouComments: 6 pages, 5 Figures, supplemental material includedJournal-ref: Phys. Rev. Lett. 124, 097603 (2020)Subjects: Materials Science (cond-mat.mtrl-sci)
Model materials are precious test cases for elementary theories and provide building blocks for the understanding of more complex cases. Here, we describe the lattice dynamics of the structural phase transition in francisite Cu3Bi(SeO3)2O2Cl at 115 K and show that it provides a rare archetype of a transition driven by a soft antipolar phonon mode. In the high-symmetry phase at hightemperatures, the soft mode is found at (0,0,0.5) at the Brillouin zone boundary and is measured by inelastic X-ray scattering and thermal diffuse scattering. In the low-symmetry phase, this softmode is folded back onto the center of the Brillouin zone as a result of the doubling of the unit cell, and appears as a fully symmetric mode that can be tracked by Raman spectroscopy. On both sides of the transition, the mode energy squared follows a linear behaviour over a large temperature range. First-principles calculations reveal that, surprisingly, the flat phonon band calculated for the high-symmetry phase seems incompatible with the displacive character found experimentally. We discuss this unusual behavior in the context of an ideal Kittel model of an antiferroelectric transition.
- arXiv:1908.05011 (replaced) [pdf, other]
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Title: Rivalry of diffusion, external field and gravity in micro-convection of magnetic colloidsComments: Published in JMMM, in ICMF2019 special issue. Uses Elsevier templateJournal-ref: Journal of Magnetism and Magnetic Materials 498 (2020) 166247Subjects: Soft Condensed Matter (cond-mat.soft); Fluid Dynamics (physics.flu-dyn)
Magnetic fields and magnetic materials have promising microfluidic applications. For example, magnetic micro-convection can enhance mixing considerably. However, previous studies have not explained increased effective diffusion during this phenomenon. Here we show that enhanced interface smearing comes from a gravity induced convective motion within a thin microfluidic channel, caused by a small density difference between miscible magnetic and non-magnetic fluids. This motion resembles diffusive behavior and can be described with an effective diffusion coefficient. We explain this with a theoretical model, based on a dimensionless gravitational Rayleigh number, and verify it by numerical simulations and experiments with different cell thicknesses. Results indicate the applicability and limitations for microfluidic applications of other colloidal systems. Residual magnetic micro-convection follows earlier predictions.
- arXiv:1909.00336 (replaced) [pdf, ps, other]
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Title: Order in the ground state of a simple cubic dipole lattice in an external fieldComments: 16 pages (preprint), 4 figuresJournal-ref: Int. J. Quantum Chem. 120, e26053 (2020)Subjects: Other Condensed Matter (cond-mat.other); Materials Science (cond-mat.mtrl-sci)
Motivated by the presence of a lattice of rotating molecular dipoles in the high temperature phase of methylammonium lead iodide, we investigate the ground state of a simple cubic lattice of dipoles interacting with each other via the dipole-dipole interaction and with an external field via the Zeeman interaction. In the absence of an external field, the ground state is infinitely degenerate, and all the configurations in the ground state manifold are periodic along the three lattice axes with period 2. We numerically determine the ground state of a 1000-dipole lattice interacting with an external field, and we analyze the polarization, dipole orientation statistics and correlations in this state. These calculations show that for some special directions of the external field the two-site periodicity in the dipole configurations is preserved, while in the general case this periodicity is lost and complex dipole configurations form in the presence of the external field.
- arXiv:1909.02113 (replaced) [pdf]
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Title: Single femtosecond laser pulse interaction with micaSubjects: Materials Science (cond-mat.mtrl-sci); Applied Physics (physics.app-ph); Optics (physics.optics)
Ultrafast, femtosecond laser pulse interaction with dielectric materials has shown them to have significantly higher laser fluence threshold requirements, as compared to metals and semiconductors, for laser material modification, such as laser ablation. Examples of dielectrics are crystalline materials such as quartz and sapphire, and amorphous glasses. The interaction between femtosecond laser pulses, at a wavelength with negligible linear absorption, and a dielectric has been found to be weak, and multiple pulse irradiation is therefore typically used in order to see significant and quantifiable effects. In this study the dielectric is the crystalline, layered, natural mineral muscovite, a mica with formula KAl_2 (Si_3 Al) O_10 (OH)_2. Muscovite, newly cleaved, is used in a wide range of technological and scientific applications including as an insulating material in electronics and as an ultra-flat and ultra-clean substrate. A single, ~800 nm wavelength, ~6 micron spotsize, ~150 fs laser pulse is found to lead to a systematic range of laser modification topologies, as a function of the fluence of the single laser pulse, including bulk removal of material. The fs laser pulse/material interaction is greater than expected for a standard dielectric at a given fluence. Optical surface profiling and FESEM are used to characterise the topologies. Contrasting the results of the two techniques supports the use of optical surface profiling to characterise the material modification despite its limitations in lateral resolution as compared to FESEM. The interlayer mineral water content of natural muscovite is proposed as the primary reason that mica behaves differently to a standard dielectric when irradiated with a single 800 nm fs laser pulse.
- arXiv:1909.03844 (replaced) [pdf, other]
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Title: Impact of electron solvation on ice structures at the molecular scaleAuthors: Cord Bertram, Philipp Auburger, Michel Bockstedte, Julia Stähler, Uwe Bovensiepen, Karina MorgensternJournal-ref: J. Phys. Chem. Lett. 2020, 11, 1310-1316Subjects: Materials Science (cond-mat.mtrl-sci)
We determine the impact of electron solvation on D$_2$O structures adsorbed on Cu(111) with low temperature scanning tunneling microscopy, two-photon photoemission, and ab initio theory. UV photons generating solvated electrons lead not only to transient, but also to permanent structural changes through the rearrangement of individual molecules. The persistent changes occur near sites with a high density of dangling OH groups that facilitate electron solvation. We conclude that energy dissipation during solvation triggers permanent molecular rearrangement via vibrational excitation.
- arXiv:1909.06552 (replaced) [pdf, other]
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Title: Phonon thermal Hall effect in strontium titanateComments: Main text: 6 pages, 4 figures, Supplemental Material is included. Accepted by Phys. Rev. LettJournal-ref: Phys. Rev. Lett. 124, 105901 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el); Materials Science (cond-mat.mtrl-sci); Superconductivity (cond-mat.supr-con)
It has been known for more than a decade that phonons can produce an off-diagonal thermal conductivity in presence of magnetic field. Recent studies of thermal Hall conductivity, $\kappa_{xy}$, in a variety of contexts, however, have assumed a negligibly small phonon contribution. We present a study of $\kappa_{xy}$ in quantum paraelectric SrTiO$_3$, which is a non-magnetic insulator and find that its peak value exceeds what has been reported in any other insulator, including those in which the signal has been qualified as 'giant'. Remarkably, $\kappa_{xy}(T)$ and $\kappa(T)$ peak at the same temperature and the former decreases faster than the latter at both sides of the peak. Interestingly, in the case of La$_2$CuO$_4$ and $\alpha$-RuCl$_3$, $\kappa_{xy}(T)$ and $\kappa(T)$ peak also at the same temperature. We also studied KTaO$_3$ and found a small signal, indicating that a sizable $\kappa_{xy}(T)$ is not a generic feature of quantum paraelectrics. Combined to other observations, this points to a crucial role played by antiferrodistortive domains in generating $\kappa_{xy}$ of this solid.
- arXiv:1910.02528 (replaced) [pdf, other]
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Title: Computational models for active matterComments: 23 pages, 9 display itemsJournal-ref: Nature Review Physics 2, 181 (2020)Subjects: Soft Condensed Matter (cond-mat.soft); Biological Physics (physics.bio-ph); Computational Physics (physics.comp-ph)
A variety of computational models have been developed to describe active matter at different length and time scales. The diversity of the methods and the challenges in modeling active matter---ranging from molecular motors and cytoskeletal filaments over artificial and biological swimmers on microscopic to groups of animals on macroscopic scales---mainly originate from their out-of-equilibrium character, multiscale nature, nonlinearity, and multibody interactions. In the present review, various modeling approaches and numerical techniques are addressed, compared, and differentiated to illuminate the innovations and current challenges in understanding active matter. The complexity increases from minimal microscopic models of dry active matter toward microscopic models of active matter in fluids. Complementary, coarse-grained descriptions and continuum models are elucidated. Microscopic details are often relevant and strongly affect collective behaviors, which implies that the selection of a proper level of modeling is a delicate choice, with simple models emphasizing universal properties and detailed models capturing specific features. Finally, current approaches to further advance the existing models and techniques to cope with real-world applications, such as complex media and biological environments, are discussed.
- arXiv:1911.04728 (replaced) [pdf, other]
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Title: Coherent pumping of high momentum magnons by lightJournal-ref: Phys. Rev. B 101, 100401 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We propose to excite a large number of coherent magnons with high momentum in optical cavities. This is achieved by two counterpropagating optical modes that are detuned by the frequency of a selected magnon, similar to stimulated Raman scattering. In sub-mm size yttrium iron garnet spheres, a mW laser input power generates 10^6-10^8 coherent magnons. The large magnon population enhances Brillouin light scattering, a probe suitable to access their quantum properties.
- arXiv:1912.08123 (replaced) [pdf, other]
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Title: Microscopic theory of the friction force exerted on a quantum impurity in one-dimensional quantum liquidsAuthors: Aleksandra PetkovicComments: 12 pages and one figure; to appear in Physical Review BJournal-ref: Phys. Rev. B 101, 104503 (2020)Subjects: Quantum Gases (cond-mat.quant-gas); Statistical Mechanics (cond-mat.stat-mech)
We study the motion of a slow quantum impurity in one-dimensional environments focusing on systems of strongly interacting bosons and weakly interacting fermions. While at zero temperature the impurity motion is frictionless, at low temperatures finite friction appears. The dominant process is the scattering of the impurity off two fermionic quasiparticles. We evaluate the friction force and show that, at low temperatures, it scales either as the fourth or the sixth power of temperature, depending on the system parameters. This is a result of the scattering of the impurity off two fermionic quasiparticles that are situated around different Fermi points. It is the dominant process at low temperatures. We also evaluate the contribution to the friction force originating from the scattering of the impurity off two fermionic quasiparticles that are situated around different Fermi points. It behaves as the tenth power of temperature.
- arXiv:2002.05085 (replaced) [pdf, other]
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Title: Bouncing, chasing or pausing: asymmetric collisions of active dropletsComments: 7 pages, 5 figures, to appear in Physical Review FluidsJournal-ref: Phys. Rev. Fluids, 2020, 5, 032201Subjects: Fluid Dynamics (physics.flu-dyn); Soft Condensed Matter (cond-mat.soft); Biological Physics (physics.bio-ph); Chemical Physics (physics.chem-ph)
Chemically-active droplets exhibit complex avoiding trajectories. While heterogeneity is inevitable in active matter experiments, it is mostly overlooked in their modelling. Exploiting its geometric simplicity, we fully-resolve the head-on collision of two swimming droplets of different radii and demonstrate that even a small contrast in size critically conditions their collision and subsequent dynamics. We identify three fundamentally-different regimes. The resulting high sensitivity of pairwise collisions is expected to profoundly affect their collective dynamics.
- arXiv:2002.08172 (replaced) [pdf]
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Title: Spatially-resolved luminescence and crystal structure of single core-shell nanowires measured in the as-grown geometryAuthors: Ali AlHassan, Jonas Lähnemann, Steven Leake, Hanno Küpers, Michael Niehle, Danial Bahrami, Florian Bertram, Ryan B. Lewis, Arman Davtyan, Tobias Schülli, Lutz Geelhaar, Ullrich PietschComments: This is an author-created, un-copyedited version of an article published in Nanotechnology. IOP Publishing Ltd. is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at this https URLJournal-ref: Nanotechnology 31, 214002 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci); Applied Physics (physics.app-ph)
We report on the direct correlation between the structural and optical properties of single, as-grown core-multi-shell GaAs/In$_{0.15}$Ga$_{0.85}$As/GaAs/AlAs/GaAs nanowires. Fabricated by molecular beam epitaxy on a pre-patterned Si(111) substrate, on a row of well separated nucleation sites, it was possible to access individual nanowires in the as-grown geometry. The polytype distribution along the growth axis of the nanowires was revealed by synchrotron-based nanoprobe X-ray diffraction techniques monitoring the axial 111 Bragg reflection. For the same nanowires, the spatially-resolved emission properties were obtained by cathodoluminescence hyperspectral linescans in a scanning electron microscope. Correlating both measurements, we reveal a blueshift of the shell quantum well emission energy combined with an increased emission intensity for segments exhibiting a mixed structure of alternating wurtzite and zincblende stacking compared with the pure crystal polytypes. The presence of this mixed structure was independently confirmed by cross-sectional transmission electron microscopy.
- arXiv:2002.09171 (replaced) [pdf, ps, other]
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Title: Computing 3D chromatin configurations from contact probability maps by Inverse Brownian DynamicsComments: 22 pages, 8 figures, supplementary material (see ancillary directory), to appear in Biophysical JournalJournal-ref: Biophysical Journal 118 (2020) 1-16Subjects: Soft Condensed Matter (cond-mat.soft)
The three-dimensional organization of chromatin, on the length scale of a few genes, is crucial in determining the functional state - accessibility and the amount of gene expression - of the chromatin. Recent advances in chromosome conformation capture experiments provide partial information on the chromatin organization in a cell population, namely the contact count between any segment pairs, but not on the interaction strength that leads to these contact counts. However, given the contact matrix, determining the complete 3D organization of the whole chromatin polymer is an inverse problem. In the present work, a novel Inverse Brownian Dynamics (IBD) method based on a coarse grained bead-spring chain model has been proposed to compute the optimal interaction strengths between different segments of chromatin such that the experimentally measured contact count probability constraints are satisfied. Applying this method to the {\alpha}-globin gene locus in two different cell types, we predict the 3D organizations corresponding to active and repressed states of chromatin at the locus. We show that the average distance between any two segments of the region has a broad distribution and cannot be computed as a simple inverse relation based on the contact probability alone. The results presented for multiple normalization methods suggest that all measurable quantities may crucially depend on the nature of normalization. We argue that by experimentally measuring predicted quantities, one may infer the appropriate form of normalization.
- arXiv:2002.10600 (replaced) [pdf, other]
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Title: Modeling intermolecular and intramolecular modes of liquid water using multiple heat baths: Machine learning approachJournal-ref: J. Chem. Theory. Comput. 16, 2099 (2020)Subjects: Soft Condensed Matter (cond-mat.soft); Statistical Mechanics (cond-mat.stat-mech); Chemical Physics (physics.chem-ph)
The vibrational motion of molecules in dissipative environments, such as solvation and protein molecules, is composed of contributions from both intermolecular and intramolecular modes. The existence of these collective modes introduces difficulty into quantum simulations of chemical and biological processes. In order to describe the complex molecular motion of the environment in a simple manner, we introduce a system-bath model in which the intramolecular modes with anharmonic mode-mode couplings are described by a system Hamiltonian, while the other degrees of freedom, arising from the environmental molecules, are described by heat bath. Employing a machine-learning based approach, we determine not only the system parameters of the intramolecular modes but also the spectral distribution of the system-bath coupling to describe the intermolecular modes, using the atomic trajectories obtained from molecular dynamics (MD) simulations. The capabilities of the present approach are demonstrated for liquid water using MD trajectories calculated from the SPC/E model and the polarizable water model for intramolecular and intermolecular vibrational spectroscopies (POLI2VS) by determining the system parameters describing the symmetric-stretch, asymmetric-stretch and bend modes with intramolecular interactions and the bath spectral distribution functions for each intramolecular mode representing the interaction with the intra-molecular modes. From these results, we were able to elucidate the energy relaxation pathway between the intramolecular modes and the intermolecular modes in a non-intuitive manner.
- arXiv:2003.01459 (replaced) [pdf, ps, other]
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Title: Heat flux sensing by anomalous Nernst effect in Fe-Al thin films on a flexible substrateComments: 11 pages, 4 figuresJournal-ref: Appl. Phys. Express 13, 043001 (2020)Subjects: Materials Science (cond-mat.mtrl-sci)
We performed a numerical analysis of the material parameters required for realizing a heat flux sensor exploiting the anomalous Nernst effect (ANE). The results showed the importance of high thermopower of ANE ($S_{\text{ANE}}$) and small saturation magnetization. This motivated us to investigate the effect of Al substitution of Fe on ANE and found $S_{\text{ANE}} =$ 3.4 $\mu$V/K in Fe$_{81}$Al$_{19}$ because of the dominant intrinsic mechanism. Using this material, we made a prototype ANE-based heat flux sensor on a thin flexible polyimide sheet and demonstrated accurate sensing with it. This study gives important information for enhancing sensor sensitivity.
Crosses
- arXiv:1912.07577 (cross-list from quant-ph) [pdf, other]
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Title: Quantum Computer Systems for Scientific DiscoveryAuthors: Yuri Alexeev, Dave Bacon, Kenneth R. Brown, Robert Calderbank, Lincoln D. Carr, Frederic T. Chong, Brian DeMarco, Dirk Englund, Edward Farhi, Bill Fefferman, Alexey V. Gorshkov, Andrew Houck, Jungsang Kim, Shelby Kimmel, Michael Lange, Seth Lloyd, Mikhail D. Lukin, Dmitri Maslov, Peter Maunz, Christopher Monroe, John Preskill, Martin Roetteler, Martin Savage, Jeff ThompsonSubjects: Quantum Physics (quant-ph); Other Condensed Matter (cond-mat.other); High Energy Physics - Lattice (hep-lat); High Energy Physics - Theory (hep-th); Nuclear Theory (nucl-th)
The great promise of quantum computers comes with the dual challenges of building them and finding their useful applications. We argue that these two challenges should be considered together, by co-designing full-stack quantum computer systems along with their applications in order to hasten their development and potential for scientific discovery. In this context, we identify scientific and community needs, opportunities, a sampling of a few use case studies, and significant challenges for the development of quantum computers for science over the next 2--10 years. This document is written by a community of university, national laboratory, and industrial researchers in the field of Quantum Information Science and Technology, and is based on a summary from a U.S. National Science Foundation workshop on Quantum Computing held on October 21--22, 2019 in Alexandria, VA.
- arXiv:2003.03926 (cross-list from quant-ph) [pdf, ps, other]
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Title: Spectral characterization of non-Gaussian quantum noise: Keldysh approach and application to photon shot noiseSubjects: Quantum Physics (quant-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Having accurate tools to describe non-classical, non-Gaussian environmental fluctuations is crucial for designing effective quantum control protocols. We show how the Keldysh approach to quantum noise characterization can be usefully employed to characterize frequency-dependent noise, focusing on the quantum bispectrum (i.e. frequency-resolved third cumulant). Using the paradigmatic example of photon shot noise fluctuations in a driven bosonic mode, we show that the quantum bispectrum can be a powerful tool for revealing distinctive non-classical noise properties, including an effective breaking of detailed balance by quantum fluctuations. The Keldysh-ordered quantum bispectrum can be directly accessed using existing noise spectroscopy protocols.
- arXiv:2003.04000 (cross-list from q-bio.NC) [pdf, ps, other]
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Title: Theta-nested gamma oscillations in next generation neural mass modelsComments: 28 pages, 14 figuresSubjects: Neurons and Cognition (q-bio.NC); Disordered Systems and Neural Networks (cond-mat.dis-nn); Adaptation and Self-Organizing Systems (nlin.AO); Chaotic Dynamics (nlin.CD); Biological Physics (physics.bio-ph)
Theta-nested gamma oscillations have been reported in many areas of the brain and are believed to represent a fundamental mechanism to transfer information across spatial and temporal scales. In a series of recent experiments in vitro it has been possible to replicate with an optogenetic theta frequency stimulation several features of cross-frequency coupling among theta and gamma rhythms observed in behaving animals. In order to reproduce the main findings of these experiments we have considered a new class of neural mass models able to reproduce exactly the macroscopic dynamics of spiking neural networks. In this framework, we have examined two set-ups able to support collective gamma oscillations: the pyramidal interneuronal network gamma (PING) and the interneuronal network gamma (ING). In both set-ups we observe the emergence of theta-nested gamma oscillations by driving the system with a sinusoidal theta-forcing in proximity of a Hopf bifurcation. These mixed rhythms display always phase amplitude coupling. However 2 different types of nested oscillations can be identified: one characterized by a perfect phase locking between theta and gamma rhythms, corresponding to an overall periodic behaviour; another one where the locking is imperfect and the dynamics is quasi-periodic or even chaotic. From our analysis it emerges that the locked states are more frequent in the ING set-up. In agreement with the experiments, we find theta-nested gamma oscillations for forcing frequencies in the range [1:10] Hz, whose amplitudes grow proportionally to the forcing one and which are clearly modulated by the theta phase. At variance with experimental findings, the gamma-power peak does not shift to higher frequencies by increasing the theta frequency. This effect can be obtained, in or model, only by incrementing, at the same time, also the noise or the forcing amplitude.
- arXiv:2003.04154 (cross-list from cond-mat.quant-gas) [pdf, other]
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Title: Effective triangular ladders with staggered flux from spin-orbit coupling in 1D optical latticesComments: 12 pages, 6 figures. Accepted for publication in The European Physical Journal D, Topical issue: Topological Ultracold Atoms and Photonic SystemsSubjects: Quantum Gases (cond-mat.quant-gas); Strongly Correlated Electrons (cond-mat.str-el); Quantum Physics (quant-ph)
Light-induced spin-orbit coupling is a flexible tool to study quantum magnetism with ultracold atoms. In this work we show that spin-orbit coupled Bose gases in a one-dimensional optical lattice can be mapped into a two-leg triangular ladder with staggered flux following a lowest-band truncation of the Hamiltonian. The effective flux and the ratio of the tunneling strengths can be independently adjusted to a wide range of values. We identify a certain regime of parameters where a hard-core boson approximation holds and the system realizes a frustrated triangular spin ladder with tunable flux. We study the properties of the effective spin Hamiltonian using the density-matrix renormalization-group method and determine the phase diagram at half-filling. It displays two phases: a uniform superfluid and a bond-ordered insulator. The latter can be stabilized only for low Raman detuning. Finally, we provide experimentally feasible trajectories across the parameter space of the SOC system that cross the predicted phase transition.
Thu, 12 Mar 2020
- arXiv:2003.04898 [pdf, other]
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Title: The pyrochlore S=1/2 Heisenberg antiferromagnet at finite temperatureComments: 23 pages, 15 figuresSubjects: Strongly Correlated Electrons (cond-mat.str-el)
Frustrated three dimensional quantum magnets are notoriously impervious to theoretical analysis. Here we use a combination of three computational methods to investigate the three dimensional pyrochlore $S=1/2$ quantum antiferromagnet, an archetypical frustrated magnet, at finite temperature, $T$: canonical typicality for a finite cluster of $2\times 2 \times 2$ unit cells (i.e. $32$ sites), a finite-$T$ matrix product state method on a larger cluster with $48$ sites, and the numerical linked cluster expansion (NLCE) using clusters up to $25$ lattice sites, which include non-trivial hexagonal and octagonal loops. We focus on thermodynamic properties (energy, specific heat capacity, entropy, susceptibility, magnetisation) next to the static structure factor. We find a pronounced maximum in the specific heat at $T = 0.57 J$, which is stable across finite size clusters and converged in the series expansion. This is well-separated from a residual amount of spectral weight of $0.47 k_B \ln 2$ per spin which has not been released even at $T\approx0.25 J$, the limit of convergence of our results. This is a large value compared to a number of highly frustrated models and materials, such as spin ice or the kagome $S=1/2$ Heisenberg antiferromagnet. We also find a non-monotonic dependence on $T$ of the magnetisation at low magnetic fields, reflecting the dominantly non-magnetic character of the low-energy spectral weight. A detailed comparison of our results to measurements for the $S=1$ material NaCaNi$_2$F$_7$ yields rough agreement of the functional form of the specific heat maximum, which in turn differs from the sharper maximum of the heat capacity of the spin ice material Dy$_2$Ti$_2$O$_7$, all of which are yet qualitatively distinct from conventional, unfrustrated magnets.
- arXiv:2003.04901 [pdf, other]
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Title: Disorder-free localization in an interacting two-dimensional lattice gauge theoryComments: 5 pages, 3 figures, Supplementary MaterialsSubjects: Strongly Correlated Electrons (cond-mat.str-el); Statistical Mechanics (cond-mat.stat-mech); Quantum Physics (quant-ph)
Disorder-free localization has been recently introduced as a mechanism for ergodicity breaking in low-dimensional homogeneous lattice gauge theories caused by local constraints imposed by gauge invariance. We show that also genuinely interacting systems in two spatial dimensions can become nonergodic as a consequence of this mechanism. Specifically, we prove nonergodic behavior in the quantum link model by obtaining a rigorous bound on the localization-delocalization transition through a classical correlated percolation problem implying a fragmentation of Hilbert space on the nonergodic side of the transition. We study the quantum dynamics in this system by means of an efficient and perturbatively controlled representation of the wavefunction in terms of a variational network of classical spins akin to artificial neural networks. We identify a distinguishing dynamical signature by studying the propagation of line defects, yielding different light cone structures in the localized and ergodic phases, respectively. The methods we introduce in this work can be applied to any lattice gauge theory with finite-dimensional local Hilbert spaces irrespective of spatial dimensionality.
- arXiv:2003.04909 [pdf, other]
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Title: Topological phase transitions in four dimensionsComments: 11 pages, 1 figureSubjects: Quantum Gases (cond-mat.quant-gas); High Energy Physics - Theory (hep-th)
We show that four-dimensional systems may exhibit a topological phase transition analogous to the well-known Berezinskii-Kosterlitz-Thouless vortex unbinding transition in two-dimensional systems. The realisation of an engineered quantum system, where the predicted phase transition shall occur, is also presented. We study a suitable generalization of the sine-Gordon model in four dimensions and the renormalization group flow equation of its couplings, showing that the critical value of the frequency is the square of the corresponding value in $2D$. The value of the anomalous dimension at the critical point is determined ($\eta=1/32$) and a conjecture for the universal jump of the superfluid stiffness ($4/\pi^2$) presented.
- arXiv:2003.04922 [pdf]
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Title: Machine-learning assisted cross-domain prediction of ionic conductivity in sodium and lithium-based superionic conductorsComments: 26 pagesSubjects: Materials Science (cond-mat.mtrl-sci)
Solid state lithium- and sodium-ion batteries utilize solid ionicly conducting compounds as electrolytes. However, the ionic conductivity of such materials tends to be lower than their liquid counterparts, necessitating research efforts into finding suitable alternatives. The process of electrolyte screening is often based on a mixture of domain expertise and trial-and-error, both of which are time and resource-intensive. Data-driven and machine learning approaches have recently come to the fore to accelerate learnings towards discovery. In this work, we present a simple machine-learning based approach to predict the ionic conductivity of sodium and lithium-based SICON compounds. Using primarily theoretical elemental feature descriptors derivable from tabulated information on the unit cell and the atomic properties of the components of a target compound on a limited dataset of 70 NASICON-examples, we have designed a logistic regression-based model capable of distinguishing between poor and good superionic conductors with a cross-validation accuracy of over 82%. Moreover, we demonstrate how such a system is capable of cross-domain classification on lithium-based examples at the same accuracy, despite being introduced to zero lithium-based compounds during training. Through a systematic permutation-based evaluation process, we reduced the number of considered features from 47 to 7, reduction of over 83%, while simultaneously improving model performance. The contributions of different electronic and structural features to overall ionic conductivity is also discussed, and contrasted with accepted theories in literature. Our results demonstrate the utility of such a simple, yet interpretable tool provides opportunities for initial screening of potential candidates as solid-state electrolytes through the use of existing data.
- arXiv:2003.04934 [pdf, other]
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Title: Automated discovery of a robust interatomic potential for aluminumAuthors: Justin S. Smith, Benjamin Nebgen, Nithin Mathew, Jie Chen, Nicholas Lubbers, Leonid Burakovsky, Sergei Tretiak, Hai Ah Nam, Timothy Germann, Saryu Fensin, Kipton BarrosSubjects: Materials Science (cond-mat.mtrl-sci); Machine Learning (cs.LG); Computational Physics (physics.comp-ph)
Atomistic molecular dynamics simulation is an important tool for predicting materials properties. Accuracy depends crucially on the model for the interatomic potential. The gold standard would be quantum mechanics (QM) based force calculations, but such a first-principles approach becomes prohibitively expensive at large system sizes. Efficient machine learning models (ML) have become increasingly popular as surrogates for QM. Neural networks with many thousands of parameters excel in capturing structure within a large dataset, but may struggle to extrapolate beyond the scope of the available data. Here we present a highly automated active learning approach to iteratively collect new QM data that best resolves weaknesses in the existing ML model. We exemplify our approach by developing a general potential for elemental aluminum. At each active learning iteration, the method (1) trains an ANI-style neural network potential from the available data, (2) uses this potential to drive molecular dynamics simulations, and (3) collects new QM data whenever the neural network identifies an atomic configuration for which it cannot make a good prediction. All molecular dynamics simulations are initialized to a disordered configuration, and then driven according to randomized, time-varying temperatures. This nonequilibrium molecular dynamics forms a variety of crystalline and defected configurations. By training on all such automatically collected data, we produce ANI-Al, our new interatomic potential for aluminum. We demonstrate the remarkable transferability of ANI-Al by benchmarking against experimental data, e.g., the radial distribution function in melt, various properties of the stable face-centered cubic (FCC) crystal, and the coexistence curve between melt and FCC.
- arXiv:2003.04958 [pdf, other]
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Title: Virial coefficients of trapped and un-trapped three-component fermions with three-body forces in arbitrary spatial dimensionsComments: 7 pages, 2 figuresSubjects: Quantum Gases (cond-mat.quant-gas); Nuclear Theory (nucl-th)
Using a coarse temporal lattice approximation, we calculate the first few terms of the virial expansion of a three-species fermion system with a three-body contact interaction in $d$ spatial dimensions, both in homogeneous space as well as in a harmonic trapping potential of frequency $\omega$. Using the three-body problem to renormalize, we report analytic results for the change in the fourth- and fifth-order virial coefficients $\Delta b_4$ and $\Delta b_5$ as functions of $\Delta b_3$. Additionally, we argue that in the $\omega \to 0$ limit the relationship $b_n^\text{T} = n^{-d/2} b_n$ holds between the trapped (T) and homogeneous coefficients for arbitrary temperature and coupling strength (not merely in scale-invariant regimes). Finally, we point out an exact, universal (coupling- and frequency-independent) relationship between $\Delta b_3^\text{T}$ in 1D with three-body forces and $\Delta b_2^\text{T}$ in 2D with two-body forces.
- arXiv:2003.04995 [pdf, ps, other]
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Title: The Discrete-Time Facilitated Totally Asymmetric Simple Exclusion ProcessComments: 36 pages, 4 figuresSubjects: Mathematical Physics (math-ph); Statistical Mechanics (cond-mat.stat-mech)
We describe the translation invariant stationary states of the one dimensional discrete-time facilitated totally asymmetric simple exclusion process (F-TASEP). In this system a particle at site $j$ in $Z$ jumps, at integer times, to site $j+1$, provided site $j-1$ is occupied and site $j+1$ is empty. This defines a deterministic noninvertible dynamical evolution from any specified initial configuration on $\{0,1\}^{Z}$. When started with a Bernoulli product measure at density $\rho$ the system approaches a stationary state, with phase transitions at $\rho=1/2$ and $\rho=2/3$. We discuss various properties of these states in the different density regimes $0<\rho<1/2$, $1/2<\rho<2/3$, and $2/3<\rho<1$; for example, we show that the pair correlation $g(j)=\langle\eta(i)\eta(i+j)\rangle$ satisfies, for all $n\in Z$, $\sum_{j=kn+1}^{k(n+1)}g(j)=k\rho^2$, with $k=2$ when $0 \le \rho \le 1/2$ and $k=3$ when $2/3 \le \rho \le 1$, and conjecture (on the basis of simulations) that the same identity holds with $k=6$ when $1/2 \le \rho \le 2/3$. The $\rho<1/2$ stationary state referred to above is also the stationary state for the deterministic discrete-time TASEP at density $\rho$ (with Bernoulli initial state) or, after exchange of particles and holes, at density $1-\rho$.
- arXiv:2003.05027 [pdf]
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Title: Chemo-mechanical characterization of hydrated Calcium-Hydrosilicates with coupled Raman and nanoindentation measurementsComments: 32 pages, 8 figuresSubjects: Materials Science (cond-mat.mtrl-sci); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Applied Physics (physics.app-ph)
Celitement is a new type of cement that is based on hydraulic calcium-hydrosilicate (hCHS) that possesses a potential for minimizing the ratio C/S from above 3 in OPC down to 1, which significantly reduces the amount of CO$_2$ released during processing. The reaction kinetics of hCHS differs from that of classical clinker phases due to the presence of highly reactive silicate species, which involve silanol groups instead of pure calcium silicates and aluminates and aluminoferrites. In contrast to Portland cement, no calcium hydroxide is formed during hydration, which otherwise regulates the Ca concentration. Without the buffering role of Ca(OH)$_2$ the concentration of the dissolved species c(Ca$^{2+}$) and c(SiO$_4^{4-}$) and the corresponding pH must be controlled to ensure a reproducible reaction. Pure hCHS reacts isochemically with water, resulting in a C-S-H phase with the same chemical composition as a single hydration product, with a homogeneous distribution of the main elements Ca and Si throughout the sample. Here we study via nanoindentation the mechanical properties of two different types of hardened pastes made out of Celitement (C/S=1.28), with varying amounts of hCHS and variable water to cement ratio. We couple nanoindentation grids with Raman mappings to link the nanoscale mechanical properties to individual microstructural components, yielding in-depth insight into the mechanics of the mineralogical phases constituting the hardened cement paste. We show that we can identify in hardened Celitement paste both fresh C-S-H with varying density, and C-S-H from the raw material using their specific Raman spectra, while simultaneously measuring their mechanical properties. Albeit not suitable for phase identification, EDX measurements provide valuable information about the distribution of alkalis, thus further helping to understand the reaction pattern of hCHS.
- arXiv:2003.05028 [pdf, ps, other]
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Title: Anisotropy and temperature-dependence of spin-orbit torques: Role of magnonsComments: 11 pages, 2 figures, 7 tablesSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci)
We investigate the influence of magnons on the temperature-dependence and the anisotropy of the field-like component of the spin-orbit torque (SOT). For this purpose we use 3rd order perturbation theory in the framework of the Keldysh formalism in order to derive suitable equations to compute the magnonic SOT. We find three contributions to the magnonic field-like SOT, the dependence of which on the relaxation time $\tau$, the spin-wave stiffness $\mathcal{A}$ and the temperature $T$ are given by $T^{3/2}\tau^3 /\mathcal{A}^{3/2}$, $T^{7/2}\tau^5 /\mathcal{A}^{3/2}$ and $T^{5/2}\tau^5/\mathcal{A}^{5/2}$, respectively, if the magnet is effectively three-dimensional. For effectively two-dimensional magnets we find instead $T\tau^3 /\mathcal{A}$, $T^{3}\tau^5 /\mathcal{A}$ and $T^{2}\tau^5/\mathcal{A}^{2}$. Based on this formalism, we compute the magnonic SOT from first principles in Co/Pt(111), O/Co/Pt(111) and Mn/W(001) magnetic bilayers. We find a sizable magnonic SOT, which exhibits a pronounced anisotropy and a strong temperature dependence.
- arXiv:2003.05045 [pdf, other]
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Title: Absence of equilibrium edge currents in theoretical models of topological insulatorsAuthors: Wei ChenComments: 10 pages, 5 figuresJournal-ref: Phys. Rev. B 101, 195120 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
The low energy sector of 2D and 3D topological insulators (TIs) exhibits propagating edge states, which has speculated the existence of equilibrium edge currents or edge spin currents. We demonstrate that if the low energy sector of TIs is regularized in a straightforward manner into a square or cubic lattice, then the current from the edge states is in fact canceled out exactly by that from the valence bands, rendering no edge current. This result serves as a warning that for any equilibrium property of topological insulators, the contribution from the valence bands should not be overlooked. In these regularized lattice model, there is a finite edge current only if the Dirac point of the edge states is shifted away from the chemical potential, for instance by doping, impurities, edge confining potential, surface band bending, or gate voltage. The edge current in small quantum dots as a function of the gate voltage is quantized, and the edge current can flow out of the gated region up to the decay length of the edge state.
- arXiv:2003.05046 [pdf, other]
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Title: Corner accuracy in direct ink writing with support materialSubjects: Applied Physics (physics.app-ph); Soft Condensed Matter (cond-mat.soft)
3D printing methods which enable control over the position and orientation of embedded particles have promising applications in cell patterning and composite scaffolds. Extrusion-based additive manufacturing techniques such as fused deposition modeling and direct ink writing can experience particle patterning defects at corners which could hinder cell survival at corners and create unintended property gradients. Here, we propose models which predict the behavior of deposited lines at corners for moderate viscosity inks which are impacted by both capillarity and viscous dissipation. Using direct ink writing with acoustophoresis and a Carbopol-based support gel, we write polygons out of dental resin-based composite inks containing a narrow distribution of microparticles at the center of the filament. A Laplace pressure differential between the inner and outer surfaces of the corner drives corner smoothing, wherein the inner radius of the corner increases. Double deposition, or printing on the same area twice, drives corner swelling, wherein excess ink is diverted to the outer edge of the corner. Fast turns at corners produce ringing, wherein vibrations in the stage manifest in oscillations in the print path. Swelling and ringing effects are apparent in the particle distributions at corners immediately after deposition, while smoothing effects are apparent after the printed structure has had time to relax. When the nozzle returns to write a neighboring line, it imposes shear stresses which mitigate inconsistencies in microstructure at corners by erasing defects which appeared during relaxation. Using a support bath instead of layer-by-layer support suppresses microstructural corner defects.
- arXiv:2003.05050 [pdf, other]
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Title: Narrow bands and electrostatic interactions in graphene stacksComments: 18 pages, 12 figuresSubjects: Strongly Correlated Electrons (cond-mat.str-el); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Superconductivity (cond-mat.supr-con)
Superconducting and insulating phases are well-established in twisted graphene bilayers, and they have also been reported in other arrangements of graphene layers. We investigate three such situations, (untwisted) bilayer graphene on hBN, two graphene bilayers twisted with respect to each other, and a single ABC stacked graphene trilayer on hBN. In all these cases, narrow bands emerge. The resulting high density of states enhances the role of interactions. We study the effect of the long-range electron-electron interaction on these narrow bands. A self consistent electrostatic potential does not modify significantly the shape and width of the bands in the three cases considered here, in contrast to the effect that such a potential has in twisted bilayer graphene.
- arXiv:2003.05054 [pdf, other]
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Title: Probing chirality with inelastic electron-light scatteringAuthors: Tyler R. Harvey, Jan-Wilke Henke, Ofer Kfir, Hugo Lorenço-Martins, Armin Feist, F. Javier García de Abajo, Claus RopersJournal-ref: Nano Lett. 20 (2020) 4377-4383Subjects: Optics (physics.optics); Materials Science (cond-mat.mtrl-sci)
Circular dichroism spectroscopy is an essential technique for understanding molecular structure and magnetic materials, but spatial resolution is limited by the wavelength of light, and sensitivity sufficient for single-molecule spectroscopy is challenging. We demonstrate that electrons can efficiently measure the interaction between circularly polarized light and chiral materials with deeply sub-wavelength resolution. By scanning a nanometer-sized focused electron beam across an optically-excited chiral nanostructure and measuring the electron energy spectrum at each probe position, we produce a high-spatial-resolution map of near-field dichroism. This technique offers a nanoscale view of a fundamental symmetry and could be employed as "photon staining" to increase biomolecular material contrast in electron microscopy.
- arXiv:2003.05077 [pdf, other]
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Title: Anisotropic three-dimensional weak localization in ultrananocrystalline diamond films with nitrogen inclusionsAuthors: L.H. Willems van Beveren, D.L. Creedon, N. Eikenberg, K. Ganesan, B.C. Johnson, G. Chimowa, D. Churochkin, S. Bhattacharyya, S. PrawerComments: 13 pages, 10 figuresJournal-ref: Phys. Rev. B 101, 115306 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We present a study of the structural and electronic properties of ultra-nanocrystalline diamond films that were modified by adding nitrogen to the gas mixture during chemical vapour deposition growth. Hall bar devices were fabricated from the resulting films to investigate their electrical conduction as a function of both temperature and magnetic field. Through low-temperature magnetoresistance measurements, we present strong evidence that the dominant conduction mechanism in these films can be explained by a combination of 3D weak localization (3DWL) and thermally activated hopping at higher temperatures. An anisotropic 3DWL model is then applied to extract the phase-coherence time as function of temperature, which shows evidence of a power law dependence in good agreement with theory.
- arXiv:2003.05082 [pdf, other]
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Title: Degenerate states, emergent dynamics and fluid mixing by magnetic rotorsSubjects: Soft Condensed Matter (cond-mat.soft); Fluid Dynamics (physics.flu-dyn)
We investigate the collective motion of magnetic rotors suspended in a viscous fluid under an uniform rotating magnetic field. The rotors are positioned on a square lattice, and low Reynolds hydrodynamics is assumed. For a $3 \times 3$ array of magnets, we observe three characteristic dynamical patterns as the external field strength is varied: a synchronized pattern, an oscillating pattern, and a chessboard pattern. The relative stability of these depends on the competition between the energy due to the external magnetic field and the energy of the magnetic dipole-dipole interactions among the rotors. We argue that the chessboard pattern can be understood as an alternation in the stability of two degenerate states, characterized by striped and spin-ice configurations, as the applied magnetic field rotates. For larger arrays, we observe propagation of slip waves that are similar to metachronal waves. The rotor arrays have potential as microfluidic devices that can mix fluids and create vortices of different sizes.
- arXiv:2003.05087 [pdf, other]
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Title: Machine learning in physics: The pitfalls of poisoned training setsComments: 5 pages, 3 figures, 3 tablesSubjects: Disordered Systems and Neural Networks (cond-mat.dis-nn)
Known for their ability to identify hidden patterns in data, artificial neural networks are among the most powerful machine learning tools. Most notably, neural networks have played a central role in identifying states of matter and phase transitions across condensed matter physics. To date, most studies have focused on systems where different phases of matter and their phase transitions are known, and thus the performance of neural networks is well controlled. While neural networks present an exciting new tool to detect new phases of matter, here we demonstrate that when the training sets are poisoned (i.e., poor training data or mislabeled data) it is easy for neural networks to make misleading predictions.
- arXiv:2003.05098 [pdf, other]
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Title: Landau poles in condensed matter systemsComments: 17 pages, 5 figuresJournal-ref: Phys. Rev. Research 2, 023310 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el); High Energy Physics - Lattice (hep-lat); High Energy Physics - Theory (hep-th)
The existence or not of Landau poles is one of the oldest open questions in non-asymptotic quantum field theories. We investigate the Landau pole issue in two condensed matter systems whose long-wavelength physics is described by appropriate quantum field theories: the critical quantum magnet and Dirac fermions in graphene with long-range Coulomb interactions. The critical quantum magnet provides a classic example of a quantum phase transition, and it is well described by the $\phi^4$ theory. We find that the irrelevant but symmetry-allowed couplings, such as the $\phi^6$ potential, can significantly change the fate of the Landau pole in the $\phi^4$ theory. We obtain the coupled beta functions of a $\phi^4 + \phi^6$ potential at both small and large orders. Already from the 1-loop calculation, the Landau pole is replaced by an ultraviolet fixed point. A Lipatov analysis at large orders reveals that the inclusion of a $\phi^6$ term also has important repercussions for the high-order expansion of the beta functions. We also investigate the role of the Landau pole in 2+1 dimensional Dirac fermions with Coulomb interactions, e.g., graphene. Both the weak-coupling perturbation theory up to 2 loops and a low-order large-N calculation show the absence of a Landau pole. Furthermore, we calculate the asymptotic expansion coefficients of the beta function. We find that the asymptotic coefficient is bounded by that of a $\phi^4$ theory, so graphene is free from Landau poles if the $\phi^4$ theory does not manifest a Landau pole. We briefly discuss possible experiments that could potentially probe the existence of a Landau pole in these systems. Studying Landau poles in suitable condensed matter systems is of considerable fundamental importance since the relevant Landau pole energy scales in particle physics, whether it is quantum electrodynamics or Higgs physics, are completely unattainable.
- arXiv:2003.05099 [pdf, ps, other]
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Title: Fast forward approach to stochastic heat engineComments: 14 pages, 3 figuresSubjects: Statistical Mechanics (cond-mat.stat-mech)
The fast-forward (FF) scheme proposed by Masuda and Nakamura (\textit{Proc. R. Soc. A} \textbf{466}, 1135 (2010)) in the context of conservative quantum dynamics can reproduce a quasi-static dynamics in an arbitrarily short time. We apply the FF scheme to the classical stochastic Carnot-like heat engine which is driven by a Brownian particle coupled with a time-dependent harmonic potential and working between the high ($T_h$)- and low ($T_c$)-temperature heat reservoirs. Concentrating on the underdamped case where momentum degree of freedom is included, we find the explicit expressions for the FF protocols necessary to accelerate both the isothermal and thermally-adiabatic processes, and obtain the reversible and irreversible works. The irreversible work is shown to consist of two terms with one proportional to and the other inversely proportional to the friction coefficient. The optimal value of efficiency $\eta$ at the maximum power of this engine is found to be universal and given by $\eta^*=\frac{1}{2} \left(1+\frac{1}{2}\left(\frac{T_c}{T_h}\right)^{\frac{1}{2}} - \frac{5}{4}\frac{T_c}{T_h} +O\left(\left(\frac{T_c}{T_h}\right)^{\frac{3}{2}}\right)\right)$ and $\eta^*= 1- \frac{1}{2} \left(\frac{T_c}{T_h}\right)^{\frac{1}{2}}$, respectively in the cases of strong and weak dissipation. The result is justified for a wide family of time scaling functions, making the FF protocols very flexible. The FF scheme applied to the overdamped case sweeps out a mist hanging over the treatment of thermally-adiabatic process.
- arXiv:2003.05125 [pdf]
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Title: Single-Carrier Transport in Graphene/hBN SuperlatticesAuthors: Takuya Iwasaki, Shu Nakaharai, Yutaka Wakayama, Kenji Watanabe, Takashi Taniguchi, Yoshifumi Morita, Satoshi MoriyamaJournal-ref: Nano Lett. 20, 2551-2557 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Graphene/hexagonal boron nitride (hBN) moir\'e superlattices have attracted interest for use in the study of many-body effects and fractal physics in Dirac fermion systems. Many exotic transport properties have been intensively examined in such superlattices, but previous studies have not focused on single-carrier transport. The investigation of the single-carrier behavior in these superlattices would lead to an understanding of the transition of single-particle/correlated phenomena. Here, we show the single-carrier transport in a high-quality bilayer graphene/hBN superlattice-based quantum dot device. We demonstrate remarkable device controllability in the energy range near the charge neutrality point (CNP) and the hole-side satellite point. Under a perpendicular magnetic field, Coulomb oscillations disappear near the CNP, which could be a signature of the crossover between Coulomb blockade and quantum Hall regimes. Our results pave the way for exploring the relationship of single-electron transport and fractal quantum Hall effects with correlated phenomena in two-dimensional quantum materials.
- arXiv:2003.05132 [pdf, other]
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Title: SIMBA: A Skyrmionic In-Memory Binary Neural Network AcceleratorSubjects: Emerging Technologies (cs.ET); Disordered Systems and Neural Networks (cond-mat.dis-nn)
Magnetic skyrmions are emerging as potential candidates for next generation non-volatile memories. In this paper, we propose an in-memory binary neural network (BNN) accelerator based on the non-volatile skyrmionic memory, which we call as SIMBA. SIMBA consumes 26.7 mJ of energy and 2.7 ms of latency when running an inference on a VGG-like BNN. Furthermore, we demonstrate improvements in the performance of SIMBA by optimizing material parameters such as saturation magnetization, anisotropic energy and damping ratio. Finally, we show that the inference accuracy of BNNs is robust against the possible stochastic behavior of SIMBA (88.5% +/- 1%).
- arXiv:2003.05147 [pdf, other]
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Title: Collapse of the vacuum in hexagonal graphene quantum dots: a comparative study between the tight-binding and the mean-field Hubbard modelsSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
In this paper, we perform a systematic study on the electronic, magnetic, and transport properties of the hexagonal graphene quantum dots (GQDs) with armchair edges in the presence of a charged impurity using two different configurations: (1) a central Coulomb potential and (2) a positively charged carbon vacancy. The tight binding (TB) and the half-filled extended Hubbard models are numerically solved and compared with each other in order to reveal the effect of electron interactions and system sizes. Numerical results point out that off-site Coulomb repulsion leads to an increase in the critical coupling constant to $\beta_{\text{c}}$ = 0.6 for a central Coulomb potential. This critical value of the $\beta$ is found to be independent of GQD size, reflecting its universality even in the presence of electron-electron interactions. In addition, a sudden downshift in the transmission peaks shows a clear signature of the transition from subcritical $\beta$ $<$ $\beta_{\text{c}}$ to supercritical $\beta$ $>$ $\beta_{\text{c}}$ regime. On the other hand, for a positively charged vacancy, the collapse of the lowest bound state occurs at $\beta_{\text{c}}$ = 0.7 for the interacting case. Interestingly, the local magnetic moment, induced by a bare carbon vacancy, is totally quenched when the vacancy is subcritically charged, whereas the valley splittings in electron and hole channels continue to exist in both regimes.
- arXiv:2003.05149 [pdf, ps, other]
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Title: Creation and manipulation of quantized vortices in Bose-Einstein condensates using reinforcement learningAuthors: Hiroki SaitoComments: 7 pages, 5 figures, 2 moviesSubjects: Quantum Gases (cond-mat.quant-gas); Disordered Systems and Neural Networks (cond-mat.dis-nn)
We apply the technique of reinforcement learning to the control of nonlinear matter waves. In this method, an agent controls the position, strength, and shape of an external Gaussian potential to create and manipulate quantized vortices in a Bose-Einstein condensate (BEC) trapped in a harmonic potential. The density and velocity distributions of the BEC at each moment obtained by the Gross-Pitaevskii evolution are directly input into a convolutional neural network to determine the next action of the agent. We demonstrate that a stationary single-vortex state can be produced in a two-dimensional system, and a stationary vortex-ring state can be produced in a three-dimensional system.
- arXiv:2003.05159 [pdf, other]
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Title: Excitation and relaxation dynamics of spin-waves triggered by ultrafast photo-induced demagnetization in a ferrimagnetic insulatorComments: 7 pages, 4 figuresSubjects: Materials Science (cond-mat.mtrl-sci); Applied Physics (physics.app-ph); Optics (physics.optics)
Excitation and propagation dynamics of spin waves in an iron-based garnet film under out-of-plane magnetic field were investigated by time-resolved magneto-optical imaging. The experimental results and the following data analysis by phase-resolved spin-wave tomography reveal the excitation of spin waves triggered by photo-induced demagnetization (PID) along the sample depth direction. Moreover, the fast relaxation of PID accompanied by the spin transfer due to spin-wave emission was observed. Possible scenarios of PID in the garnet film are discussed. Finally, we develop a model for the spin-wave excitation triggered by PID and explain the magnetic-field dependence in the amplitude of the observed spin waves.
- arXiv:2003.05163 [pdf, other]
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Title: Correlations in the elastic Landau level of a graphene/NbSe$_2$ van der Waals heterostructureAuthors: Antonio L. R. Manesco, Jose L. Lado, Eduardo V. Ribeiro, Gabrielle Weber, Durval Rodrigues JrComments: 6 pages, 5 figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Electronic correlations stemming from nearly flat bands in van der Waals materials have demonstrated to be a powerful playground to engineer artificial quantum matter, including superconductors, correlated insulators and topological matter. This phenomenology has been experimentally observed in a variety of twisted van der Waals materials, such as graphene and dichalcogenide multilayers. Here we show that a hybrid graphene/dichalcogenide multilayer can yield a correlated state, emerging from an elastic pseudo Landau level. Our results build on top of recent experimental findings reporting that, when placed on top of a NbSe$_2$ substrate, graphene sheets relax forming a periodic, long-range buckling pattern caused by the lattice mismatch. The low-energy physics can be accurately described by electrons in the presence of a pseudo-axial gauge field, leading to the formation of sublattice-polarized Landau levels. Moreover, we verify that the high density of states at the zeroth Landau level leads to the formation of a periodically modulated ferrimagnetic groundstate, which can be controlled by the application of external electric fields. Our results indicate that van der Waals heterostructures combining graphene and dichalcogenides are a versatile platform to explore emergent electronic states arising from correlated elastic Landau levels.
- arXiv:2003.05170 [pdf, other]
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Title: Topological Theory for Perfect Metasurface IsolatorsComments: 5 pages, 4 figuresJournal-ref: Phys Rev B (Rapid Comm) 101, 121405(R) (2020)Subjects: Optics (physics.optics); Other Condensed Matter (cond-mat.other)
We introduce topological theory of perfect isolation: perfect transmission from one side and total reflection from another side simultaneously. The theory provides an efficient approach for determining whether such a perfect isolation point exists within a finite parameter space. Herein, we demonstrate the theory using an example of a Lorentz non-reciprocal metasurface composed of dimer unit cells. Our theory also suggests that perfect isolation points can annihilate each other through the coalescence of opposite topological charges. Our findings could lead to novel designs for high-performance optical isolators.
- arXiv:2003.05181 [pdf, other]
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Title: Time-induced second-order topological superconductorsAuthors: Raditya Weda BomantaraComments: 11 pages, 6 figures, comments are welcomeSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Quantum Physics (quant-ph)
Higher-order topological materials, characterized by the presence of topologically protected states at the boundaries of their boundaries (hinges or corners), have attracted attention in recent years. In this paper, we propose a means to transform an inherently trivial system into a second-order topological superconductor by introducing nontrivial winding of a quasimomentum in the time-domain. Unlike other proposals of Floquet second-order topological phases developed in recent years, the generation of Majorana corner modes in our scheme arises from the interplay of topology in both spatial and temporal dimensions, where the underlying static system lacks the mechanism to ever host them. Our scheme thus brings forward the idea of Floquet engineering to another level where periodic drive can itself be endowed with topology to potentially reduce the complexity of the underlying static systems for hosting exotic topological phases.
- arXiv:2003.05202 [pdf, other]
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Title: Nematic superconductivity in topological insulators induced by hexagonal warpingComments: 5 pages, 4 figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Superconductivity (cond-mat.supr-con)
We study superconducting properties of the bulk states of a doped topological insulator. We obtain that the hexagonal warping stabilizes the nematic spin-triplet superconducting phase with $E_u$ pairing. The nematic order parameter opens a full gap in the electron spectrum. This order parameter exhibits non-BCS behavior. In particular, the order parameter scales with temperature as $\sqrt{1-\left(T/T_c\right)^3}$. It depends on the chemical potential, that is, doping and on the value of the hexagonal warping. We discus a relevance of the obtained results for the explanation of the experimental observations.
- arXiv:2003.05215 [pdf, other]
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Title: Real-space cluster dynamical mean-field theory: Center focused extrapolation on the one- and two particle levelAuthors: Marcel Klett, Nils Wentzell, Thomas Schäfer, Fedor Simkovic IV, Olivier Parcollet, Sabine Andergassen, Philipp HansmannComments: 11 pages, 13 figuresSubjects: Strongly Correlated Electrons (cond-mat.str-el)
We revisit the cellular dynamical mean-field theory (CDMFT) for the single band Hubbard model on the square lattice at half filling, reaching real-space cluster sizes of up to 9 x 9 sites. Using benchmarks against direct lattice diagrammatic Monte Carlo at high temperature, we show that the self-energy obtained from a cluster center focused extrapolation converges faster with the cluster size than the periodization schemes previously introduced in the literature. The same benchmark also shows that the cluster spin susceptibility can be extrapolated to the exact result at large cluster size, even though its spatial extension is larger than the cluster size.
- arXiv:2003.05231 [pdf, other]
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Title: Quantum droplets in one-dimensional Bose mixtures: a quantum Monte-Carlo studySubjects: Quantum Gases (cond-mat.quant-gas)
We use exact Quantum Monte Carlo techniques to study the properties of quantum droplets in two-component bosonic mixtures with contact interactions in one spatial dimension. We systematically study the surface tension, the density profile and the breathing mode as a function of the number of particles in the droplet and of the ratio of coupling strengths between intra-species repulsion and inter-species attraction. We find that deviations from the predictions of the generalized Gross-Pitaevskii equation are small in most cases of interest.
- arXiv:2003.05232 [pdf, other]
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Title: Spin Seebeck Effect near the Antiferromagnetic Spin-Flop TransitionComments: 5 pages, 3 figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We develop a low-temperature, long-wavelength theory for the interfacial spin Seebeck effect (SSE) in easy-axis antiferromagnets. The field-induced spin-flop (SF) transition of N\'eel order is associated with a qualitative change in SSE behavior: Below SF, there are two spin carriers with opposite magnetic moments, with the carriers polarized along the field forming a majority magnon band. Above SF, the low-energy, ferromagnetic-like mode has magnetic moment opposite the field. This results in a sign change of the SSE across SF, which agrees with recent measurements on Cr$_2$O$_3$/Pt and Cr$_2$O$_3$/Ta devices [Li $\textit{et al.,}$ $\textit{Nature}$ $\textbf{578,}$ 70 (2020)]. In our theory, SSE is due to a N\'eel spin current below SF and a magnetic spin current above SF. Using the ratio of the associated N\'eel to magnetic spin-mixing conductances as a single constant fitting parameter, we reproduce the field dependence of the experimental data and partially the temperature dependence of the relative SSE jump across SF.
- arXiv:2003.05248 [pdf, other]
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Title: Three-dimensional needle network model for dendritic growth with fluid flowSubjects: Computational Physics (physics.comp-ph); Materials Science (cond-mat.mtrl-sci)
We present a first implementation of the Dendritic Needle Network (DNN) model for dendritic crystal growth in three dimensions including convective transport in the melt. The numerical solving of the Navier-Stokes equations is performed with finite differences and is validated by comparison with a classical benchmark in fluid mechanics for unsteady flow. We compute the growth behavior of a single equiaxed crystal under a forced convective flow. As expected, the resulting dendrite morphology differs strongly from the case of the purely diffusive regime and from similar two-dimensional simulations. The resulting computationally efficient simulations open the way to studying mechanisms of microstructure selection in presence of fluid flow, using realistic alloys and process parameters.
- arXiv:2003.05250 [pdf, other]
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Title: Comparing mesoscopic models for dendritic growthSubjects: Computational Physics (physics.comp-ph); Materials Science (cond-mat.mtrl-sci)
We present a quantitative benchmark of multiscale models for dendritic growth simulations. We focus on approaches based on phase-field, dendritic needle network, and grain envelope dynamics. As a first step, we focus on isothermal growth of an equiaxed grain in a supersaturated liquid in three dimensions. A quantitative phase-field formulation for solidification of a dilute binary alloy is used as the reference benchmark. We study the effect of numerical and modeling parameters in both needle-based and envelope-based approaches, in terms of their capacity to quantitatively reproduce phase-field reference results. In light of this benchmark, we discuss the capabilities and limitations of each approach in quantitatively and efficiently predicting transient and steady states of dendritic growth. We identify parameters that yield a good compromise between accuracy and computational efficiency in both needle-based and envelope-based models. We expect that these results will guide further developments and utilization of these models, and ultimately pave the way to a quantitative bridging of the dendrite tip scale with that of entire experiments and solidification processes.
- arXiv:2003.05274 [pdf, other]
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Title: Efficient large deviation estimation based on importance samplingComments: 34 pages, 8 figuresSubjects: Statistical Mechanics (cond-mat.stat-mech); Probability (math.PR)
We present a complete framework for determining the asymptotic (or logarithmic) efficiency of estimators of large deviation probabilities and rate functions based on importance sampling. The framework relies on the idea that importance sampling in that context is fully characterized by the joint large deviations of two random variables: the observable defining the large deviation probability of interest and the likelihood factor (or Radon-Nikodym derivative) connecting the original and modified process used in importance sampling. We recover with this framework known results about the asymptotic efficiency of the exponential tilting and obtain new necessary and sufficient conditions for a general change of process to be asymptotically efficient. This allows us to construct new examples of efficient estimators for sample means of random variables that do not have the exponential tilting form. Other examples involving Markov chains and diffusions are presented to illustrate our results.
- arXiv:2003.05284 [pdf]
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Title: Tailored pore gradient in phenolic membranes for adjustable permselectivity by leveraging different poloxamersJournal-ref: Sep. Purif. Technol. 242 (2020) 116818Subjects: Applied Physics (physics.app-ph); Materials Science (cond-mat.mtrl-sci)
Cost-affordable phenolic membranes having gradient nanostructures can be facilely synthesized from resol oligomers in the presence of ZnCl2 and poloxamers. The gradient nanostructures are formed by stacking phenolic nanoparticles with gradually enlarged diameters as the distance from the upper surface increases. The use of poloxamers for creating gelation surroundings is of great significance for controlling the growth of phenolic nanoparticles, which in turn dictates the performance of the phenolic membranes thus-produced. Hence, a study of the effects of poloxamers species on the preparation of the phenolic membranes is highly demanded since such robust membranes have much potential to be scale up for mass production. Herein, the poloxamer Pluronic F127 (EO106-PO70-EO106; EO = ethyleneoxide, PO = propyleneoxide) was introduced in the membrane-forming formulations. As opposed to P123 (EO20-PO70-EO20) that we used previously, F127 possessing extended PEO chains can delay the gelation during membrane formation. Hence, the phenolic nucleates are able to grow for longer durations, leading to the generation of more distinct gradient nanostructures in the phenolic membranes. Enhanced permeance can then be realized with F127-derived phenolic membranes. We also demonstrate that L31 (EO1-PO22-EO1) with merely single terminal EO units at the ends of the PPO block could be used to prepare gradient phenolic membranes. This work is not only much helpful to deeply understand the design of the structural gradient in phenolic membranes, but capable of sheding light on the development of such intriguing structures for water purification.
- arXiv:2003.05288 [pdf, ps, other]
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Title: The Brownian Motion in an Ideal Quantum QasSubjects: Statistical Mechanics (cond-mat.stat-mech)
A Brownian particle in an ideal quantum gas is considered. The mean square displacement (MSD) is derived. The Bose-Einstein or Fermi-Dirac distribution, other than the Maxwell-Boltzmann distribution, provides a different stochastic force compared with the classical Brownian motion. The MSD, which depends on the thermal wavelength and the density of medium particles, reflects the quantum effect on the Brownian particle explicitly. The result shows that the MSD in an ideal Bose gas is shorter than that in a Fermi gas. The behavior of the quantum Brownian particle recovers the classical Brownian particle as the temperature raises. At low temperatures, the quantum effect becomes obvious. For example, there is a random motion of the Brownian particle due to the fermionic exchange interaction even the temperature is near the absolute zero.
- arXiv:2003.05297 [pdf, other]
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Title: Microscopic origin of molecule excitation via inelastic electron scattering in scanning tunneling microscopeSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Quantum Physics (quant-ph)
The scanning-tunneling-microscope-induced luminescence emerges recently as an incisive tool to measure the molecular properties down to the single-molecule level. The rapid experimental progress is far ahead of the theoretical effort to understand the observed phenomena. Such incompetence leads to a significant difficulty in quantitatively assigning the observed feature of the fluorescence spectrum to the structure and dynamics of a single molecule. This letter is devoted to reveal the microscopic origin of the molecular excitation via inelastic scattering of the tunneling electrons in scanning tunneling microscope. The current theory explains the observed large photon counting asymmetry between the molecular luminescence intensity at positive and negative bias voltage.
- arXiv:2003.05301 [pdf, other]
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Title: Signatures of Hundness in Kagome MetalsComments: 5 pages, 3 figuresSubjects: Strongly Correlated Electrons (cond-mat.str-el); Materials Science (cond-mat.mtrl-sci)
By means of the density functional theory in combination with the dynamical mean-field theory, we tried to examine the electronic structure of hexagonal FeGe, in which the Fe atoms form a quasi-2D layered Kagome lattice. We predict that it is a representative Kagome metal characterized by orbital selective Dirac fermions and extremely flat bands. Furthermore, Fe's 3$d$ electrons are strongly correlated. They exhibit quite apparent signatures of electronic correlation induced by Hund's rule coupling, such as sizable differentiation in band renormalization, non-Fermi-liquid behavior, spin-freezing state, and spin-orbital separation. Thus, FeGe can be regarded as an ideal platform to study the interplay of Kagome physics and Hundness. 5
- arXiv:2003.05304 [pdf, other]
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Title: Quantizing Lévy FlightsComments: 5 pages main text, 2 figures 13 pages Sup. Mat., 1 figureSubjects: Statistical Mechanics (cond-mat.stat-mech); Other Condensed Matter (cond-mat.other)
The Caldeira-Leggett model of quantum Brownian motion is generalized using a generic velocity-dependent coupling. A Langevin equation with memory and multiplicative noise is derived. Through path-integral quantization in Euclidean time, the environment is integrated out, leaving a set of non-local effective actions. A coupling force is found, which establishes a connection with L\'evy flights of cold atoms in Sisyphus laser cooling. In the low-velocity limit, this also gives rise to additional inertia of the Brownian particle, resisting acceleration. These results further serve as starting points for several numerical calculations, particularly decoherence properties of non-ohmic baths.
- arXiv:2003.05305 [pdf, other]
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Title: Abrupt transition between three and two-dimensional quantum turbulenceJournal-ref: Physical Review Letters 124, 134501 (2020)Subjects: Quantum Gases (cond-mat.quant-gas); Fluid Dynamics (physics.flu-dyn)
We present numerical evidence of a critical-like transition in an out-of-equilibrium mean-field description of a quantum system. By numerically solving the Gross-Pitaevskii equation we show that quantum turbulence displays an abrupt change between three-dimensional (3D) and two-dimensional (2D) behavior. The transition is observed both in quasi-2D flows in cubic domains (controlled by the amplitude of a 3D perturbation to the flow), as well as in flows in thin domains (controlled by the domain aspect ratio) in a configuration that mimics systems realized in laboratory experiments. In one regime the system displays a transfer of the energy towards smaller scales, while in the other the system displays a transfer of the energy towards larger scales and a coherent self-organization of the quantized vortices.
- arXiv:2003.05316 [pdf, other]
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Title: Pseudo-field effects in type II semimetals: new probes for over-tilted Weyl conesComments: 11 pages, 8 figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci)
We study the effects of pseudo-magnetic fields on Weyl semimetals with over-tilted Weyl cones, or type II cones. We compare the phenomenology of the resulting pseudo-Landau levels in the type II Weyl semimetal to the known case of type I cones. We predict that due to the nature of the chiral Landau level resulting from a magnetic field, a pseudo-magnetic field, or their combination, the optical conductivity can be utilized to detect a type II phase and deduce the direction of the tilt. Finally, we discuss ways to engineer homogeneous and inhomogeneous type II semimetals via generalizations of known layered constructions in order to create controlled pseudo-magnetic fields and over-tilted cones.
- arXiv:2003.05319 [pdf, other]
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Title: Photo-induced electron pairing in a driven cavitySubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We demonstrate how virtual scattering of laser photons inside a cavity via two-photon processes can induce controllable long-range electron interactions in two-dimensional materials. We show that laser light that is red(blue)-detuned from the cavity yields attractive(repulsive) interactions, whose strength is proportional to the laser intensity. Furthermore, we find that the interactions are not screened effectively except at very low frequencies. For realistic cavity parameters, laser-induced heating of the electrons by inelastic photon scattering is suppressed and coherent electron interactions dominate. When the interactions are attractive, they cause an instability in the Cooper channel at a temperature proportional to the square root of the driving intensity. Our results provide a novel route for engineering electron interactions in a wide range of two-dimensional materials including AB-stacked bilayer graphene and the conducting interface between LaAlO3 and SrTiO3.
- arXiv:2003.05343 [pdf, other]
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Title: Temporally resolved LEIS measurements of Cr segregation after preferential sputtering of WCrY alloyComments: 20 pages, 4 figures, Proceedings of the 23rd International Workshop on Inelastic Ion-Surface Collisions (IISC-23), submitted to Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and AtomsSubjects: Materials Science (cond-mat.mtrl-sci)
The dynamic behaviour of thermally driven segregation of Cr to the surface of WCrY smart alloy is studied with low energy ion scattering (LEIS). Sputtering the WCrY sample with 500 eV D$_2^+$ ions at room temperature results in preferential removal of the lighter alloy constituents and causes an almost pure W surface layer. At elevated temperatures above 700 K the segregation of Cr atoms towards the surface sets in and prevents the formation of a pure W layer. The simultaneous heating and sputtering of the sample leads to a surface state which reflects the balance between sputter removal and segregation flux, and deviates from the equilibrium due to thermally driven segregation. Stopping the sputter ion beam allows the system to relax and develop toward the segregation equilibrium. The time constants for the temporal changes of W and Cr surface coverage are obtained from a series of LEIS measurements. The segregation enthalpy is determined from the time constants obtained for various sample temperatures.
- arXiv:2003.05346 [pdf]
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Title: Gate tuning and universality of Two-stage Kondo effect in single molecule transistorsComments: 4 figures, 10 pages for main text. 5 figures 11pages as supplementarySubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Using single molecule transistor incorporating individual Manganese phthalocynine (MnPc) molecules, we studied two-stage Kondo effect involving a multi-level impurity. Utilizing extreme confined molecular structure, we have achieved gate tuning of Kondo temperatures for single channel two-stage Kondo process. Single gate in our devices can significantly change the Kondo temperature T* representing the internal correlation between different molecular levels. A linear relationship was obtained between the T* and effective interaction of two electrons, and exchange energy of electrons in this molecule device could be extracted accordingly. Moreover, the two-stage Kondo resonance behaves almost identical to small excitations in electric field, magnetic field and thermal change, showing a clear universality. Messages learned in this study not only fill in missing experimental knowledge of evolution in two-stage Kondo resonance toward the quantum phase transition point, but also help in understanding sophisticated molecular electronic spectroscopy in strong correlation regime.
- arXiv:2003.05350 [pdf, ps, other]
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Title: Cell cycle heritability and localization phase transition in growing populationsSubjects: Populations and Evolution (q-bio.PE); Statistical Mechanics (cond-mat.stat-mech); Biological Physics (physics.bio-ph)
The cell cycle duration is a variable cellular phenotype that underlies long-term population growth and age structures. By analyzing the stationary solutions of a branching process with heritable cell division times, we demonstrate existence of a phase transition, which can be continuous or first-order, by which a non-zero fraction of the population becomes localized at a minimal division time. Just below the transition, we demonstrate coexistence of localized and delocalized age-structure phases, and power law decay of correlation functions. Above it, we observe self-synchronization of cell cycles, collective divisions, and slow 'aging' of population growth rates.
- arXiv:2003.05369 [pdf, ps, other]
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Title: Thermally Tunable Surface Acoustic Wave CavitiesAuthors: André Luiz Oliveira Bilobran, Alberto García-Cristóbal, Paulo Ventura dos Santos, Andrés Cantarero, Mauricio Morais de Lima JrSubjects: Applied Physics (physics.app-ph); Materials Science (cond-mat.mtrl-sci)
We experimentally demonstrate the dynamical tuning of the acoustic field in a surface acoustic wave (SAW) cavity defined by a periodic arrangement of metal stripes on LiNbO3 substrate. Applying a DC voltage to the ends of the metal grid results in a temperature rise due to resistive heating that changes the frequency response of the device up to 0.3%, which can be used to control the acoustic transmission through the structure. The time scale of the switching is demonstrated to be of about 200 ms. In addition, we have also performed finite element simulations of the transmission spectrum of a model system which exhibit a temperature dependence consistent with the experimental data. The advances shown here enable easy, continuous, dynamical control and could be applied for a variety of substrates.
- arXiv:2003.05373 [pdf, other]
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Title: Lattice modulation spectroscopy of one-dimensional quantum gases:Universal scaling of the absorbed energyComments: RevTeX 4, 15 pages, 2 PDF figuresSubjects: Quantum Gases (cond-mat.quant-gas); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Lattice modulation spectroscopy is a powerful tool for probing low-energy excitations of interacting many-body systems. By means of bosonization we analyze the absorbed power in a one dimensional interacting quantum gas of bosons or fermions, subjected to a periodic drive of the optical lattice. For these Tomonaga Luttinger liquids we find a universal $\omega^3$ scaling of the absorbed power, that at very low-frequency turns into an $\omega^2$ scaling when scattering processes at the boundary of the system are taken into account. We confirm this behavior numerically by simulations based on time-dependent matrix product states. Furthermore, in the presence of impurities, the theory predicts an $\omega^2$ bulk scaling. While typical response functions of Tomonaga Luttinger liquids are characterized by exponents that depend on the interaction strength, modulation spectroscopy of cold atoms leads to a universal powerlaw exponent of the absorbed power. Our findings can be readily demonstrated in ultracold atoms in optical lattices with current experimental technology.
- arXiv:2003.05394 [pdf, ps, other]
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Title: Comment on "Low-frequency lattice phonons in halide perovskites explain high defect tolerance toward electron-hole recombination"Comments: 3 pages, 1 tableSubjects: Materials Science (cond-mat.mtrl-sci)
Halide perovskites exhibit slow rates of non-radiative electron-hole recombination upon illumination. Chu et al. [Sci. Adv. 6 7, eaaw7453 (2020)] use the results of first-principles simulations to argue that this arises from the nature of the crystal vibrations and leads to a breakdown of Shockley-Read-Hall theory. We highlight flaws in their methodology and analysis of carrier capture by point defects in crystalline semiconductors.
- arXiv:2003.05398 [pdf, other]
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Title: Stratification of polymer-colloid mixtures via fast nonequilibrium evaporationComments: 12 pages, 12 figures (5 pages, 6 figures for Supplemental Material)Subjects: Soft Condensed Matter (cond-mat.soft)
In drying liquid films of polymer-colloid mixtures, the stratification in which polymers are placed on top of larger colloids is studied. It is often presumed that the formation of segregated polymer-colloid layers is solely due to the proportion in size at fast evaporation as in binary colloid mixtures. By comparing experiments with a theoretical model, we found that the transition in viscosity near the drying interface was another important parameter for controlling the formation of stratified layers in polymer-colloid mixtures. At high evaporation rates, increased polymer concentrations near the surface lead to a phase transition from semidilute to concentrated regime, in which colloidal particles are kinetically arrested. Stratification only occurs if the formation of a stratified layer precedes the evolution to the concentrated regime near the drying interfaces. Otherwise, the colloids will be trapped by the polymers in the concentrated regime before forming a segregated layer. Also, no stratification is observed if the initial polymer concentration is too low to form a sufficiently high polymer concentration gradient within a short period of time. Our findings are relevant for developing solution-cast polymer composite for painting, antifouling and antireflective coatings.
- arXiv:2003.05401 [pdf, other]
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Title: Correlated Disorder in the SYK$_{2}$ modelComments: 27 pages, 13 figures, minor changes, reference addedSubjects: High Energy Physics - Theory (hep-th); Statistical Mechanics (cond-mat.stat-mech); Quantum Physics (quant-ph)
We study the SYK$_{2}$ model of $N$ Majorana fermions with random quadratic interactions through a detailed spectral analysis and by coupling the model to 2- and 4-point sources. In particular, we define the generalized spectral form factor and level spacing distribution function by generalizing from the partition function to the generating function. For $N=2$, we obtain an exact solution of the generalized spectral form factor. It exhibits qualitatively similar behavior to the higher $N$ case with a source term, this exact solution helps to understand the behavior of the generalized spectral form factor. We calculate the generalized level spacing distribution function and the mean value of the adjacent gap ratio defined by the generating function. We find a Gaussian unitary ensemble for the SYK$_2$ model with a 4-point source term in a near-integrable region of the theory indicating a transition to chaos. This chaotic property might be expected to be more evident with stronger source terms. On the contrary, we find a departure from random matrix behavior as the source term is enhanced.
- arXiv:2003.05414 [pdf, other]
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Title: Planar Josephson Hall effect in topological Josephson junctionsComments: 16 pages, 6 figures, fixed referencesSubjects: Superconductivity (cond-mat.supr-con); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Josephson junctions based on three-dimensional topological insulators offer intriguing possibilities to realize unconventional $p$-wave pairing and Majorana modes. Here, we provide a detailed study of the effect of a uniform magnetization in the normal region: We show how the interplay between the spin-momentum locking of the topological insulator and an in-plane magnetization parallel to the direction of phase bias leads to an asymmetry of the Andreev spectrum with respect to transverse momenta. If sufficiently large, this asymmetry induces a transition from a regime of gapless, counterpropagating Majorana modes to a regime with unprotected modes that are unidirectional at small transverse momenta. Intriguingly, the magnetization-induced asymmetry of the Andreev spectrum also gives rise to a Josephson Hall effect, that is, the appearance of a transverse Josephson current. The amplitude and current phase relation of the Josephson Hall current are studied in detail. In particular, we show how magnetic control and gating of the normal region can enable sizable Josephson Hall currents compared to the longitudinal Josephson current. Finally, we also propose in-plane magnetic fields as an alternative to the magnetization in the normal region and discuss how the planar Josephson Hall effect could be observed in experiments.
- arXiv:2003.05415 [pdf, other]
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Title: Impact of Aliovalent Alkaline-Earth Metal Solutes on Ceria Grain Boundaries: A Density Functional Theory StudyComments: 23 pages, 4 figuresSubjects: Materials Science (cond-mat.mtrl-sci)
Ceria has proven to be an excellent ion-transport and ion-exchange material when used in polycrystalline form and with a high-concentration of aliovalent doped cations. Despite its widespread application, the impact of atomic-scale defects in this material are scarcely studied and poorly understood. In this article, using first-principles simulations, we provide a fundamental understanding of the atomic-structure, thermodynamic stability and electronic properties of undoped grain-boundaries (GBs) and alkaline-earth metal (AEM) doped GBs in ceria. Using density-functional theory simulations, with a GGA+U functional, we find the $\Sigma$3 (111)/[$\bar{1}$01] GB is thermodynamically more stable than the $\Sigma$3 (121)/[$\bar{1}$01] GB due to the larger atomic coherency in the $\Sigma$3 (111)/[$\bar{1}$01] GB plane. We dope the GBs with $\sim$20% [M]$_{GB}$ (M=Be, Mg, Ca, Sr, and Ba) and find that the GB energies have a parabolic dependence on the size of solutes, the interfacial strain and the packing density of the GB. We see a stabilization of the GBs upon Ca, Sr and Ba doping whereas Be and Mg render them thermodynamically unstable. The electronic density of states reveal that no defect states are present in or above the band gap of the AEM doped ceria, which is highly conducive to maintain low electronic mobility in this ionic conductor. The electronic properties, unlike the thermodynamic stability, exhibit complex inter-dependence on the structure and chemistry of the host and the solutes. This work makes advances in the atomic-scale understanding of aliovalent cation doped ceria GBs serving as an anchor to future studies that can focus on understanding and improving ionic-transport.
- arXiv:2003.05423 [pdf, other]
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Title: Disjoining pressure oscillations causing height discretization in graphene nanobubblesAuthors: Timur Aslyamov, Ekaterina Khestanova, Maria Korneva, Evgeny Iakovlev, Petr Zhilyaev, Iskander AkhatovSubjects: Soft Condensed Matter (cond-mat.soft); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Recent experiments and computer simulations observe various geometrical formations of nanobubbles in van der Waals heterostructures. Among the well studied dome and tent geometries, there is yet least understood pancake graphene nanobubbles (GNB). This more exotic form exhibits discrete values of vertical sizes around just a few diameters of the molecules trapped inside the GNBs. We develop a model based on the membrane theory and confined fluids thermodynamics. Our approach describes the equilibrium properties of such flat GNBs. We show that discrete pancake geometry is the result of disjoining pressure induced by the trapped fluid inside GNB. The calculated total energy defines a discrete series of the metastable states with the pancake heights, which are multiple to molecular diameter. We observe that the value and the distribution of the total energy minima crucially depend on the temperature. The energy barriers between metastable states decrease as the temperature becomes larger. Also, we demonstrate that the pancake forms are favorable in the cases of sufficiently low membrane-substrate adhesion energy and the small number of trapped molecules. These properties are in agreement with the published simulations and experiments. The numerical comparison of our result with molecular dynamics results additionally shows the adequacy of the proposed model.
- arXiv:2003.05424 [pdf, other]
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Title: Dual Majorana universality in thermally induced nonequilibriumAuthors: Sergey SmirnovComments: 7 pages, 7 figuresJournal-ref: Physical Review B 101, 125417 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Superconductivity (cond-mat.supr-con)
We demonstrate that nonequilibrium nanoscopic systems with Majorana zero modes admit special kind of universality which cannot be classified as of strictly transport or strictly thermodynamic nature. To reveal such kind of Majorana universality we explore purely thermal nonequilibrium states of a quantum dot whose low-energy degrees of freedom are governed by Majorana zero modes. Specifically, the quantum dot is coupled to a topological superconductor, supporting Majorana zero modes, as well as to two normal metallic contacts with the same chemical potentials but different temperatures. It is shown that the Majorana universality in this setup is dual: it is stored inside both the response of the electric current, excited by exclusively the temperature difference, and the quantum dot compressibility. The latter is defined as the derivative of the quantum dot particle number with respect to the chemical potential and forms a universal Majorana ratio with a proper derivative of the electric current that flows in nonequilibrium states of purely thermal nature.
Replacements
- arXiv:1408.3663 (replaced) [pdf, ps, other]
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Title: Emergence of a non-Fowler-Nordheim-type behavior for a general planar tunneling barrierComments: 5 pages. Improved version. Title modified. Abstract rewritten. References updatedJournal-ref: Physics Letters A (2020)Subjects: Materials Science (cond-mat.mtrl-sci)
In this work we investigate a generalized tunneling barrier for planar emitters at zero-temperature. We present the evidence of the emergence of a non-Fowler-Nordheim-type general behavior for the field emission current density in the case that the Fermi energy ($\mu$) is comparable with or smaller that the decay width ($d_F$). Therefore, for some non-metals or materials that have very small Fermi energy the standard Fowler-Nordheim-type theory may require a correction. In the opposite regime, i.e., for $\mu$ much larger that $d_F$, we confirm that the conventional theory is suitable for metals.
- arXiv:1711.09963 (replaced) [pdf, ps, other]
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Title: Systolic aspects of black hole entropyAuthors: Nikolaos KalogeropoulosComments: 20 pages. No figures. LaTeX2e. This version: change of the author's affiliation. Other minor changes. To be published in a Special Issue of "Axioms" on "Theory and Mathematical Aspects of Black Holes"Journal-ref: Axioms 9(1), 30 (2020)Subjects: General Relativity and Quantum Cosmology (gr-qc); Statistical Mechanics (cond-mat.stat-mech); High Energy Physics - Theory (hep-th); Mathematical Physics (math-ph)
We attempt to provide a mesoscopic treatment of the origin of black hole entropy in (3+1)-dimensional spacetimes. We ascribe this entropy to the non-trivial topology of the space-like sections $\Sigma$ of the horizon. This is not forbidden by topological censorship, since all the known energy inequalities needed to prove the spherical topology of $\Sigma$ are violated in quantum theory. We choose the systoles of $\Sigma$ to encode its complexity, which gives rise to the black hole entropy. We present hand-waving reasons why the entropy of the black hole can be considered as a function of the volume entropy of $\Sigma$. We focus on the limiting case of $\Sigma$ having a large genus.
- arXiv:1808.07671 (replaced) [pdf, other]
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Title: Breakdown of the Fermi polaron description near Fermi degeneracy at unitarityComments: 18 pages, 7 figuresSubjects: Quantum Gases (cond-mat.quant-gas)
We theoretically investigate attractive Fermi polarons in three dimensions at finite temperature and impurity concentration through the many-body T-matrix theory and high-temperature virial expansion. By using the analytically continued impurity Green's function, we calculate the direct rf spectroscopy of attractive polarons in the unitary regime. Taking the peak value of the rf spectroscopy as the polaron energy and the full width half maximum as the polaron lifetime, we determine the temperature range of validity for the quasi-particle description of Fermi polarons in the unitary limit.
- arXiv:1810.13293 (replaced) [pdf, other]
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Title: Heavy-electron quantum criticality and single-particle spectroscopyAuthors: Stefan Kirchner, Silke Paschen, Qiuyun Chen, Steffen Wirth, Donglai Feng, Joe D. Thompson, Qimiao SiComments: 23 pages, 13 figures, 1 table; Colloquia section of Reviews of Modern PhysicsJournal-ref: Rev. Mod. Phys. vol. 92, 011002 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el); Materials Science (cond-mat.mtrl-sci)
Angle-resolved photoemission spectroscopy (ARPES) and scanning tunneling microscopy (STM) have become indispensable tools in the study of correlated quantum materials. Both probe complementary aspects of the single-particle excitation spectrum. Taken together, ARPES and STM have the potential to explore properties of the electronic Green's function, a central object of many-body theory. This review explicates this potential with a focus on heavy-electron quantum criticality, especially the role of Kondo destruction. A discussion on how to probe the Kondo destruction effect across the quantum-critical point using ARPES and STM measurements is presented. Particular emphasis is placed on the question of how to distinguish between the signatures of the initial onset of hybridization-gap formation, which is the "high-energy" physics to be expected in all heavy-electron systems, and those of Kondo destruction, which characterizes the low-energy physics and, hence, the nature of quantum criticality. Recent progress and possible challenges in the experimental investigations are surveyed, the STM and ARPES spectra for several quantum-critical heavy-electron compounds are compared, and the prospects for further advances are outlined.
- arXiv:1902.11172 (replaced) [pdf, other]
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Title: Magnetic structure and spin waves in the frustrated ferro-antiferromagnet Pb$_2$VO(PO$_4$)$_2$Authors: Simon Bettler, Florian Landolt, Ömer M. Aksoy, Zewu Yan, Severian Gvasaliya, Yiming Qiu, Eric Ressouche, Ketty Beauvois, Stéphane Raymond, Alexey N. Ponomaryov, Sergei A. Zvyagin, Andrey ZheludevJournal-ref: Phys. Rev. B 99, 184437 (2019)Subjects: Strongly Correlated Electrons (cond-mat.str-el)
Single crystal neutron diffraction, inelastic neutron scattering and electron spin resonance experiments are used to study the magnetic structure and spin waves in Pb$_2$VO(PO$_4$)$_2$, a prototypical layered $S=1/2$ ferromagnet with frustrating next nearest neighbor antiferromagnetic interactions. The observed excitation spectrum is found to be inconsistent with a simple square lattice model previously proposed for this material. At least four distinct exchange coupling constants are required to reproduce the measured spin wave dispersion. The degree of magnetic frustration is correspondingly revised and found to be substantially smaller than in all previous estimates.
- arXiv:1903.00552 (replaced) [pdf, other]
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Title: One-Component Order Parameter in URu$_2$Si$_2$ Uncovered by Resonant Ultrasound Spectroscopy and Machine LearningAuthors: Sayak Ghosh, Michael Matty, Ryan Baumbach, Eric D. Bauer, K. A. Modic, Arkady Shekhter, J. A. Mydosh, Eun-Ah Kim, B. J. RamshawJournal-ref: Sci. Adv. 6, eaaz4074 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el); Data Analysis, Statistics and Probability (physics.data-an)
The unusual correlated state that emerges in URu$_2$Si$_2$ below T$_{HO}$ = 17.5 K is known as "hidden order" because even basic characteristics of the order parameter, such as its dimensionality (whether it has one component or two), are "hidden". We use resonant ultrasound spectroscopy to measure the symmetry-resolved elastic anomalies across T$_{HO}$. We observe no anomalies in the shear elastic moduli, providing strong thermodynamic evidence for a one-component order parameter. We develop a machine learning framework that reaches this conclusion directly from the raw data, even in a crystal that is too small for traditional resonant ultrasound. Our result rules out a broad class of theories of hidden order based on two-component order parameters, and constrains the nature of the fluctuations from which unconventional superconductivity emerges at lower temperature. Our machine learning framework is a powerful new tool for classifying the ubiquitous competing orders in correlated electron systems.
- arXiv:1903.08060 (replaced) [pdf, other]
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Title: Hidden self-energies as origin of cuprate superconductivity revealed by machine learningComments: 27 pages, 17 figuresSubjects: Strongly Correlated Electrons (cond-mat.str-el)
Experimental data are the source of understanding matter. However, measurable quantities are limited and theoretically important quantities are often hidden. Nonetheless, recent progress of machine-learning techniques opens possibilities of exposing them only from available experimental data. In this article, the Boltzmann-machine method is applied to the angle-resolved photoemission spectroscopy spectra of cuprate superconductors. We find prominent peak structures both in normal and anomalous self-energies, but they cancel in the total self-energy making the structure apparently invisible, while the peaks make dominant contributions to superconducting gap, hence providing a decisive testimony for the origin of superconductivity. The relation between superfluid density and critical temperature supports involvement of universal carrier relaxation time associated with dissipative strange metals. The present achievement opens avenues for innovative machine-learning spectroscopy method.
- arXiv:1903.08348 (replaced) [pdf, other]
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Title: Global Stability Properties of the Climate: Melancholia States, Invariant Measures, and Phase TransitionsComments: 48 Pages, 10 FiguresSubjects: Atmospheric and Oceanic Physics (physics.ao-ph); Earth and Planetary Astrophysics (astro-ph.EP); Statistical Mechanics (cond-mat.stat-mech); Chaotic Dynamics (nlin.CD)
For a wide range of values of the incoming solar radiation, the Earth features at least two attracting states, which correspond to competing climates. The warm climate is analogous to the present one; the snowball climate features global glaciation and conditions that can hardly support life forms. Paleoclimatic evidences suggest that in the past our planet flipped between these two states. The main physical mechanism responsible for such an instability is the ice-albedo feedback. In a previous work, we defined the Melancholia states that sit between the two climates. Such states are embedded in the boundaries between the two basins of attraction and feature extensive glaciation down to relatively low latitudes. Here, we explore the global stability properties of the system by introducing random perturbations as modulations to the intensity of the incoming solar radiation. We observe noise-induced transitions between the competing basins of attraction. In the weak noise limit, large deviation laws define the invariant measure, the statistics of escape times, and typical escape paths called instantons. By constructing the instantons empirically, we show that the Melancholia states are the gateways for the noise-induced transitions. In the region of multistability, in the zero-noise limit, the measure is supported only on one of the competing attractors. For low (high) values of the solar irradiance, the limit measure is the snowball (warm) climate. The changeover between the two regimes corresponds to a first-order phase transition in the system. The framework we propose seems of general relevance for the study of complex multistable systems. Finally, we put forward a new method for constructing Melancholia states from direct numerical simulations, black which provides a possible alternative with respect to the edge-tracking algorithm.
- arXiv:1904.02157 (replaced) [pdf, other]
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Title: Observation of a thermoelectric Hall plateau in the extreme quantum limitAuthors: Wenjie Zhang, Peipei Wang, Brian Skinner, Ran Bi, Vladyslav Kozii, Chang-Woo Cho, Ruidan Zhong, John Schneeloch, Dapeng Yu, Genda Gu, Liang Fu, Xiaosong Wu, Liyuan ZhangComments: 17+21 pages, 3+14 figures; published versionJournal-ref: Nat. Commun. 11, 1046 (2020)Subjects: Materials Science (cond-mat.mtrl-sci); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
The thermoelectric Hall effect is the generation of a transverse heat current upon applying an electric field in the presence of a magnetic field. Here we demonstrate that the thermoelectric Hall conductivity $\alpha_{xy}$ in the three-dimensional Dirac semimetal ZrTe$_5$ acquires a robust plateau in the extreme quantum limit of magnetic field. The plateau value is independent of the field strength, disorder strength, carrier concentration, or carrier sign. We explain this plateau theoretically and show that it is a unique signature of three-dimensional Dirac or Weyl electrons in the extreme quantum limit. We further find that other thermoelectric coefficients, such as the thermopower and Nernst coefficient, are greatly enhanced over their zero-field values even at relatively low fields.
- arXiv:1904.06243 (replaced) [pdf, other]
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Title: The magnetic structure factor of correlated moments in small-angle neutron scatteringJournal-ref: Phys. Rev. B 101, 134401 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
The interplay between structural and magnetic properties of nanostructured magnetic materials allows to realize unconventional magnetic effects, which results in a demand for experimental techniques to determine the magnetization profile with nanoscale resolution. Magnetic small-angle neutron scattering (SANS) probes both the chemical and magnetic nanostructure and is thus a powerful technique e.g. for the characterization of magnetic nanoparticles. Here, we show that the conventionally used particle-matrix approach to describe SANS of magnetic particle assemblies, however, leads to a flawed interpretation. As remedy, we provide general expressions for the field-dependent 2D magnetic SANS cross-section of correlated moments. It is shown that for structurally disordered ensembles the magnetic structure factor is in general, and contrary to common assumptions, (i) anisotropic also in zero field, and (ii) that even in saturation the magnetic structure factor deviates from the nuclear one. These theoretical predictions explain qualitatively the intriguing experimental, polarized SANS data of an ensemble of dipolar-coupled iron oxide nanoparticles.
- arXiv:1905.07833 (replaced) [pdf, other]
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Title: Shaping the learning landscape in neural networks around wide flat minimaComments: 37 pages (16 main text), 10 figures (7 main text)Journal-ref: Proceedings of the National Academy of Sciences, 2020 Jan 7, 117 (1) 161-170Subjects: Machine Learning (cs.LG); Disordered Systems and Neural Networks (cond-mat.dis-nn); Machine Learning (stat.ML)
Learning in Deep Neural Networks (DNN) takes place by minimizing a non-convex high-dimensional loss function, typically by a stochastic gradient descent (SGD) strategy. The learning process is observed to be able to find good minimizers without getting stuck in local critical points, and that such minimizers are often satisfactory at avoiding overfitting. How these two features can be kept under control in nonlinear devices composed of millions of tunable connections is a profound and far reaching open question. In this paper we study basic non-convex one- and two-layer neural network models which learn random patterns, and derive a number of basic geometrical and algorithmic features which suggest some answers. We first show that the error loss function presents few extremely wide flat minima (WFM) which coexist with narrower minima and critical points. We then show that the minimizers of the cross-entropy loss function overlap with the WFM of the error loss. We also show examples of learning devices for which WFM do not exist. From the algorithmic perspective we derive entropy driven greedy and message passing algorithms which focus their search on wide flat regions of minimizers. In the case of SGD and cross-entropy loss, we show that a slow reduction of the norm of the weights along the learning process also leads to WFM. We corroborate the results by a numerical study of the correlations between the volumes of the minimizers, their Hessian and their generalization performance on real data.
- arXiv:1905.12523 (replaced) [pdf, other]
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Title: Coherent long-range transfer of angular momentum between magnon Kittel modes by phononsAuthors: Kyongmo An, Artem N. Litvinenko, Ryuhei Kohno, Aufa A. Fuad, Vladimir V. Naletov, Laurent Vila, Ursula Ebels, Grégoire de Loubens, Hervé Hurdequint, Nathan Beaulieu, Jamal Ben Youssef, Nicolas Vukadinovic, Gerrit E.W. Bauer, Andrei N. Slavin, Vasil S. Tiberkevich, Olivier KleinJournal-ref: Phys. Rev. B 101, 060407 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci)
We report ferromagnetic resonance in the normal configuration of an electrically insulating magnetic bilayer consisting of two yttrium iron garnet (YIG) films epitaxially grown on both sides of a 0.5-mm-thick nonmagnetic gadolinium gallium garnet (GGG) slab. An interference pattern is observed and it is explained as the strong coupling of the magnetization dynamics of the two YIG layers either in phase or out of phase by the standing transverse sound waves, which are excited through a magnetoelastic interaction. This coherent mediation of angular momentum by circularly polarized phonons through a nonmagnetic material over macroscopic distances can be useful for future information technologies.
- arXiv:1906.10296 (replaced) [pdf, other]
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Title: AC Oscillation of a Spin Soliton Driven by a Constant ForceComments: 9 pages, 6 figuresJournal-ref: Phys. Rev. A 101, 043621 (2020)Subjects: Quantum Gases (cond-mat.quant-gas)
The phenomena of AC oscillation generated by a DC drive, such as the famous Josephson AC effect in superconductors and Bloch oscillation in solid physics, are of great interest in physics. Here we report another example of such counter-intuitive phenomenon that a spin soliton in a two-component Bose-Einstein condensate is driven by a constant force: The initially static spin soliton first moves in a direction opposite to the force and then changes direction, showing an extraordinary AC oscillation in a long term. In sharp contrast to the Josephson AC effect and Bloch oscillation, we find that the nonlinear interactions play important roles and the spin soliton can exhibit a periodic transition between negative and positive inertial mass even in the absence of periodic potentials. We then develop an explicit quasiparticle model that can account for this extraordinary oscillation satisfactorily. Important implications and possible applications of our finding are discussed.
- arXiv:1907.07299 (replaced) [pdf, other]
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Title: Majorana-Magnon Crossover by a Magnetic Field in the Kitaev Model: Continuous-Time Quantum Monte Carlo StudyComments: 6 pages, 4 figures, accepter for the publication in Physical Review B: Rapid CommunicationsJournal-ref: Phys. Rev. B 101, 100408 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el)
Kitaev quantum spin liquids host Majorana fermions via the fractionalization of spins. In a magnetic field, the Majorana fermions were predicted to comprise a topological state, which has attracted great attention by the discovery of the half-quantized thermal Hall conductivity. Nevertheless, a reliable theory remains elusive for the field effect, especially at finite temperature. Here we present unbiased large-scale numerical results for the Kitaev model in a wide range of magnetic field and temperature. We find that the unconventional paramagnetic region showing fractional spin dynamics extends at finite temperature, far beyond the field range where the topological state is expected at zero temperature. Our results show the confinement-deconfinement behavior between the fractional Majorana excitations and the conventional magnons.
- arXiv:1909.10640 (replaced) [pdf, other]
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Title: Influences of microcontact shape on the state of a frictional interfaceComments: 5 pages, 4 figuresJournal-ref: Phys. Rev. Research 2, 012056 (2020)Subjects: Soft Condensed Matter (cond-mat.soft); Geophysics (physics.geo-ph)
The real area of contact of a frictional interface changes rapidly when the normal load is altered, and evolves slowly when normal load is held constant, aging over time. Traditionally, the total area of contact is considered a proxy for the frictional strength of the interface. Here we show that the state of a frictional interface is not entirely defined by the total real area of contact but depends on the geometrical nature of that contact as well. We directly visualize an interface between rough elastomers and smooth glass and identify that normal loading and frictional aging evolve the interface differently, even at a single contact level. We introduce a protocol wherein the real area of contact is held constant in time. Under these conditions, the interface is continually evolving; small contacts shrink and large contacts coarsen.
- arXiv:1910.09883 (replaced) [pdf, other]
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Title: Ergodicity and large deviations in physical systems with stochastic dynamicsAuthors: Robert L. JackComments: accepted version, small additions and modifications. 23 pages, "colloquium" articleSubjects: Statistical Mechanics (cond-mat.stat-mech)
In ergodic physical systems, time-averaged quantities converge (for large times) to their ensemble-averaged values. Large deviation theory describes rare events where these time averages differ significantly from the corresponding ensemble averages. It allows estimation of the probabilities of these events, and their mechanisms. This theory has been applied to a range of physical systems, where it has yielded new insights into entropy production, current fluctuations, metastability, transport processes, and glassy behaviour. We review some of these developments, identifying general principles. We discuss a selection of dynamical phase transitions, and we highlight some connections between large-deviation theory and optimal control theory.
- arXiv:1910.13748 (replaced) [pdf, ps, other]
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Title: Revisit the non-locality of Majorana zero modes and teleportation: Bogoliubov-de Gennes equation based treatmentComments: 12 pages, 4 figuresJournal-ref: Phys. Rev. B 101, 205401 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Quantum Physics (quant-ph)
The nonlocal nature of the Majorana zero modes implies an inherent teleportation channel and unique transport signatures for Majorana identification. In this work we make an effort to eliminate some inconsistencies between the Bogoliubov-de Gennes equation based treatment and the method using the associated regular fermion number states of vacancy and occupation within the `second quantization' framework. We first consider a rather simple `quantum dot--Majorana wire--quantum dot' system, then a more experimentally relevant setup by replacing the quantum dots with transport leads. For the latter setup, based on the dynamical evolution of electron-hole excitations, we develop a single-particle-wavefunction approach to quantum transport, which renders both the conventional quantum scattering theory and the steady-state nonequilibrium Green's function formalism as its stationary limit. Further, we revisit the issue of Majorana tunneling spectroscopy and consider in particular the two-lead coupling setup. We present comprehensive discussions with detailed comparisons, and predict a zero-bias-limit conductance of $e^2/h$ (for symmetric coupling to the leads),which is a half of the popular result of the zero-bias-peak, or, the so-called Majorana quantized conductance ($2e^2/h$). The present work may arouse a need to reexamine some existing studies and the proposed treatment is expected to be involved in analyzing future experiments in this fast developing field.
- arXiv:1911.03323 (replaced) [pdf]
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Title: Room temperature high charge to spin conversion in amorphous topological insulatorAuthors: Protyush Sahu, Jun-Yang Chen, Xavier Devaux, Henri Jaffres, Sylvie Migot, Huong Dang, Jean-Marie George, Javier Garcia-Barriocanal, Yuan Lu, Jian-Ping WangSubjects: Materials Science (cond-mat.mtrl-sci)
Disordered topological insulator (TI) films have gained intense interest because of their possibility for spintronic applications by befitting from TI's exotic transport properties. Here, we have fabricated disordered Gd-alloyed BixSe1-x (BSG) TI films by sputtering methods and have investigated their magneto-transport and spin-torque properties. Structural characterizations show a mainly amorphous feature for the 8 nm thick BSG film, while Bi rich crystallites are developed inside the 16 nm thick BSG film. The bulk resistivity of BSG film is found to be relatively high, up to 6 x 10^4 uOhm.cm, with respect to the resistivity of the polycrystalline BixSe1-x film. Temperature dependent resistivity measurements display the evident character of a variable range hopping transport from 80K to 300K. Second harmonic transport characterizations have been performed on the BSG (t)/ CFB (5 nm) bilayer structures with different thicknesses (t = 6, 8, 12, 16 nm). The effective spin Hall angle deduced form the damping-like torque shows a maximum value of 3.74 corresponding to 8 nm thick BSG at room temperature, which is one order of magnitude higher than that of heavy metals. The possible various origins of suck enhancement are discussed. Our study provides a new experimental direction, beyond crystalline solids, to search for topological systems in amorphous solids and other engineered random systems.
- arXiv:1911.05270 (replaced) [pdf, other]
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Title: Variety of order-by-disorder phases in the asymmetric $J_1-J_2$ zigzag ladder: From the delta chain to the $J_1-J_2$ chainComments: 18 pages, 17 figuresJournal-ref: Phys. Rev. B 101, 104407 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el)
We study an asymmetric $J_1$-$J_2$ zigzag ladder consisting of two different spin-$\frac{1}{2}$ antiferromagnetic (AFM; $J_2$, $\gamma J_2>0$) Heisenberg legs coupled by zigzag-shaped ferromagnetic (FM; $J_1<0$) inter-leg interaction. On the basis of density-matrix renormalization group based calculations the ground-state phase diagram is obtained as functions of $\gamma$ and $J_2/|J_1|$. It contains four kinds of frustration-induced ordered phases except a trivial FM phase. Two of the ordered phases are valence bond solid (VBS) with spin-singlet dimerization, which is a rather conventional order by disorder. Still, it is interesting to note that the VBS states possess an Affleck-Kennedy-Lieb-Tasaki-type topological hidden order. The remaining two phases are ferrimagnetic orders, each of which is distinguished by commensurate or incommensurate spin-spin correlation. It is striking that the ferrimagnetic orders are not associated with geometrical symmetry breaking; instead, the global spin-rotation symmetry is broken. In other words, the system lowers its energy via the FM inter-leg interaction by polarizing both of the AFM Heisenberg legs. This is a rare type of order by disorder. Besides, the incommensurate ferrimagnetic state appears as a consequence of the competition between a polarization and a critical Tomonaga-Luttinger-liquid behavior in the AFM Heisenberg legs.
- arXiv:1911.08246 (replaced) [pdf, other]
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Title: Resolving the positions of defects in superconducting quantum bitsAuthors: Alexander Bilmes, Anthony Megrant, Paul Klimov, Georg Weiss, John M. Martinis, Alexey V. Ustinov, Jürgen LisenfeldSubjects: Quantum Physics (quant-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Instrumentation and Detectors (physics.ins-det)
Solid-state quantum coherent devices are quickly progressing. Superconducting circuits, for instance, have already been used to demonstrate prototype quantum processors comprising a few tens of quantum bits. This development also revealed that a major part of decoherence and energy loss in such devices originates from a bath of parasitic material defects. However, neither the microscopic structure of defects nor the mechanisms by which they emerge during sample fabrication are understood. Here, we present a technique to obtain information on locations of defects relative to the thin film edge of the qubit circuit. Resonance frequencies of defects are tuned by exposing the qubit sample to electric fields generated by electrodes surrounding the chip. By determining the defect's coupling strength to each electrode and comparing it to a simulation of the field distribution, we obtain the probability at which location and at which interface the defect resides. This method is applicable to already existing samples of various qubit types, without further on-chip design changes. It provides a valuable tool for improving the material quality and nano-fabrication procedures towards more coherent quantum circuits.
- arXiv:1911.11072 (replaced) [pdf, ps, other]
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Title: Large non-reciprocal propagation of surface acoustic waves in epitaxial ferromagnetic/semiconductor hybrid structuresJournal-ref: Phys. Rev. Applied 13, 044018 (2020)Subjects: Applied Physics (physics.app-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci)
Non-reciprocal propagation of sound, that is, the different transmission of acoustic waves traveling along opposite directions, is a challenging requirement for the realization of devices like acoustic isolators and circulators. Here, we demonstrate the efficient non-reciprocal transmission of surface acoustic waves (SAWs) propagating along opposite directions of a GaAs substrate coated with an epitaxial Fe$_3$Si film. The non-reciprocity arises from the acoustic attenuation induced by the magneto-elastic (ME) interaction between the SAW strain field and spin waves in the ferromagnetic film, which depends on the SAW propagation direction and can be controlled via the amplitude and orientation of an external magnetic field. The acoustic transmission non-reciprocity, defined as the difference between the transmitted acoustic power for forward and backward propagation under ME resonance, reaches values of up to 20%, which are, to our knowledge, the largest non-reciprocity reported for SAWs traveling along a semiconducting piezoelectric substrate covered by a ferromagnetic film. The experimental results are well accounted for by a model for ME interaction, which also shows that non-reciprocity can be further enhanced by optimization of the sample design. These results make Fe$_3$Si/GaAs a promising platform for the realization of efficient non-reciprocal SAW devices.
- arXiv:1911.11602 (replaced) [pdf, ps, other]
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Title: Dissipation induced Luttinger liquid correlations in a one dimensional Fermi gasComments: 5 pages, 2 figures + supplementary materialJournal-ref: Phys. Rev. Lett. 124, 136401 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el); Quantum Gases (cond-mat.quant-gas)
We study a one-dimensional Fermi gas in the presence of dissipative coupling to environment through the Lindblad equation. The dissipation involves energy exchange with the environment and favours the relaxation of electrons to excitations. After switching on the dissipation, the system approaches a steady state, which is described by a generalized Gibbs ensemble. The fermionic single particle density matrix resembles deceivingly to that in a hermitian interaction quench. It decays inversely with the distance for short times due to the fermionic correlations in the initial state, which changes into a non-integer power law decay for late times, representing dissipation induced Luttinger liquid behaviour. However, the crossover between the two regions occurs due to dissipation induced damping, and is unrelated to the propagation of excitations. The velocity of information spreading is set by the dissipative coupling, and differs significantly from the original sound velocity. The thermodynamic entropy grows as $-t\ln t$ initially, and saturates to an extensive value. Our results can be tested experimentally in one-dimensional Dirac systems.
- arXiv:1911.12741 (replaced) [pdf, other]
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Title: Finite-size effects in the nonphononic density of states in computer glassesAuthors: Edan LernerComments: 5 pages, 3 figures. v2: data for larger systems included in fig.3Journal-ref: Phys. Rev. E 101, 032120 (2020)Subjects: Soft Condensed Matter (cond-mat.soft)
The universal form of the density of nonphononic, quasilocalized vibrational modes of frequency $\omega$ in structural glasses, ${\cal D}(\omega)$, was predicted theoretically decades ago, but only recently revealed in numerical simulations. In particular, it has been recently established that, in generic computer glasses, ${\cal D}(\omega)$ increases from zero frequency as $\omega^4$, independent of spatial dimension and of microscopic details. However, in [E. Lerner, and E. Bouchbinder, Phys. Rev. E 96, 020104(R) (2017)] it was shown that the preparation protocol employed to create glassy samples may affect the form of their resulting ${\cal D}(\omega)$: glassy samples rapidly quenched from high temperature liquid states were shown to feature ${\cal D}(\omega)\!\sim\!\omega^\beta$ with $\beta\!<\!4$, presumably limiting the degree of universality of the $\omega^4$ law. Here we show that exponents $\beta\!<\!4$ are only seen in small glassy samples quenched from high-temperatue liquid states --- whose sizes are comparable to or smaller than the size of the disordered core of soft quasilocalized vibrations --- while larger glassy samples made with the same protocol feature the universal $\omega^4$ law. Our results demonstrate that observations of $\beta\!<\!4$ in the nonphononic density of states stem from finite-size effects, and we thus conclude that the $\omega^4$ law should be featured by any sufficiently large glass quenched from a melt.
- arXiv:1912.02688 (replaced) [pdf, other]
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Title: Competition between local erasure and long-range spreading of a single biochemical mark leads to epigenetic bistabilityComments: 11 pages, 7 figures, 2 appendicesJournal-ref: Phys. Rev. E 101, 042408 (2020)Subjects: Biological Physics (physics.bio-ph); Soft Condensed Matter (cond-mat.soft)
The mechanism through which cells determine their fate is intimately related to the spreading of certain biochemical (so-called epigenetic) marks along their genome. The mechanisms behind mark spreading and maintenance are not yet fully understood, and current models often assume a long-range infection-like process for the dynamics of marks, due to the polymeric nature of the chromatin fibre which allows looping between distant sites. While these existing models typically consider antagonising marks, here we propose a qualitatively different scenario which analyses the spreading of a single mark. We define a 1D stochastic model in which mark spreading/infection occurs as a long-range process whereas mark erasure/recovery is a local process, with an enhanced rate at boundaries of infected domains. In the limiting case where our model exhibits absorbing states, we find a first-order-like transition separating the marked/infected phase from the unmarked/recovered phase. This suggests that our model, in this limit, belongs to the long-range compact directed percolation universality class. The abrupt nature of the transition is retained in a more biophysically realistic situation when a basal infection/recovery rate is introduced (thereby removing absorbing states). Close to the transition there is a range of bistability where both the marked/infected and unmarked/recovered states are metastable and long lived, which provides a possible avenue for controlling fate decisions in cells. Increasing the basal infection/recovery rate, we find a second transition between a coherent (marked or unmarked) phase, and a mixed, or random, one.
- arXiv:1912.03529 (replaced) [pdf, ps, other]
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Title: Tensor network renormalization group study of spin-1 random Heisenberg chainsComments: 10 pages, 12 figuresJournal-ref: Eur. Phys. J. B 93, 63 (2020)Subjects: Disordered Systems and Neural Networks (cond-mat.dis-nn); Strongly Correlated Electrons (cond-mat.str-el)
We use a tensor network strong-disorder renormalization group (tSDRG) method to study spin-1 random Heisenberg antiferromagnetic chains. The ground state of the clean spin-1 Heisenberg chain with uniform nearest-neighbor couplings is a gapped phase known as the Haldane phase. Here we consider disordered chains with random couplings, in which the Haldane gap closes in the strong disorder regime. As the randomness strength is increased further and exceeds a certain threshold, the random chain undergoes a phase transition to a critical random-singlet phase. The strong-disorder renormalization group method formulated in terms of a tree tensor network provides an efficient tool for exploring ground-state properties of disordered quantum many-body systems. Using this method we detect the quantum critical point between the gapless Haldane phase and the random-singlet phase via the disorder-averaged string order parameter. We determine the critical exponents related to the average string order parameter, the average end-to-end correlation function and the average bulk spin-spin correlation function, both at the critical point and in the random-singlet phase. Furthermore, we study energy-length scaling properties through the distribution of energy gaps for a finite chain. Our results are in closer agreement with the theoretical predictions than what was found in previous numerical studies. As a benchmark, a comparison between tSDRG results for the average spin correlations of the spin-1/2 random Heisenberg chain with those obtained by using unbiased zero-temperature QMC method is also provided.
- arXiv:1912.04124 (replaced) [pdf, other]
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Title: Polarizabilities of complex individual dielectric or plasmonic nanostructuresAuthors: Adelin Patoux, Clément Majorel, Peter R. Wiecha, Aurélien Cuche, Otto L. Muskens, Christian Girard, Arnaud ArbouetComments: 13 pages, 11 figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
When the sizes of photonic nanoparticles are much smaller than the excitation wavelength, their optical response can be efficiently described with a series of polarizability tensors. Here, we propose a universal method to extract the different components of the response tensors associated with small plasmonic or dielectric particles. We demonstrate that the optical response can be faithfully approximated, as long as the effective dipole is not induced by retardation effects, hence do not depend on the phase of the illumination. We show that the conventional approximation breaks down for a phase-driven dipolar response, such as optical magnetic resonances in dielectric nanostructures. To describe such retardation induced dipole resonances in intermediate-size dielectric nanostructures, we introduce "pseudo-polarizabilities" including first-order phase effects, which we demonstrate at the example of magnetic dipole resonances in dielectric spheres and ellipsoids. Our method paves the way for fast simulations of large and inhomogeneous meta-surfaces.
- arXiv:1912.04547 (replaced) [pdf, ps, other]
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Title: Volume dependent extension of Kerr-Newman black hole thermodynamicsComments: 6 pages, 1 figure; accepted for publication in Phys. Lett. BJournal-ref: Phys. Lett. B 803 (2020) 135344Subjects: General Relativity and Quantum Cosmology (gr-qc); Statistical Mechanics (cond-mat.stat-mech); High Energy Physics - Theory (hep-th)
We show that the Hawking--Bekenstein entropy formula is modified by a factor of $8/3$ if one also considers a work term in the 1st law of thermodynamics by a pressure stemming from the Hawking radiation. We give an intuitive definition for the corresponding thermodynamical volume by the implicit definition $\epsilon=Mc^2/V$, which is the average energy density of the Hawking radiation. This volume scales as $V \sim M^5$, agreeing with other suggestions. As a result the corresponding Smarr relation describes an extensive entropy and a stable effective equation of state $S(E,V)\sim E^{3/4}V^{1/4}$. These results pertain for charged and rotating Kerr-Newman black holes.
- arXiv:1912.06784 (replaced) [pdf, other]
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Title: Magnetic Flux Periodicity in Second Order Topological SuperconductorsComments: 9 pages, 11 figuresJournal-ref: Phys. Rev. B 101, 125429 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Superconductivity (cond-mat.supr-con)
The magnetic flux periodicity of $\frac{hc}{2e}$ is a well known manifestation of Cooper pairing in typical s-wave superconductors. In this paper we theoretically show that the flux periodicity of a two-dimensional second-order topological superconductor, which features zero-energy Majorana modes localized at the corners of the sample, is $\frac{hc}{e}$ instead. We further show that the periodicity changes back to $\frac{hc}{2e}$ at the transition to a topologically trivial superconductor, where the Majorana modes hybridize with the bulk states, demonstrating that the doubling of periodicity is a manifestation of the non-trivial topology of the state.
- arXiv:1912.10907 (replaced) [pdf, ps, other]
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Title: Multivariate Group Entropies, Super-exponentially Growing Systems and Functional EquationsAuthors: Piergiulio TempestaComments: 15 pagesSubjects: Mathematical Physics (math-ph); Statistical Mechanics (cond-mat.stat-mech)
We define the class of multivariate group entropies, first investigated in [22], as a natural generalization of the $Z$-entropies introduced in [32]. We propose new examples related to the "super-exponential" universality class of complex systems; in particular, we introduce a general entropy, suitable for this class. We also show that the group-theoretical structure associated with our multivariate entropies can be used to define a large family of exactly solvable discrete dynamical models. The natural mathematical framework allowing us to formulate this correspondence is offered by the theory of formal groups and rings.
- arXiv:1912.13425 (replaced) [pdf, other]
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Title: Inflationary routes to Gaussian curved topographyComments: 17 pages, 12 figuresSubjects: Soft Condensed Matter (cond-mat.soft)
Gaussian-curved shapes are obtained by inflating initially flat systems made of two superimposed strong and light thermoplastic impregnated fabric sheets heat-sealed together along a specific network of lines. The resulting inflated structures are light and very strong because they (largely) resist deformation by the intercession of stretch. Programmed patterns of channels vary either discretely through boundaries, or continuously. The former give rise to facetted structures that are in effect non-isometric origami and which cannot unfold as in conventional folded structures, since they present localized angle deficit or surplus. Continuous variation of channel direction in the form of spirals is examined, giving rise to curved shells. We solve the inverse problem consisting in finding a network of seam lines leading to a target axisymmetric shape on inflation. They too have strength from the metric changes that have been pneumatically driven, resistance to change being met with stretch and hence high forces like typical shells .
- arXiv:2001.01094 (replaced) [pdf, ps, other]
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Title: Unified analytic expressions for the entanglement length, tube diameter, and plateau modulus of polymer meltsComments: Accepted for publication in Physical Review LettersJournal-ref: Phys. Rev. Lett. 124, 147801 (2020)Subjects: Soft Condensed Matter (cond-mat.soft)
By combining molecular dynamics simulations and topological analyses with scaling arguments, we obtain analytic expressions that quantitatively predict the entanglement length $N_e$, the plateau modulus $G$, and the tube diameter $a$ in melts that span the entire range of chain stiffnesses for which systems remain isotropic. Our expressions resolve conflicts between previous scaling predictions for the loosely entangled [Lin-Noolandi: $G\ell_K^3/k_\textrm{B}T \sim (\ell_K/p)^3$], semiflexible [Edwards/de Gennes: $G\ell_K^3/k_\textrm{B}T \sim (\ell_K/p)^2$], and tightly-entangled [Morse: $G\ell_K^3/k_\textrm{B}T \sim (\ell_K/p)^{1+\epsilon}$] regimes, where $\ell_K$ and $p$ are respectively the Kuhn and packing lengths. We also find that maximal entanglement (minimal $N_e$) coincides with the onset of local nematic order.
- arXiv:2001.04746 (replaced) [pdf, other]
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Title: Collective magnetic dynamics in artificial spin ice probed by AC susceptibilityAuthors: Merlin Pohlit, Giuseppe Muscas, Ioan-Augustin Chioar, Henry Stopfel, Agne Ciuciulkaite, Erik Östman, Spyridon D. Pappas, Aaron Stein, Björgvin Hjörvarsson, Petra E. Jönsson, Vassilios KapaklisComments: 7 pages, 4 figuresJournal-ref: Phys. Rev. B 101, 134404 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We report on the study of the thermal dynamics of square artificial spin ice, probed by means of temperature and frequency dependent AC susceptibility. Pronounced influence of the inter-island coupling strength was found on the frequency response of the samples. Through the subsequent analysis of the frequency- and coupling-dependent freezing temperatures, we discuss the phenomenological parameters obtained in the framework of Vogel-Fulcher-Tammann law in terms of the samples microscopic features. The high sensitivity and robust signal to noise ratio of AC susceptibility validates the latter as a promising and simple experimental technique for resolving the dynamics and temperature driven dynamics crossovers for the case of artificial spin ice.
- arXiv:2001.05135 (replaced) [pdf, other]
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Title: Nonreciprocal surface acoustic wave propagation via magneto-rotation couplingAuthors: Mingran Xu, Kei Yamamoto, Jorge Puebla, Korbinian Baumgaertl, Bivas Rana, Katsuya Miura, Hiromasa Takahashi, Dirk Grundler, Sadamichi Maekawa, Yoshichika OtaniComments: 23 pages, 10 figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Applied Physics (physics.app-ph)
One of the most fundamental forms of magnon-phonon interaction is an intrinsic property of magnetic materials, the magnetoelastic coupling. This particular form of interaction has been the basis for describing magnetic materials and their strain related applications, where strain induces changes of internal magnetic fields. Different from the magnetoelastic coupling, more than 40 years ago, it was proposed that surface acoustic waves may induce surface magnons via rotational motion of the lattice in anisotropic magnets. However, a signature of this magnon-phonon coupling mechanism, termed magneto-rotation coupling, has been elusive. Here, we report the first observation and theoretical framework of the magneto-rotation coupling in a perpendicularly anisotropic ultra-thin film Ta/CoFeB(1.6 nm)/MgO, which consequently induces nonreciprocal acoustic wave attenuation with an unprecedented ratio up to 77$\%$ and theoretically predicted 100$\%$ rectification at the optimized condition. Our work not only experimentally demonstrates a fundamentally new path for investigating magnon-phonon coupling, but also justify the feasibility of the magneto-rotation coupling based application.
- arXiv:2001.07971 (replaced) [pdf, other]
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Title: Time-Dependent Ginzburg-Landau Simulations of Superconducting Vortices in Three DimensionsJournal-ref: Low Temperature Physics/Fizika Nizkikh Temperatur, 2020, v. 46, N. 4, pp. 386-394Subjects: Superconductivity (cond-mat.supr-con)
Here we describe a development of computer algorithm to simulate the Time Dependent Ginzburg-Landau equation (TDGL) and its application to understand superconducting vortex dynamics in confined geometries. Our initial motivation to get involved in this task was trying to understand better our experimental measurements on dynamics of superconductors with vortices at high frequencies leading to microwave stimulated superconductivity due to presence of vortex (Lara, et al., Scientific Reports, 59187 (2015)).
- arXiv:2002.03000 (replaced) [pdf, other]
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Title: Parallel PERMSubjects: Statistical Mechanics (cond-mat.stat-mech); Soft Condensed Matter (cond-mat.soft)
We develop and implement a parallel flatPERM algorithm \cite{G97,PK04} with mutually interacting parallel flatPERM sequences and use it to sample self-avoiding walks in 2 and 3 dimensions. Our data show that the parallel implementation accelerates the convergence of the flatPERM algorithm. Moreover, increasing the number of interacting flatPERM sequences (rather than running longer simulations) improves the rate of convergence. This suggests that a more efficient implementation of flatPERM will be a massively parallel implementation, rather than long simulations of one, or a few parallel sequences. We also use the algorithm to estimate the growth constant of the self-avoiding walk in two and in three dimensions using simulations over 12 parallel sequences. Our best results are \[ \mu_d = \cases{ 2.6381585(1), & \hbox{if $d=2$}; \cr 4.684039(1), & \hbox{if $d=3$}. } \]
- arXiv:2002.11556 (replaced) [pdf, other]
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Title: Nonequilibrium Phase Transitions in Repulsive Binary MixturesSubjects: Statistical Mechanics (cond-mat.stat-mech); Soft Condensed Matter (cond-mat.soft)
We consider rapid cooling processes in classical, 3-dimensional, purely repulsive binary mixtures in which an initial infinite-temperature configuration is instantly quenched to zero temperature. It is found that such systems display both kinds of possible continuous nonequilibrium transition, characterized by either a conserved or non-conserved order parameter. The type of transition that is observed can be controlled by tuning the interactions between unlike particles, with strong inter-species repulsion leading to chemical ordering in terms of an unmixing process, whereas weak repulsion gives rise to spontaneous crystallization, maintaining chemical homogeneity. In contrast to common first-order equilibrium freezing transitions, this nonequilibrium crystallization phenomenon is continuous in nature, being barrierless and producing grain-size distributions that display scale-invariant features. Furthermore, the results suggest that the dual-type transition behavior is universal for repulsive pair interaction potential-energy functions in general, with the propensity for the continuous freezing transition being related to their behavior in the neighborhood of zero separation.
- arXiv:2003.00915 (replaced) [pdf, ps, other]
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Title: On dimension of tetrads in effective gravityAuthors: G.E. VolovikComments: 3 pages, no figures, version accepted in JETP LettersSubjects: General Relativity and Quantum Cosmology (gr-qc); Other Condensed Matter (cond-mat.other); High Energy Physics - Phenomenology (hep-ph)
Two different sources of emergent gravity lead to the inverse square of length dimension of metric field, $[g_{\mu\nu}]=1/[l]^2$, as distinct from the conventional dimensionless metric, $[g_{\mu\nu}]=1$, for $c = 1$. In both scenarios all the physical quantities, which obey diffeomorphism invariance, such as the Newton constant, the scalar curvature, the cosmological constant, particle masses, fermionic and scalar bosonic fields, etc., are dimensionless.
- arXiv:2003.03430 (replaced) [pdf, other]
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Title: Photon-mediated charge-exchange reactions between 39K atoms and 40Ca+ ions in a hybrid trapAuthors: Hui Li, S. Jyothi, Ming Li, Jacek Klos, Alexander Petrov, Kenneth R Brown, Svetlana KotochigovaComments: 13 pages, 16 figuresJournal-ref: Phys. Chem. Chem. Phys., 2020,22, 10870-10881Subjects: Atomic Physics (physics.atom-ph); Quantum Gases (cond-mat.quant-gas)
We present experimental evidence of charge exchange between laser-cooled potassium $^{39}$K atoms and calcium $^{40}$Ca$^+$ ions in a hybrid atom-ion trap and give quantitative theoretical explanations for the observations. The $^{39}$K atoms and $^{40}$Ca$^+$ ions are held in a magneto-optical (MOT) and a linear Paul trap, respectively. Fluorescence detection and high resolution time of flight mass spectra for both species are used to determine the remaining number of $^{40}$Ca$^+$ ions, the increasing number of $^{39}$K$^+$ ions, and $^{39}$K number density as functions of time. Simultaneous trap operation is guaranteed by alternating periods of MOT and $^{40}$Ca$^+$ cooling lights, thus avoiding direct ionization of $^{39}$K by the $^{40}$Ca$^+$ cooling light. We show that the K-Ca$^+$ charge-exchange rate coefficient increases linearly from zero with $^{39}$K number density and, surprisingly, the fraction of $^{40}$Ca$^+$ ions in the 4p\,$^2$P$_{1/2}$ electronically-excited state. Combined with our theoretical analysis, we conclude that these data can only be explained by a process that starts with a potassium atom in its electronic ground state and a calcium ion in its excited 4p\,$^2$P$_{1/2}$ state producing ground-state $^{39}$K$^+$ ions and metastable, neutral Ca\,(3d4p$^3$P$_1$) atoms, releasing only 150 cm$^{-1}$ equivalent relative kinetic energy. Charge-exchange between either ground- or excited-state $^{39}$K and ground-state $^{40}$Ca$^+$ is negligibly small as no energetically-favorable product states are available. Our experimental and theoretical rate coefficients of $9\times10^{-10}$ cm$^3$/s are in agreement given the uncertainty budgets.
- arXiv:2003.03448 (replaced) [pdf]
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Title: Strengthening the magnetic interactions in pseudobinary first-row transition metal thiocyanates, $\it{M}$(NCS)$_{2}$Authors: Euan N. Bassey, Joseph A. M. Paddison, Evan N. Keyzer, Jeongjae Lee, Pascal Manuel, Ivan da Silva, Siân E. Dutton, Clare P. Grey, Matthew J. CliffeComments: 17 pages, 10 figuresSubjects: Materials Science (cond-mat.mtrl-sci); Strongly Correlated Electrons (cond-mat.str-el)
Understanding the effect of chemical composition on the strength of magnetic interactions is key to the design of magnets with stronger exchange interactions. The magnetic divalent first-row transition metal (TM) thiocyanates are a class of chemically simple layered molecular frameworks. Here, we report two new members of the family, manganese (II) thiocyanate, Mn(NCS)$_{2}$, and iron (II) thiocyanate, Fe(NCS)$_{2}$. Using magnetic susceptibility measurements on these materials and on cobalt (II) thiocyanate and nickel (II) thiocyanate, Co(NCS)$_{2}$ and Ni(NCS)$_{2}$, respectively, we identify significantly stronger net antiferromagnetic interactions between the earlier TM ions-a decrease in the Weiss constant, \theta, from 29 K for Ni(NCS)$_{2}$ to -115 K for Mn(NCS)$_{2}$-a consequence of more diffuse 3d orbitals, increased orbital overlap and increasing numbers of unpaired $\it{t}$$_{2g}$ electrons. We elucidate the magnetic structures of these materials: Mn(NCS)$_{2}$, Fe(NCS)$_{2}$ and Co(NCS)$_{2}$ order into the same antiferromagnetic commensurate ground state, whilst Ni(NCS)$_{2}$ adopts a ground state structure consisting of ferromagnetically ordered layers stacked antiferromagnetically. We show that magnetic molecular frameworks with significantly stronger net exchange interactions can be constructed by using earlier TMs.
- arXiv:2003.03594 (replaced) [pdf, ps, other]
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Title: Field-selective classical spin liquid and magnetization plateaus on kagome latticeComments: 7 pages, 7 figuresJournal-ref: J. Phys. Soc. Jpn. 89, 053708 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el); Materials Science (cond-mat.mtrl-sci); Statistical Mechanics (cond-mat.stat-mech)
We obtain a classical spin liquid (CSL) phase by applying a magnetic field in $J_1$-$J_2$-$J_3$ Ising model on a kagome lattice. As we proved in the previous study [Phys. Rev. Lett. {\bf 119}, 077207 (2017)], this model realizes one species of CSL, the hexamer CSL, at zero magnetic field, which consists of macroscopically degenerate spin configurations with mixed total magnetization, $M$. The magnetic field selects its subset, which can be mapped to a trimer covering of the dual lattice, and forms a magnetization plateau of $M=1/9$. In addition to this CSL, we find two other magnetization plateaus at $M=5/9$ and $17/27$, which are ascribed to the "multimer" superstructures on a dual lattice.
- arXiv:2003.03902 (replaced) [pdf, ps, other]
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Title: The Schwartz-Soffer and more inequalities for random fieldsComments: 14 pagesSubjects: Mathematical Physics (math-ph); Disordered Systems and Neural Networks (cond-mat.dis-nn)
A new series of correlation inequalities for random field spin systems is proven rigorously. First one corresponds to the well-known Schwartz-Soffer inequality. These are expected to rule out incorrect results calculated in effective theories and numerical studies. The large $N$ expansion with the replica method for random field systems as an example is checked by these inequalities. It is shown that several critical exponents of multiple-point correlation functions at critical point satisfy obtained inequalities.
- arXiv:2003.04015 (replaced) [pdf, other]
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Title: Superconducting mechanism for a new-type cuprate Ba$_2$CuO$_{3+δ}$ based on a multiorbital Lieb lattice modelAuthors: Kimihiro Yamazaki, Masayuki Ochi, Daisuke Ogura, Kazuhiko Kuroki, Hiroshi Eisaki, Shinichi Uchida, Hideo AokiComments: 19 pages, 20 figures, references updatedSubjects: Superconductivity (cond-mat.supr-con)
For a recently discovered new-type cuprate superconductor $\mathrm{Ba_{2}CuO_{3+\delta}}$, we propose a lattice structure which resembles the model considered by Lieb to represent the vastly oxygen-deficient material. We first investigate the stability of the Lieb-lattice structure, and then construct a multiorbital Hubbard model based on first-principles calculation. By applying the fluctuation-exchange approximation to the model and solving the linearized Eliashberg equation, we show that $s$-wave and $d$-wave pairings closely compete with each other, and, more interestingly, that the intra-orbital and inter-orbital pairings coexist. We further show that, if the energy of the $d_{3z^2-r^2}$ band is raised to make it "incipient" with the lower edge of the band close to the Fermi level within a realistic band filling regime, $s\pm$-wave superconductivity is strongly enhanced. We reveal an intriguing relation between the Lieb model and the two-orbital model for the usual K$_2$NiF$_4$ structure where a close competition between $s-$ and $d-$wave pairings is known to occur. The enhanced superconductivity in the present model is further shown to be related to an enhancement found previously in the bilayer Hubbard model with an incipient band.
- arXiv:2003.04612 (replaced) [pdf, other]
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Title: Bandgap engineering in an epitaxial two-dimensional honeycomb Si$_{6-x}$Ge$_x$ alloyAuthors: Antoine Fleurence, Yuto Awatani, Camille Huet, Frank B. Wiggers, Steaphan M. Wallace, Takahiro Yonezawa, Yukiko Yamada-TakamuraSubjects: Materials Science (cond-mat.mtrl-sci)
In this Letter, we demonstrate that it is possible to form a two-dimensional (2D) silicene-like Si$_5$Ge compound by replacing the Si atoms occupying on-top sites in the planar-like structure of epitaxial silicene on ZrB$_2$(0001) by deposited Ge atoms. For coverages below 1/6 ML, the Ge deposition gives rise to a Si$_{6-x}$Ge$_{x}$ alloy (with $x$ between 0 and 1) in which the on-top sites are randomly occupied by Si or Ge atoms. The progressive increase of the valence band maximum with $x$ observed experimentally originates from a selective charge transfer from Ge atoms to Si atoms. These achievements provide evidence for the possibility of engineering the bandgap in 2D SiGe alloys in a way that is similar for their bulk counterpart.
- arXiv:1712.09295 (replaced) [pdf, ps, other]
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Title: An operator-theoretical proof for the second-order phase transition in the BCS-Bogoliubov model of superconductivity (final version)Authors: Shuji WatanabeComments: Kyushu Journal of Mathematics, in press. arXiv admin note: substantial text overlap with arXiv:1607.00090, arXiv:1609.07224Journal-ref: Kyushu Journal of Mathematics 74 (2020), 177-196Subjects: Mathematical Physics (math-ph); Statistical Mechanics (cond-mat.stat-mech); Superconductivity (cond-mat.supr-con); Analysis of PDEs (math.AP)
We show that the transition from a normal conducting state to a superconducting state is a second-order phase transition in the BCS-Bogoliubov model of superconductivity from the viewpoint of operator theory. Here we have no magnetic field. Moreover we obtain the exact and explicit expression for the gap in the specific heat at constant volume at the transition temperature. To this end, we have to differentiate the thermodynamic potential with respect to the temperature two times. Since there is the solution to the BCS-Bogoliubov gap equation in the form of the thermodynamic potential, we have to differentiate the solution with respect to the temperature two times. Therefore, we need to show that the solution to the BCS-Bogoliubov gap equation is differentiable with respect to the temperature two times as well as its existence and uniqueness. We carry out its proof on the basis of fixed point theorems.
- arXiv:1806.03231 (replaced) [pdf, other]
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Title: Fluidity Onset in GrapheneAuthors: Denis A. Bandurin, Andrey V. Shytov, Leonid Levitov, Roshan Krishna Kumar, Alexey I. Berdyugin, Moshe Ben Shalom, Irina V. Grigorieva, Andre K. Geim, Gregory FalkovichComments: 8pgs, 4fgsJournal-ref: Nature Communications. 9, 4533, 2018Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Viscous electron fluids have emerged recently as a new paradigm of strongly-correlated electron transport in solids. Here we report on a direct observation of the transition to this long-sought-for state of matter in a high-mobility electron system in graphene. Unexpectedly, the electron flow is found to be interaction-dominated but non-hydrodynamic (quasiballistic) in a wide temperature range, showing signatures of viscous flows only at relatively high temperatures. The transition between the two regimes is characterized by a sharp maximum of negative resistance, probed in proximity to the current injector. The resistance decreases as the system goes deeper into the hydrodynamic regime. In a perfect darkness-before-daybreak manner, the interaction-dominated negative response is strongest at the transition to the quasiballistic regime. Our work provides the first demonstration of how the viscous fluid behavior emerges in an interacting electron system.
- arXiv:1811.11643 (replaced) [pdf, ps, other]
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Title: Bohmian mechanics for instrumentalistsAuthors: H. NikolicComments: 20 pages, version accepted for publication in Int. J. Quantum InfJournal-ref: Int. J. Quantum Inf. 17 (2019) 1950029Subjects: Quantum Physics (quant-ph); Other Condensed Matter (cond-mat.other); High Energy Physics - Phenomenology (hep-ph)
We formulate Bohmian mechanics (BM) such that the main objects of concern are macroscopic phenomena, while microscopic particle trajectories only play an auxiliary role. Such a formulation makes it easy to understand why BM always makes the same measurable predictions as standard quantum mechanics (QM), irrespectively of the details of microscopic trajectories. Relativistic quantum field theory (QFT) is interpreted as an effective long-distance theory that at smaller distances must be replaced by some more fundamental theory. Analogy with condensed-matter physics suggests that this more fundamental theory could have a form of non-relativistic QM, offering a simple generic resolution of an apparent conflict between BM and relativistic QFT.
- arXiv:1812.05690 (replaced) [pdf, other]
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Title: Vortex lattices and broken time reversal symmetry in the topological superconductor UPt3Authors: K. E. Avers, W. J. Gannon, S. J. Kuhn, W. P. Halperin, J. A. Sauls, L. DeBeer-Schmitt, C. D. Dewhurst, J. Gavilano, G. Nagy, U. Gasser, M. R. EskildsenComments: 7 pages plus 3 pages of supplementary materialJournal-ref: Nat. Phys. 16, 531-535 (2020)Subjects: Superconductivity (cond-mat.supr-con)
The topological superconductor UPt3, has three distinct vortex phases, a strong indication of its unconventional character. Using small-angle neutron scattering we have probed the vortex lattice in the UPt3 B phase with the magnetic field along the crystal c-axis. We find a difference in the vortex lattice configuration depending on the sign of the magnetic field relative to the field direction established upon entering the B phase at low temperature in a field sweep, showing that the vortices in this material posses an internal degree of freedom. This observation is facilitated by the discovery of a field driven non-monotonic vortex lattice rotation, driven by competing effects of the superconducting gap distortion and the vortex-core structure. From our bulk measurements we infer that the superconducting order parameter in the UPt3 B phase breaks time reversal symmetry and exhibits chiral symmetry with respect to the c-axis.
- arXiv:1812.07630 (replaced) [pdf, other]
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Title: Assessing the accuracy of direct-coupling analysis for RNA contact predictionComments: Supporting information included in ancillary filesJournal-ref: RNA 26, 637 (2020)Subjects: Quantitative Methods (q-bio.QM); Statistical Mechanics (cond-mat.stat-mech); Biological Physics (physics.bio-ph)
Many non-coding RNAs are known to play a role in the cell directly linked to their structure. Structure prediction based on the sole sequence is however a challenging task. On the other hand, thanks to the low cost of sequencing technologies, a very large number of homologous sequences are becoming available for many RNA families. In the protein community, it has emerged in the last decade the idea of exploiting the covariance of mutations within a family to predict the protein structure using the direct-coupling-analysis (DCA) method. The application of DCA to RNA systems has been limited so far. We here perform an assessment of the DCA method on 17 riboswitch families, comparing it with the commonly used mutual information analysis and with state-of-the-art R-scape covariance method. We also compare different flavors of DCA, including mean-field, pseudo-likelihood, and a proposed stochastic procedure (Boltzmann learning) for solving exactly the DCA inverse problem. Boltzmann learning outperforms the other methods in predicting contacts observed in high resolution crystal structures.
- arXiv:1901.07149 (replaced) [pdf, ps, other]
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Title: Spin Vortices and Skyrmions of a Single Electron in Inhomogeneous Magnetic FieldsJournal-ref: Phys. Rev. B 101, 115407 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Quantum Physics (quant-ph)
We study the spin textures of a confined two-dimensional electron in inhomogeneous magnetic fields. These fields can either be external or effective fields due to a background magnetic texture in the plane in which the electron resides. By analytical considerations, WKB-type approximations, and by performing numerical diagonalizations we show that the in-plane spin field components of a single electron can form vortices while the total spin field can become a skyrmion. Most interestingly, we find that topological trivial magnetic fields can induce topological spin field configurations in the eigenstates of the electron due to quantum effects.
- arXiv:1902.00042 (replaced) [pdf]
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Title: Coupling phenomena and collective effects in resonant meta-molecules supporting plasmonic and magnetic functionalities: a reviewAuthors: Nicolò MaccaferriSubjects: Materials Science (cond-mat.mtrl-sci)
We review both the fundamental aspects and the applications of functional magneto-optic and opto-magnetic metamaterials displaying collective and coupling effects on the nanoscale, where the concepts of optics and magnetism merge to produce unconventional phenomena. The use of magnetic materials instead of the usual noble metals allows for an additional degree of freedom for the control of electromagnetic field properties, as well as it allows light to interact with the spins of the electrons and to actively manipulate the magnetic properties of such nanomaterials. In this context, we explore the concepts of near-field coupling of plasmon modes in magnetic meta-molecules, as well as the effect of excitation of surface lattice resonances in magneto-plasmonic crystals. Moreover, we discuss how these coupling effects can be exploited to artificially enhance optical magnetism in plasmonic meta-molecules and crystals. Finally, we highlight some of the present challenges and provide a perspective on future directions of the research towards photon-driven fast and efficient nanotechnologies bridging magnetism and optics beyond current limits.
- arXiv:1902.09550 (replaced) [pdf, other]
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Title: $\textit{Ab Initio}$ Mismatched Interface Theory of Graphene on $α$-RuCl$_3$: Doping and MagnetismJournal-ref: Phys. Rev. Lett. 124, 106804 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el)
Recent developments in twisted and lattice-mismatched bilayers have revealed a rich phase space of van der Waals systems and generated excitement. Among these systems are heterobilayers which can offer new opportunities to control van der Waals systems with strong in plane correlations such as spin-orbit-assisted Mott insulator $\alpha$-RuCl$_3$. Nevertheless, a theoretical $\textit{ab initio}$ framework for mismatched heterobilayers without even approximate periodicity is sorely lacking. We propose a general strategy for calculating electronic properties of such systems, mismatched interface theory (MINT), and apply it to the graphene/$\alpha$-RuCl$_{3}$ (GR/$\alpha$-RuCl$_{3}$) heterostructure. Using MINT, we predict uniform doping of 4.77$\%$ from graphene to $\alpha$-RuCl$_3$ and magnetic interactions in $\alpha$-RuCl$_3$ to shift the system toward the Kitaev point. Hence we demonstrate that MINT can guide targeted materialization of desired model systems and discuss recent experiments on GR/$\alpha$-RuCl$_{3}$ heterostructures.
- arXiv:1903.01414 (replaced) [pdf, other]
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Title: Quantum Joule Expansion of One-Dimensional SystemsComments: 19 pages, 19 figuresJournal-ref: Phys. Rev. A 101, 033608 (2020)Subjects: Quantum Gases (cond-mat.quant-gas); Statistical Mechanics (cond-mat.stat-mech); Strongly Correlated Electrons (cond-mat.str-el); High Energy Physics - Lattice (hep-lat); Quantum Physics (quant-ph)
We investigate the Joule expansion of nonintegrable quantum systems that contain bosons or spinless fermions in one-dimensional lattices. A barrier initially confines the particles to be in half of the system in a thermal state described by the canonical ensemble and is removed at time $t = 0$. We investigate the properties of the time-evolved density matrix, the diagonal ensemble density matrix and the corresponding canonical ensemble density matrix with an effective temperature determined by the total energy conservation using exact diagonalization. The weights for the diagonal ensemble and the canonical ensemble match well for high initial temperatures that correspond to negative effective final temperatures after the expansion. At long times after the barrier is removed, the time-evolved R\'enyi entropy of subsystems bigger than half can equilibrate to the thermal entropy with exponentially small fluctuations. The time-evolved reduced density matrix at long times can be approximated by a thermal density matrix for small subsystems. Few-body observables, like the momentum distribution function, can be approximated by a thermal expectation of the canonical ensemble with strongly suppressed fluctuations. The negative effective temperatures for finite systems go to nonnegative temperatures in the thermodynamic limit for bosons, but is a true thermodynamic effect for fermions, which is confirmed by finite temperature density matrix renormalization group calculations. We propose the Joule expansion as a way to dynamically create negative temperature states for fermion systems with repulsive interactions.
- arXiv:1903.02335 (replaced) [pdf, other]
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Title: Global Delocalization Transition in the de Moura-Lyra ModelComments: 6 pages, 4 figures Submitted to Physical Review B on the 25th of March 2019Journal-ref: Physical Review B 99, 205148 (2019)Subjects: Disordered Systems and Neural Networks (cond-mat.dis-nn)
The possibility of having a delocalization transition in the 1D de Moura-Lyra class of models (having a power-spectrum $\propto q^{-\alpha})$ has been the object of a long standing discussion in the literature, filled with ambiguities. In this letter, we report the first numerical evidences that such a transition happens at $\alpha=1$, where the localization length (measured from the scaling of the conductance) is shown to diverge as $(1-\alpha)^{-1}$. The persistent finite-size scaling of the data is shown to be caused by a very slow convergence of the nearest-neighbor correlator to its infinite-size limit, and controlled by the choice of a proper scaling parameter. This last conclusion leads to the re-interpretation of the localization in these models to be caused by an effective Anderson uncorrelated model at small length-scales. Finally, the numerical results are confirmed by analytical perturbative calculations which are built on previous work.
- arXiv:1903.10468 (replaced) [pdf]
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Title: Strain Modulated Superlattices in GrapheneAuthors: R. Banerjee, V.-H. Nguyen, T. Granzier-Nakajima, L. Pabbi, A. Lherbier, A.R. Binion, J.-C. Charlier, M. Terrones, E.W. HudsonComments: 18 pages, 5 figures and supplementary informationSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci)
Strain engineering of graphene takes advantage of one of the most dramatic responses of Dirac electrons enabling their manipulation via strain-induced pseudo-magnetic fields. Numerous theoretically proposed devices, such as resonant cavities and valley filters, as well as novel phenomena, such as snake states, could potentially be enabled via this effect. These proposals, however, require strong, spatially oscillating magnetic fields while to date only the generation and effects of pseudo-gauge fields which vary at a length scale much larger than the magnetic length have been reported. Here we create a periodic pseudo-gauge field profile using periodic strain that varies at the length scale comparable to the magnetic length and study its effects on Dirac electrons. A periodic strain profile is achieved by pulling on graphene with extreme (>10%) strain and forming nanoscale ripples, akin to a plastic wrap pulled taut at its edges. Combining scanning tunneling microscopy and atomistic calculations, we find that spatially oscillating strain results in a new quantization different from the familiar Landau quantization observed in previous studies. We also find that graphene ripples are characterized by large variations in carbon-carbon bond length, directly impacting the electronic coupling between atoms, which within a single ripple can be as different as in two different materials. The result is a single graphene sheet that effectively acts as an electronic superlattice. Our results thus also establish a novel approach to synthesize an effective 2D lateral heterostructure - by periodic modulation of lattice strain.
- arXiv:1904.12552 (replaced) [pdf, other]
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Title: Linking invariant for the quench dynamics of a two-dimensional two-band Chern insulatorJournal-ref: Phys. Rev. A 101, 032104 (2020)Subjects: Quantum Gases (cond-mat.quant-gas)
We discuss the topological invariant in the (2+1)-dimensional quench dynamics of a two-dimensional two-band Chern insulator starting from a topological initial state (i.e., with a nonzero Chern number $c_i$), evolved by a post-quench Hamiltonian (with Chern number $c_f$). In contrast to the process with $c_i=0$ studied in previous works, this process cannot be characterized by the Hopf invariant that is described by the sphere homotopy group $\pi_3(S^2)=\mathbb{Z}$. It is possible, however, to calculate a variant of the Chern-Simons integral with a complementary part to cancel the Chern number of the initial spin configuration, which at the same time does not affect the (2+1)-dimensional topology. We show that the modified Chern-Simons integral gives rise to a topological invariant of this quench process, i.e., the linking invariant in the $\mathbb{Z}_{2c_i}$ class: $\nu = (c_f - c_i) \mod (2c_i)$. We give concrete examples to illustrate this result and also show the detailed deduction to get this linking invariant.
- arXiv:1905.09404 (replaced) [pdf, other]
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Title: Local Berry curvature signatures in dichroic angle-resolved photoelectron spectroscopyAuthors: Michael Schüler, Umberto De Giovannini, Hannes Hübener, Angel Rubio, Michael A. Sentef, Philipp WernerComments: 13 pages, 7 figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Topologically nontrivial two-dimensional materials hold great promise for next-generation optoelectronic applications. However, measuring the Hall or spin-Hall response is often a challenge and practically limited to the ground state. An experimental technique for tracing the topological character in a differential fashion would provide useful insights. In this work, we show that circular dichroism angle-resolved photoelectron spectroscopy (ARPES) provides a powerful tool which can resolve the topological and quantum-geometrical character in momentum space. In particular, we investigate how to map out the signatures of the local Berry curvature by exploiting its intimate connection to the orbital angular momentum. A spin-resolved detection of the photoelectrons allows to extend the approach to spin-Chern insulators. Our predictions are corroborated by state-of-the art \emph{ab initio} simulations employing time-dependent density functional theory, complemented with model calculations. The present proposal can be extended to address topological properties in materials out of equilibrium in a time-resolved fashion.
- arXiv:1908.10690 (replaced) [pdf, other]
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Title: Filtering the photoluminescence spectra of atomically thin semiconductors with grapheneAuthors: Etienne Lorchat, Luis E. Parra López, Cédric Robert, Delphine Lagarde, Guillaume Froehlicher, Takashi Taniguchi, Kenji Watanabe, Xavier Marie, Stéphane BerciaudSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci); Optics (physics.optics)
Atomically thin semiconductors made from transition metal dichalcogenides (TMDs) are model systems for investigations of strong light-matter interactions and applications in nanophotonics, opto-electronics and valley-tronics. However, the typical photoluminescence spectra of TMD monolayers display a large number of intrinsic and extrinsic features that are particularly challenging to decipher. On a practical level, monochromatic TMD-based emitters would be beneficial for low-dimensional devices but no solution has yet been found to meet this challenge. Here, using a counter-intuitive strategy that consists in interfacing TMD monolayers with graphene, a system known as an efficient luminescence quencher, we demonstrate bright, single and narrow-line photoluminescence arising solely from TMD neutral excitons. This observation stems from two effects: (i) complete neutralization of the TMD by the adjacent graphene leading to the absence of optical features from charged excitons (ii) selective non-radiative transfer of TMD excitons to graphene, that is sufficiently rapid to quench radiative recombination of long-lived excitonic species without significantly affecting bright excitons, which display much shorter, picosecond radiative lifetimes at low temperatures. Our approach is systematically applied to four tungsten and molybdenum-based TMDs and establishes TMD/graphene heterostructures as a unique set of opto-electronic building blocks. Graphene not only endows TMDs monolayers with superior optical performance and enhanced photostability but also provides an excellent electrical contact, suitable for TMD-based electroluminescent systems emitting visible and near-infrared photons at near THz rate with linewidths approaching the lifetime limit.
- arXiv:1909.06027 (replaced) [pdf, ps, other]
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Title: VI3: a 2D Ising ferromagnetComments: 7 pages, 8 figures, 2 tables, Phys. Rev. B Rapid, in pressJournal-ref: Phys. Rev. B 101, 100402 (2020)Subjects: Materials Science (cond-mat.mtrl-sci); Strongly Correlated Electrons (cond-mat.str-el)
Two-dimensional (2D) magnetic materials are of great current interest for their promising applications in spintronics. Here we propose the van der Waals (vdW) material VI3 to be a 2D Ising ferromagnet (FM), using density functional calculations, crystal field level diagrams, superexchange model analyses, and Monte Carlo simulations. The $a_{1g}$$^1$$e'_{-}$$^1$ ground state in the trigonal crystal field gives rise to the 2D Ising FM due to a significant single ion anisotropy (SIA) and enhanced FM superexchange both associated with the $S_z$=1 and $L_z$=--1 state of V3+ ions. We find that a tensile strain on the VI3 monolayer further stabilizes the $a_{1g}$$^1$$e'_{-}$$^1$ ground state, and its Curie temperature ($T_{\rm C}$) would increase from 70 K to 90-110 K under a 2.5-5\% tensile strain. Moreover, we suggest a group of spin-orbital states with a strong SIA which may help to search more 2D Ising magnets.
- arXiv:1910.01744 (replaced) [pdf, ps, other]
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Title: Microscopic foundations of the Second Law of Thermodynamics within Nonunitary Newtonian GravityComments: 2 figures, 8 pages. arXiv admin note: text overlap with arXiv:1801.02500Journal-ref: IJQI Vol. 17, No. 8 (2019) 1941006Subjects: Statistical Mechanics (cond-mat.stat-mech); Quantum Physics (quant-ph)
The quest for a microscopic foundation of Thermodynamics is addressed within the Nonunitary Newtonian Gravity model through the study of a specific closed system, namely a three-dimensional harmonic nanocrystal. A numerical calculation of the nanocrystal von Neumann entropy as a function of time is performed, showing a sharp monotonic increase, followed by a stabilization at late times. This behavior is consistent with the emergence of a micro-canonical ensemble within the initial energy levels, signaling, in this way, the establishment of a non-unitary gravity-induced thermal equilibrium.
- arXiv:1910.06644 (replaced) [pdf, other]
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Title: Mechanical transmission of rotational motion between molecular-scale gearsJournal-ref: Phys. Rev. Applied 13, 034024 (2020)Subjects: Soft Condensed Matter (cond-mat.soft); Chemical Physics (physics.chem-ph)
Manipulating and coupling molecule gears is the first step towards realizing molecular-scale mechanical machines. Here, we theoretically investigate the behavior of such gears using molecular dynamics simulations. Within a nearly rigid-body approximation we reduce the dynamics of the gears to the rotational motion around the orientation vector. This allows us to study their behavior based on a few collective variables. Specifically, for a single hexa (4-tert-butylphenyl) benzene molecule we show that the rotational-angle dynamics corresponds to the one of a Brownian rotor. For two such coupled gears, we extract the effective interaction potential and find that it is strongly dependent on the center of mass distance. Finally, we study the collective motion of a train of gears. We demonstrate the existence of three different regimes depending on the magnitude of the driving-torque of the first gear: underdriving, driving and overdriving, which correspond, respectively, to no collective rotation, collective rotation and only single gear rotation. This behavior can be understood in terms of a simplified interaction potential.
- arXiv:1910.13287 (replaced) [pdf]
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Title: Spin-flop transition in atomically thin MnPS$_3$ crystalsAuthors: Gen Long, Hugo Henck, Marco Gibertini, Dumitru Dumcenco, Zhe Wang, Takashi Taniguchi, Kenji Watanabe, Enrico Giannini, Alberto F. MorpurgoComments: 19 pages, 4 figures + supplementary (10 pages, 5 figures)Journal-ref: Nano Lett. 20, 2452-2459 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
The magnetic state of atomically thin semiconducting layered antiferromagnets such as CrI$_3$ and CrCl$_3$ can be probed by forming tunnel barriers and measuring their resistance as a function of magnetic field ($H$) and temperature ($T$). This is possible because the tunneling magnetoresistance originates from a spin-filtering effect sensitive to the relative orientation of the magnetization in different layers, i.e., to the magnetic state of the multilayers. For systems in which antiferromagnetism occurs within an individual layer, however, no spin-filtering occurs: it is unclear whether this strategy can work. To address this issue, we investigate tunnel transport through atomically thin crystals of MnPS$_3$, a van der Waals semiconductor that in the bulk exhibits easy-axis antiferromagnetic order within the layers. For thick multilayers below $T\simeq 78$ K, a $T$-dependent magnetoresistance sets-in at $\sim 5$ T, and is found to track the boundary between the antiferromagnetic and the spin-flop phases known from bulk magnetization measurements. The magnetoresistance persists down to individual MnPS$_3$ monolayers with nearly unchanged characteristic temperature and magnetic field scales, albeit with a different dependence on $H$. We discuss the implications of these finding for the magnetic state of atomically thin MnPS$_3$ crystals, conclude that antiferromagnetic correlations persist down to the level of individual monolayers, and that tunneling magnetoresistance does allow magnetism in 2D insulating materials to be detected even in the absence of spin-filtering.
- arXiv:1911.05261 (replaced) [pdf]
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Title: Two-Dimensional Si-Ge Monolayers: Stabilities, Structures and Electronic PropertiesComments: 23 pages, 5 figuresJournal-ref: Journal of Applied Physics 127, 094302 (2020)Subjects: Materials Science (cond-mat.mtrl-sci)
Si-Ge monolayers (SiGeM) with different elementary proportion x (0<x<1) were systematically studied for the first-time using ab initio calculations in this work. The structural stabilities of the Si1-xGexM with different symmetries were investigated using phonon spectra, and an infinite miscibility between Si and Ge elements were revealed in the 2D honeycomb structures. The simulated scanning tunneling microscope images and Raman and infrared active modes of the Si1-xGexM were then obtained for structural characterizations. Interestingly, the study of electronic properties revealed not previously reported oscillatory nonlinear dependence of band gap values on the elementary proportion x in the Si1-xGexM, which suggests an alternative way for tuning the band gaps of 2D materials. Additionally, low effective masses (0.008m0 ~ 0.021m0) of the carriers in the semiconducting Si1-xGexM were found, which has potentials for high-speed applications. Considering the advantage of their compatibility with current Si-based technology and the trend of miniature of electronic devices, the Si1-xGexM with stable structures and excellent properties would be important for 2D applications based on group IV materials.
- arXiv:1911.07777 (replaced) [pdf]
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Title: Raman laser from an optical resonator with a grafted single molecule monolayerComments: main text and SI included; accepted to Nature Photonics in 2019Subjects: Optics (physics.optics); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Applied Physics (physics.app-ph)
Raman-based technologies have enabled many ground-breaking scientific discoveries related to surface science, single molecule chemistry and biology. For example, researchers have identified surface bound molecules by their Raman vibrational modes and demonstrated polarization-dependent Raman gain. However, a surface constrained Raman laser has yet to be demonstrated because of the challenges associated with achieving a sufficiently high photon population located at a surface to transition from spontaneous to stimulated Raman scattering. Here, advances in surface chemistry and in integrated photonics are combined to demonstrate lasing based on surface stimulated Raman scattering (SSRS). By creating an oriented, constrained Si-O-Si monolayer on the surface of integrated silica optical microresonators, the requisite conditions for SSRS are achieved with low threshold powers (200microW). The expected polarization-dependence of the SSRS due to the orientation of the Si-O-Si bond is observed. Due to the ordered monolayer, the Raman lasing efficiency is improved from ~5% to over 40%.
- arXiv:1912.08943 (replaced) [pdf]
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Title: New interaction potentials for borate glasses with mixed network formersJournal-ref: Journal of Chemical Physics (Vol.152, Issue 10) 2020Subjects: Computational Physics (physics.comp-ph); Disordered Systems and Neural Networks (cond-mat.dis-nn); Materials Science (cond-mat.mtrl-sci)
We adapt and apply a recently developed optimization scheme used to obtain effective potentials for aluminosilicate glasses to include the network former boron into the interaction parameter set. As input data for the optimization, we used the radial distribution functions of the liquid at high temperature generated by ab initio molecular dynamics simulations, and density, coordination and elastic modulus of glass at room temperature from experiments. The new interaction potentials are shown to reproduce reliably the structure, coordination and mechanical properties over a wide range of compositions for binary alkali borates. Furthermore, the transferability of these new interaction parameters allows mixing to reliably reproduce properties of various boroaluminate and borosilicate glasses.
- arXiv:1912.09352 (replaced) [pdf]
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Title: Silicon-vacancy color centers in phosphorus-doped diamondAuthors: Assegid Mengistu Flatae, Stefano Lagomarsino, Florian Sledz, Navid Soltani, Shannon S. Nicley, Ken Haenen, Robert Rechenberg, Michael F. Becker, Silvio Sciortino, Nicla Gelli, Lorenzo Giuntini, Francesco Taccetti, Mario AgioSubjects: Applied Physics (physics.app-ph); Materials Science (cond-mat.mtrl-sci); Quantum Physics (quant-ph)
The controlled creation of color centers in phosphorus-doped (n-type) diamond can facilitate the electronics integration of quantum photonics devices, such as single-photon sources operating upon electrical injection. Silicon vacancy (SiV) color centers are promising candidates, but so far the conditions for single-photon emission in phosphorus-doped diamond have not been investigated. In this study, we create SiV color centers in diamond samples with different phosphorus concentrations and show that the fluorescence background due to doping, nitrogen-impurities and ion implantation induced defects can be significantly suppressed. Single-photon emitters in phosphorus-doped diamond are obtained at the low Si-ion implantation fluences.
- arXiv:1912.13164 (replaced) [pdf, other]
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Title: Magnetization reversal of dipolar coupled nanomagnets studied by two-dimensional electron gas based micro-Hall magnetometryAuthors: N. Keswani, Y. Nakajima, N. Chauhan, H. Chakraborti, K. Dasgupta, S. Kumar, Y. Ohno, H. Ohno, P. DasComments: 5 pages, 4 figuresJournal-ref: Appl. Phys. Lett. 116, 102401 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We report here the results of two-dimensional electron gas based micro-Hall magnetometry measurements and micromagnetic simulations of dipolar coupled nanomagnets of Ni80Fe20 arranged in a double ring-like geometry. We observe that although magnetic force microscopy images exhibit single domain like magnetic states for the nanostructures, their reversal processes may undergo complex behavior. The details of such reversal behavior is observed as specific features in micro-Hall magnetometry data which compares well with the micromagnetic simulation data.
- arXiv:2001.00479 (replaced) [pdf, other]
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Title: Thresholds of descending algorithms in inference problemsComments: 8 pages, 4 figuresJournal-ref: J. Stat. Mech. (2020) 034004Subjects: Machine Learning (cs.LG); Disordered Systems and Neural Networks (cond-mat.dis-nn); Machine Learning (stat.ML)
We review recent works on analyzing the dynamics of gradient-based algorithms in a prototypical statistical inference problem. Using methods and insights from the physics of glassy systems, these works showed how to understand quantitatively and qualitatively the performance of gradient-based algorithms. Here we review the key results and their interpretation in non-technical terms accessible to a wide audience of physicists in the context of related works.
- arXiv:2001.06205 (replaced) [pdf, other]
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Title: Discovering topological surface states of Dirac pointsComments: 14 pages, 8 figures, 5 tablesJournal-ref: Phys. Rev. Lett. 124, 104301 (2020)Subjects: Materials Science (cond-mat.mtrl-sci); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Dirac materials, unlike the Weyl materials, have not been found in experiments to support intrinsic topological surface states, as the surface arcs in existing systems are unstable against symmetry-preserving perturbations. Utilizing the proposed glide and time-reversal symmetries, we theoretically design and experimentally verify an acoustic crystal of two frequency-isolated three-dimensional Dirac points with $Z_2$ monopole charges and four gapless helicoid surface states.
- arXiv:2002.08047 (replaced) [pdf, ps, other]
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Title: Nonequilibrium effects in the Casimir force between two similar metallic plates kept at different temperaturesComments: 18 pages, 1 table, 6 figures; accepted for publication in Phys. Rev. AJournal-ref: Phys. Rev. A 101, 032506 (2020)Subjects: Quantum Physics (quant-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We study the Casimir pressure between two similar plates of finite thickness kept at different temperatures in the case when the dielectric permittivity of the plates depends on temperature. It is suggested to consider the dielectric permittivity at two different temperatures as the permittivities of two dissimilar bodies, thus allowing to apply the theory of Casimir forces out of thermal equilibrium developed earlier in the literature. Following this approach, we show that, in addition to the equilibrium contribution to the nonequilibrium Casimir pressure, a proper nonequilibrium contribution arises for temperature-dependent dielectric permittivities. Furthermore, the equilibrium contribution in this case does not equal the mean of the equilibrium Casimir pressures at the temperatures of the plates. As an application, the total nonequilibrium Casimir pressure between two gold plates and between two titanium plates is calculated as a function of the plate thickness and their separation, using the Drude and the plasma model. For plate separations ranging from 0.5 to 2 micrometers, the relative difference between the theoretical predictions for these two models reaches 39%. The proper nonequilibrium term may be as large as 4% of the magnitude of the total nonequilibrium pressure.
- arXiv:2002.10753 (replaced) [pdf]
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Title: Bias-field-free spin Hall nano-oscillators with an out-of-plane precession modeJournal-ref: J. Appl. Phys. 127, 103904 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Spin Hall nano-oscillators (SHNOs) are promising candidates for new microwave oscillators with high durability due to a small driving current. However, conventional SHNOs with an in-plane precession (IPP) mode require a bias field for stable oscillations which is not favored in certain applications such as neuromorphic computing. Here, we propose and theoretically analyze a bias-field-free SHNO with an in-plane hard axis and an out-of-plane precession (OPP) mode by solving the Landau-Lifshitz-Gilbert (LLG) equation analytically and numerically. We derive formulas for driving currents and precession frequency, and show that they are in good agreement with numerical simulation results. We show that our proposed SHNOs can be driven by much smaller bias current than conventional spin torque nano-oscillators.
Crosses
- arXiv:2002.06088 (cross-list from cond-mat.quant-gas) [pdf, other]
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Title: Phase Diagram of Solitons in the Polar Phase of a Spin-1 Bose-Einstein CondensateSubjects: Quantum Gases (cond-mat.quant-gas); Other Condensed Matter (cond-mat.other)
We theoretically study the structure of a stationary soliton in the polar phase of spin-1 Bose--Einstein condensate in the presence of quadratic Zeeman effect at zero temperature. The phase diagram of such solitons is mapped out by finding the states of minimal soliton energy in the defining range of polar phase. The states are assorted into normal, anti-ferromagnetic, broken-axisymmetry, and ferromagnetic phases according to the number and spin densities in the core. The order of phase transitions between different solitons and the critical behaviour of relevant continuous transitions are proved within the mean-field theory.
Fri, 13 Mar 2020
- arXiv:2003.05453 [pdf, other]
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Title: Topology and edge states survive quantum criticality between topological insulatorsAuthors: Ruben VerresenComments: 4 pages + appendixSubjects: Strongly Correlated Electrons (cond-mat.str-el); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); High Energy Physics - Theory (hep-th); Quantum Physics (quant-ph)
It is often thought that emergent phenomena in topological phases of matter are destroyed when tuning to a critical point. In particular, topologically protected edge states supposedly delocalize when the bulk correlation length diverges. We show that this is not true in general. Edge states of topological insulators or superconductors remain exponentially localized---despite a vanishing band gap---if the transition increases the topological index. This applies to all classes where the topological classification is larger than $Z_2$, notably including Chern insulators. Moreover, these edge states are stable to disorder, unlike in topological semi-metals. This new phenomenon is explained by generalizing band (or mass) inversion---a unifying perspective on topological insulators---to kinetic inversion. In the spirit of the bulk-boundary correspondence, we also identify topological invariants at criticality, which take half-integer values and separate topologically-distinct universality classes by a multi-critical point. This work enlarges the scope of topological protection and stability by showing that bulk energy gaps can be unnecessary. Experimental probes and stability to interactions are discussed.
- arXiv:2003.05465 [pdf, other]
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Title: Characterization of solvable spin models via graph invariantsComments: 19 pages, 4 tables, 5 figuresSubjects: Quantum Physics (quant-ph); Strongly Correlated Electrons (cond-mat.str-el)
Exactly solvable models are essential in physics. For many-body spin-1/2 systems, an important class of such models consists of those that can be mapped to free fermions hopping on a graph. We provide a complete characterization of models which can be solved this way. Specifically, we reduce the problem of recognizing such spin models to the graph-theoretic problem of recognizing line graphs, which has been solved optimally. A corollary of our result is a complete set of constant-sized commutation structures that constitute the obstructions to a free-fermion solution. We find that symmetries are tightly constrained in these models. Pauli symmetries correspond to either: (i) cycles on the fermion hopping graph, (ii) the fermion parity operator, or (iii) logically encoded qubits. Clifford symmetries within one of these symmetry sectors, with three exceptions, must be symmetries of the free-fermion model itself. We demonstrate how several exact free-fermion solutions from the literature fit into our formalism and give an explicit example of a new model previously unknown to be solvable by free fermions.
- arXiv:2003.05468 [pdf, other]
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Title: A comparison of two different mechanisms for deterministic spin orbit torque magnetization switchingSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
In this article we analyze by modeling two possible mechanisms for magnetization switching using spin orbit torques, which have been reported to cause field-free deterministic switching in experiments. Here we compare the field-free magnetization switching due to a tilt of the anisotropy direction against the use of an antiferromagnetic bias field. Simple results obtained analytically show that a bias field not only causes the magnetization reversal but also reduces the corresponding energy barrier. The critical current required for magnetization switching is analyzed on the basis of a macrospin model. It is shown that although the field-free deterministic switching caused by a tilt of the anisotropy is more robust than the bias field in the development of memory elements, a compromise between requirements has to be adopted when selecting the parameters for specific applications.
- arXiv:2003.05494 [pdf]
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Title: A Spin-polarized two dimensional electron gas at the EuTiO$_{3}$(001) surfaceAuthors: R. Di Capua, M. Radovic, N. C. Plumb, J. H. Dil, Z. Ristic, E. B. Guedes, G. M. De Luca, Z. Wang, M. Verma, A. P. Weber, R. Pentcheva, M. SalluzzoComments: Main text: 15 pages, 4 figures; Supplementary Materials: 7 pages, 6 figuresSubjects: Materials Science (cond-mat.mtrl-sci)
The discovery of a surface/interfacial quasi 2-dimensional electron gas (q2DEG) in SrTiO$_{3}$ boosted expectations for novel oxide electronics due the intriguing and rich physics uncovered, including multiband and possibly unconventional superconductivity, large Rashba-like spin-orbit coupling and large spin to charge conversion efficiency. While magnetic effects have been reported, several studies attributed them to weak-(para)magnetism induced by extrinsic defects, such as oxygen vacancies. Here, by using in-situ high-resolution angle resolved photoemission we demonstrate that EuTiO$_{3}$, the magnetic counterpart of SrTiO$_{3}$, hosts a q2DEG at its (001) surface characterized by distinctive features reproduced by ab-initio calculations. In particular, we find that the exchange coupling between localized and delocalized Ti 3d electrons and magnetic Eu 4f states favors a robust ferromagnetic ground state. The results establish EuTiO3 as a new material platform for spin-polarized oxide q2DEGs.
- arXiv:2003.05506 [pdf, other]
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Title: High Thermoelectric Performance in Multi-pocketed Full-Heuslers and Their Defect EnergeticsSubjects: Materials Science (cond-mat.mtrl-sci)
This study, utilizing high-fidelity methods for computing electron-phonon scattering rates, theoretically demonstrates that ultrahigh intrinsic bulk thermoelectric performance across cryogenic-to-high temperatures is physically possible. It also demonstrates the benefit of accidental band degeneracy to thermoelectric performance is conditional upon their characters. Full-Heusler Sr$_{2}$BiAu featuring ten energy-aligned dispersive pockets (six along $\Gamma-X$ and four at $L$) is herein predicted to be theoretically capable of delivering $zT=0.4-4.9$ at $100-700$ K. Relative to the previously investigated Ba$_{2}$BiAu, the additional $L$-pockets in Sr$_{2}$BiAu significantly increase the power factor at low temperatures, as high as 12 mW m$^{-1}$ K$^{-2}$ near room temperature. As temperature rises, the performance decays quickly and sinks below that of Ba$_{2}$BiAu due to the differing dispersion and scattering characteristics of the $L$ and $\Gamma-X$ states. Sr$_{2}$SbAu is generally projected to deliver worse performance due to the appreciable energy-misalignment in the two accessible band pockets. The dominant intrinsic defect at play is Bi/Sb$_{\text{Au}}$ antisites, which limit the $n$-dopabilities of all of the Heusler compounds. Calculations suggest only Sr$_{2}$SbAu potentially has both a large enough stability region and high enough Sb$_{\text{Au}}$ antisite formation energies to retain some small chance at experimental realization as a high-performing thermoelectric.
- arXiv:2003.05518 [pdf, other]
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Title: Sub-nanoscale atom-by-atom crafting of skyrmion-defect interaction profilesComments: 32 pages, 7 figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Magnetic skyrmions are prime candidates as information carriers for spintronic devices due to their topological nature and nanometric size. However, unavoidable inhomogeneities inherent to any material leads to pinning or repulsion of skyrmions that, in analogy to biology concepts, define the phenotype of the skyrmion-defect interaction, generating complexity in their motion and challenging their application as future bits of information. Here, we demonstrate that atom-by-atom manufacturing of multi-atomic defects, being antiferromagnetic or ferromagnetic, permits the breeding of their energy profiles, for which we build schematically a Punnet-square. As established from first-principles for skyrmions generated in PdFe bilayer on Ir(111) surface, the resulting interaction phenotype is rich. It can be opposite to the original one and eventually be of dual pinning-repulsive nature yielding energy landscapes hosting multi-domains. This is dictated by the stacking site, geometry, size and chemical nature of the adsorbed defects, which control the involved magnetic interactions. This work provides new insights towards the development of disruptive device architectures incorporating defects into their design aiming to control and guide skyrmions.
- arXiv:2003.05524 [pdf, other]
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Title: Locality and Conservation Laws: How, in the presence of symmetry, locality restricts realizable unitariesAuthors: Iman MarvianComments: 5 pages+ 7 pages of Supplementary Material, 1 figure, preliminary version, comments welcomeSubjects: Quantum Physics (quant-ph); Statistical Mechanics (cond-mat.stat-mech); High Energy Physics - Theory (hep-th); Mathematical Physics (math-ph); Chaotic Dynamics (nlin.CD)
According to an elementary result in quantum computing, any unitary transformation on a composite system can be generated using 2-local unitaries, i.e., those which act only on two subsystems. Beside its fundamental importance in quantum computing, this result can also be regarded as a statement about the dynamics of systems with local Hamiltonians: although locality puts various constraints on the short-term dynamics, it does not restrict the possible unitary evolutions that a composite system with a general local Hamiltonian can experience after a sufficiently long time. We ask if such universality remains valid in the presence of conservation laws and global symmetries. In particular, can k-local symmetric unitaries on a composite system generate all symmetric unitaries on that system? Interestingly, it turns out that the answer is negative in the case of continuous symmetries, such as U(1) and SO(3): unless there are interactions which act non-trivially on every subsystem in the system, some symmetric unitaries cannot be implemented using symmetric Hamiltonians. In fact, the difference between the dimensions of the Lie algebra of all symmetric Hamiltonians and its subalgebra generated by k-local symmetric Hamiltonians with a fixed k, constantly increases with the system size (i.e., the number of subsystems). On the other hand, in the case of group U(1), we find that this no-go theorem can be circumvented if one is allowed to use a pair of ancillary qubits. In particular, any unitary which is invariant under rotations around z, can be implemented using Hamiltonians XX+YY and local Z on qubits. We discuss some implications of these results in the context of quantum thermodynamics and quantum computing.
- arXiv:2003.05529 [pdf, ps, other]
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Title: Computing LDOS resonance energy shifts of monatomic doped chainsComments: 2 figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Other Condensed Matter (cond-mat.other)
An analytical method to compute the LDOS energy spectrum and stationary states for finite size doped monatomic chains modelled by an effective one-dimensional tight-binding hamiltonian is presented. It is based on the formal solution of linear second order recurrence relations. We also study the LDOS energy spectrum of some doped monatomic chains applying a perturbative approach to the characteristic equation of the reference metallic structure doped with a few extraneous atoms.
- arXiv:2003.05539 [pdf, other]
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Title: Highly tunable magnetic coupling in ultrathin topological insulator films due to impurity resonancesSubjects: Materials Science (cond-mat.mtrl-sci); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We theoretically investigate the exchange interaction between magnetic impurities in ultrathin Bi$_2$Se$_3$ topological insulator films by taking into account the low-energy states produced by the impurities. We find that the locally induced impurity resonances strongly influence the exchange interaction between magnetic moments. In particular, we find a non-collinear alignment being more favorable than the collinear ferromagnetic alignment preferred when impurity states are ignored and only the pristine topological insulator band structure is considered. Moreover, we show that by applying of an electric field perpendicular to the ultrathin film, the exchange interaction can be drastically enhanced. This opens for the possibility of highly tunable magnetism by electric field.
- arXiv:2003.05540 [pdf, ps, other]
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Title: Finite-temperature many-body perturbation theory in the grand canonical ensembleSubjects: Chemical Physics (physics.chem-ph); Statistical Mechanics (cond-mat.stat-mech)
A finite-temperature many-body perturbation theory is presented that expands in power series the electronic grand potential, chemical potential, internal energy, and entropy on an equal footing. Sum-over-states and sum-over-orbitals analytical formulas for the second-order perturbation corrections to these thermodynamic properties are obtained in a time-independent, nondiagrammatic, algebraic derivation, relying on the sum rules of the Hirschfelder-Certain degenerate perturbation energies in a degenerate subspace as well as nine algebraic identities for zeroth-order thermal averages of one- through four-indexed quantities and of products thereof. They reproduce numerically exactly the benchmark data obtained as the numerical derivatives of the thermal-full-configuration-interaction results for a wide range of temperature.
- arXiv:2003.05553 [pdf, other]
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Title: A weight-dependent local correlation density-functional approximation for ensemblesComments: 13 pages, 8 figures, supporting information availableJournal-ref: J. Chem. Phys. 152, 214101 (2020)Subjects: Chemical Physics (physics.chem-ph); Materials Science (cond-mat.mtrl-sci); Strongly Correlated Electrons (cond-mat.str-el); Computational Physics (physics.comp-ph)
We report a local, weight-dependent correlation density-functional approximation that incorporates information about both ground and excited states in the context of density-functional theory for ensembles (eDFT). This density-functional approximation for ensembles is specially designed for the computation of single and double excitations within Gross--Oliveira--Kohn (GOK) DFT (i.e., eDFT for neutral excitations), and can be seen as a natural extension of the ubiquitous local-density approximation in the context of ensembles. The resulting density-functional approximation, based on both finite and infinite uniform electron gas models, automatically incorporates the infamous derivative discontinuity contributions to the excitation energies through its explicit ensemble weight dependence. Its accuracy is illustrated by computing single and double excitations in one-dimensional many-electron systems in the weak, intermediate and strong correlation regimes. Although the present weight-dependent functional has been specifically designed for one-dimensional systems, the methodology proposed here is general, i.e., directly applicable to the construction of weight-dependent functionals for realistic three-dimensional systems, such as molecules and solids.
- arXiv:2003.05558 [pdf, other]
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Title: Wave Turbulence in Self-Gravitating Bose GasesComments: 17 pages, 4 figuresSubjects: Statistical Mechanics (cond-mat.stat-mech); Quantum Gases (cond-mat.quant-gas); Fluid Dynamics (physics.flu-dyn)
We develop the theory of weak wave turbulence in systems described by the Schr\"odinger-Helmholtz equation in two and three dimensions. This model contains as limits both the familiar cubic nonlinear Schr\"odinger equation, and the Schr\"odinger-Newton equations, the latter being a nonrelativistic model of Fuzzy Dark Matter which has a nonlocal gravitational self-potential. We show that in the weakly-nonlinear limit the Schr\"odinger-Helmholtz equation has a simultaneous inverse cascade of particles and a forward cascade of energy. The inverse cascade we interpret as a nonequilibrium condensation process, which could be a precursor to collapses and structure formation at large scales (for example the formation of galactic dark matter haloes). We show that for the Schr\"odinger-Newton equation in two and three dimensions, and in the two-dimensional nonlinear Schr\"odinger equation, the particle and energy fluxes are carried by small deviations from thermodynamic distributions, rather than the Kolmogorov-Zakharov cascades that are familiar in wave turbulence. We develop a differential approximation model to characterise such "warm cascade" states.
- arXiv:2003.05566 [pdf, ps, other]
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Title: Ion Modes in Dense Ionized Plasmas through Non-Adiabatic Molecular DynamicsComments: 5 pages and 4 figures in the main manuscript, 6 pages and 9 figures in the supplementary information; typos corrected; corrected grammar, references fixed, author name adjustedSubjects: Plasma Physics (physics.plasm-ph); Statistical Mechanics (cond-mat.stat-mech); Computational Physics (physics.comp-ph)
We perform non-adiabatic simulations of warm dense aluminum based on the electron-force field (EFF) variant of wave-packet molecular dynamics. Comparison of the static ion-ion structure factor with density functional theory is used to validate the technique across a range of temperatures and densities spanning the warm dense matter regime. Differences in the dynamic structure factor and dispersion relation between adiabatic and non-adiabatic techniques suggest that the explicit inclusion of electrons is necessary to fully capture the low frequency dynamics of the response function.
- arXiv:2003.05567 [pdf, ps, other]
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Title: Geometrical Formulation of Adiabatic Pumping as a Heat EngineComments: 7 pages, 7 figuresSubjects: Statistical Mechanics (cond-mat.stat-mech)
We investigate a heat engine under an adiabatic (Thouless) pumping process. In this process, the extracted work and lower bound on dissipated availability are characterized by a vector potential and a Riemannian metric, respectively. We derive a trade-off relation between the power and effective efficiency. We also explicitly calculate the trade-off relation as well as the power and efficiency for a spin-boson model coupled to two reservoirs.
- arXiv:2003.05596 [pdf]
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Title: Nanoscale imaging of unusual photo-acoustic waves in thin flake VTe$_2$Authors: A. Nakamura, T. Shimojima, Y. Chiashi, M. Kamitani, H. Sakai, S. Ishiwata, H. Li, K. IshizakaComments: 6 pages, 5 figuresSubjects: Materials Science (cond-mat.mtrl-sci)
Controlling acoustic phonons, the carriers of sound and heat, has been attracting great attention toward the manipulation of sonic and thermal properties in nanometric devices. In particular, the photo-acoustic effect using ultrafast optical pulses has a promising potential to optically manipulate phonons in picoseconds time regime. However, its mechanism has been so far mostly based on the commonplace thermoelastic expansion in isotropic media, limiting the spectrum of potential applications. We investigate a conceptually new mechanism of photo-acoustic effect involving the structural instability, by utilizing a transition-metal dichalcogenide VTe$_2$ with the ribbon-type charge-density-wave (CDW). Ultrafast electron microscope imaging and diffraction measurements reveal the generation and propagation of unusual acoustic waves in the nanometric thin plate associated with the optically induced instantaneous charge-density-wave dissolution. Our results highlight the capability of photo-induced structural instability as a source of coherent acoustic waves.
- arXiv:2003.05598 [pdf]
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Title: Tetragonality induced superconductivity in anti-ThCr$_2$Si$_2$-type $RE_2$O$_2$Bi ($RE$ = rare earth) with Bi square netAuthors: Ryosuke Sei, Hideyuki Kawasoko, Kota Matsumoto, Masato Arimitsu, Kyohei Terakado, Daichi Oka, Shintaro Fukuda, Noriaki Kimura, Hidetaka Kasai, Eiji Nishibori, Kenji Ohoyama, Akinori Hoshikawa, Toru Ishigaki, Tetsuya Hasegawa, Tomoteru FukumuraJournal-ref: Dalton Trans. 49, 3321-3325 (2020)Subjects: Superconductivity (cond-mat.supr-con); Materials Science (cond-mat.mtrl-sci)
We report a series of layered superconductors, anti-ThCr$_2$Si$_2$-type $RE_2$O$_2$Bi ($RE$ = rare earth), composed of electrically conductive Bi square nets and magnetic insulating $RE_2$O$_2$ layers. The superconductivity was induced by separating Bi square nets as a result of excess oxygen incorporation, irrespective of the presence of magnetic ordering in $RE_2$O$_2$ layers. Intriguingly, the transition temperature of all $RE_2$O$_2$Bi including nonmagnetic Y$_2$O$_2$Bi was approximately scaled by the unit cell tetragonality ($c$/$a$), implying a key role of relative separation of the Bi square nets to induce the superconductivity.
- arXiv:2003.05600 [pdf]
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Title: First-Principles Exploration of Defect-Pairs in GaNComments: 18 pages, 5 figuresSubjects: Materials Science (cond-mat.mtrl-sci); Computational Physics (physics.comp-ph)
Using first-principles calculations, we explored all the 21 defect-pairs in GaN and considered 6 configurations with different defect-defect distances for each defect-pair. 15 defect-pairs with short defect-defect distances are found to be stable during structural relaxation, so they can exist in the GaN lattice once formed during the irradiation of high-energy particles. 9 defect-pairs have formation energies lower than 10 eV in the neutral state. The vacancy-pair VN-VN is found to have very low formation energies, as low as 0 eV in p-type and Ga-rich GaN, and act as efficient donors producing two deep donor levels, which can limit the p-type doping and minority carrier lifetime in GaN. VN-VN has been overlooked in the previous study of defects in GaN. Most of these defect-pairs act as donors and produce a large number of defect levels in the band gap. Their formation energies and concentrations are sensitive to the chemical potentials of Ga and N, so their influences on the electrical and optical properties of Ga-rich and N-rich GaN after irradiation should differ significantly. These results about the defect-pairs provide fundamental data for understanding the radiation damage mechanism in GaN and simulating the defect formation and diffusion behavior under irradiation.
- arXiv:2003.05608 [pdf, other]
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Title: A numerical method for inextensible elastic filaments in viscous fluidsSubjects: Fluid Dynamics (physics.flu-dyn); Soft Condensed Matter (cond-mat.soft); Biological Physics (physics.bio-ph)
The deformations of flagella are important in the motility of single- and multi-flagellated bacteria. Existing numerical methods have treated flagella as extensible filaments with a large extensional modulus, resulting in a stiff numerical problem and long simulation times. However, flagella are nearly inextensible, so to avoid large extensional stiffness, we introduce inextensible elastic rod models with hydrodynamics treated by a surface distribution of regularized Stokeslets. We benchmark this new model against previously described models of extensible elastic rods with hydrodynamics treated by a centerline distribution of regularized Stokeslets and rotlets, as well as a surface distribution of regularized Stokeslets. We compare the accuracy of the inextensible model with the extensible models and illustrate for which ratios of stretching/bending stiffness (which depend on the diameter of filament) the inextensible model is accurate and more efficient. We show that our inextensible approach can be markedly more efficient than the extensible models for many biological filaments. We also compare the accuracy of the centerline distribution of the Stokeslets and rotlets to the more accurate surface distribution of Stokeslets for modeling fluid-structure interactions of filaments.
- arXiv:2003.05609 [pdf]
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Title: Temperature and Rate Dependent Constitutive Behaviors of Low Melt Field's MetalSubjects: Materials Science (cond-mat.mtrl-sci)
Low melting point metals such as Field's metal and gallium are increasingly used as transition phases in stiffness-tuning soft materials and devices. Nevertheless, there is a knowledge gap on the fundamental constitutive behaviors of metals with melting points below 100 degree. This letter reports the stress-strain relationships of Field's metal at various temperatures and strain rates. This metal has the lowest melting point among metals whose constitutive behaviors have been studied systematically. Experimental results indicate that Field's metal exhibits a strain-softening behavior, in oppose to the strain-hardening behaviors of most engineering metals and alloys. A modified Johnson-Cook model is devised in this letter to describe the constitutive behaviors of Field's metal. The proposed metal will facilitate the design and analysis of functional materials and structures consisting of Field's metal.
- arXiv:2003.05612 [pdf]
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Title: Blocking temperature of a system of core/shell nanoparticlesSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
A theoretical study was conducted of the size dependence of the blocking temperature of a system of interacting core/shell nanoparticles. A method for estimating the blocking temperature of interacting core/shell nanoparticles is presented, which allows to be calculated more correctly than using the Neel relation. It was shown that together with an increase in the intensity of the magnetostatic interaction (concentration of nanoparticles) the blocking temperature increases, while the growth of the external magnetic field leads to the opposite effect. Moreover, the of large nanoparticles changes more significantly. A comparison of different methods for determining the blocking temperature from the ZFC and FC curves showed that the method for determining using the temperature derivative of the difference between ZFC and FC is more preferable.
- arXiv:2003.05618 [pdf, other]
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Title: Motility-induced buckling and glassy dynamics regulate three-dimensional transitions of bacterial monolayersComments: See Supplementary Information in Ancillary filesSubjects: Soft Condensed Matter (cond-mat.soft); Biological Physics (physics.bio-ph); Cell Behavior (q-bio.CB)
Many mature bacterial colonies and biofilms are complex three-dimensional (3D) structures. One key step in their developmental program is a transition from a two-dimensional (2D) monolayer into a 3D architecture. Despite the importance of controlling the growth of microbial colonies and biofilms in a variety of medical and industrial settings, the underlying physical mechanisms behind single-cell dynamics, collective behaviors of densely-packed cells, and 3D complex colony expansion remain largely unknown. In this work, we explore the mechanisms behind the 2D-to-3D transition of motile Pseudomonas aeruginosa colonies; we provide a new motility-induced, rate-dependent buckling mechanism for their out-of-plane growth. We find that swarming of motile bacterial colonies generate sustained in-plane flows. We show that the viscous shear stresses and dynamic pressures arising from these flows allow cells to overcome cell-substrate adhesion, leading to buckling of bacterial monolayers and growth into the third dimension. Modeling bacterial monolayers as 2D fluid films, we identify universal relationships that elucidate the competition between in-plane viscous stresses, pressure and cell-substrate adhesion. Furthermore, we show that bacterial monolayers can exhibit crossover from swarming to kinetically-arrested, glassy-like states above an onset density, resulting in distinct 2D-to-3D transition mechanisms. Combining experimental observations of P. aeruginosa colonies at single-cell resolution, molecular dynamics simulations of active systems, and theories of glassy dynamics and 2D fluid films, we develop a dynamical state diagram that predicts the state of the colony, and the mechanisms governing their 2D-to-3D transitions.
- arXiv:2003.05638 [pdf, other]
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Title: Floquet and Anomalous Floquet Weyl SemimetalsSubjects: Strongly Correlated Electrons (cond-mat.str-el); Atomic Physics (physics.atom-ph)
The periodic driving of a quantum system can enable new topological phases without analogs in static systems. This provides a route towards preparing non-equilibrium quantum phases rooted into the non-equilibrium nature by periodic driving engineering. Motivated by the ongoing considerable interest in topological semimetals, we are interested in the novel topological phases in the periodically driven topological semimetals without a static counterpart. We propose to design non-equilibrium topological semimetals in the regime of weakly driving field where the spectrum width of shares the same magnitude with the driving frequency. We identify two novel types of non-equilibrium Weyl semimetals (i.e., Floquet and anomalous Floquet Weyl semimetals) that do not exhibit analogues in equilibrium. The proposed setup is shown to be experimentally feasible using the state-of-the-art techniques used to control ultracold atoms in optical lattices.
- arXiv:2003.05645 [pdf, other]
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Title: Topological phase transition to Abelian anyon phases due to off-diagonal exchange interaction in the Kitaev spin liquid stateComments: 8 pages, 7 figuresSubjects: Strongly Correlated Electrons (cond-mat.str-el)
We investigate how the Kitaev spin liquid state described by Majorana fermions coupled with $Z_2$ gauge fields is affected by non-Kitaev interactions which exist in real candidate materials of the Kitaev magnet. It is found that the off-diagonal exchange interaction referred to as the $\Gamma'$ term dramatically changes the Majorana band structure in the case of the antiferromagnetic Kitaev interaction, and gives rise to a topological phase transition from a non-Abelian topological phase with the Chern number equal to $\pm 1$ to an Abelian phase with the Chern number equal to $\pm 2$, in which the $Z_{2}$ vortices behave as Abelian anyons. On the other hand, other non-Kitaev interactions such as the Heisenberg interaction and the $\Gamma$ term, only affect the bandwidth of the Majorana band as long as the spin liquid state is not destabilized.
- arXiv:2003.05648 [pdf, other]
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Title: Quantum phase-locking and frequency down-conversion in a driven cavity-qubit systemComments: 15 pages, 6 figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Optics (physics.optics)
We study a periodically driven qubit coupled to a quantized cavity mode. Despite its apparent simplicity, this system supports a rich variety of exotic phenomena, such as topological frequency conversion as recently discovered in [PRX 7, 041008 (2017)]. Here we report on a qualitatively different phenomenon that occurs in this platform, namely the phase-locking of the cavity mode to a rational fraction $r/q$ of the driving frequency $\Omega$. The phase-locking regime is characterized by the emergence of $q$-tuplets of stationary (Floquet) states whose quasienergies are separated by $\Omega/q$, up to exponentially small corrections. The Wigner functions of these states are nearly identical, and exhibit highly-regular and symmetric structure in phase space. Similarly to Floquet time crystals, these phase-locked states underlie discrete time-translation symmetry breaking in the model. We develop two complementary approaches for analyzing and predicting phase locking in the model, and use them to identify the conditions under which it occurs.
- arXiv:2003.05650 [pdf, ps, other]
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Title: MagGene: A genetic evolution program for magnetic structure predictionSubjects: Materials Science (cond-mat.mtrl-sci)
We have developed a software MagGene to predict magnetic structures by using genetic algorithm. Starting from an atom structure, MagGene repeatedly generates new magnetic structures and calls first-principles calculation engine to get the most stable structure. This software is applicable to both collinear and noncollinear systems. It is particularly convenient for predicting the magnetic structures of atomic systems with strong spin-orbit couplings and/or strong spin frustrations.
- arXiv:2003.05652 [pdf, ps, other]
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Title: Casimir effect in a dilute Bose gas in canonical ensemble within improved Hartree-Fock approximationAuthors: Nguyen Van ThuSubjects: Quantum Gases (cond-mat.quant-gas)
The Casimir effect in a dilute Bose gas confined between two planar walls is investigated in the canonical ensemble at zero temperature by means of Cornwall-Jackiw-Tomboulis effective action approach within the improved Hartree-Fock approximation. Our results show that: (i) the Casimir energy and the resulting Casimir force in the canonical ensemble remarkably differ from those in the grand canonical ensemble; (ii) when the distance between two planar walls increases, the Casimir energy and Casimir force decay in accordance with a half-integer power law in the canonical ensemble instead of an integer power law in the grand canonical ensemble.
- arXiv:2003.05655 [pdf, other]
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Title: Response to comment on "Quantum time crystals and interacting gauge theories in atomic Bose-Einstein condensates" by Syrwid, Kosior, and SachaSubjects: Quantum Gases (cond-mat.quant-gas)
In a recent comment [1] on our paper [2] Syrwid, Kosior, and Sacha (SKS) asserted that we did not correctly calculate the chiral soliton energy ${\cal E}_{LAB}$ in the lab frame, and further that the system we proposed is not capable of supporting a genuine quantum time crystal. We concede that we did not correctly calculate ${\cal E}_{LAB}$ but we illustrate below that our system can nonetheless display time crystal behavior with a ground state that is spatially localized and rotating.
- arXiv:2003.05680 [pdf, other]
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Title: Thermoelectric Penta-Silicene with a High Room-Temperature Figure of MeritComments: 17 pages, 5 figures, and 3 tablesSubjects: Materials Science (cond-mat.mtrl-sci); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Computational Physics (physics.comp-ph)
Silicon is one of the most frequently used chemical elements of the periodic table in nanotechnology. Two-dimensional (2D) silicene, a silicon analog of graphene, has been readily obtained to make field-effect transistors since 2015. Recently, as new members of the silicene family, penta-silicene and its nanoribbon have been experimentally grown on Ag(110) surface with exotic electronic properties. However, the thermoelectric performance of penta-silicene has not been so far studied that would hinder its potential applications of electric generation from waste heat and solid-state Peltier coolers. Based on the Boltzmann transport theory and ab initio calculations, we find that penta-silicene shows a remarkable room temperature figure of merit ZT of 3.4 and 3.0 at the reachable hole and electron concentrations, respectively. We attribute this high ZT to the superior pudding-mold electronic band structure and ultralow lattice thermal conductivity. The discovery provides new insight into the transport property of pentagonal nanostructures and highlights the potential applications of thermoelectric materials at room temperature.
- arXiv:2003.05696 [pdf]
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Title: Electronic states in a superlattice consisting of alternating strips of single-layer and bilayer grapheneSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
A model of a superlattice consisting of alternating strips of single-layer and bilayer graphene is proposed, whose parameters of the energy spectrum can be controlled by changing the external electric field perpendicular to the surface of the sample. Using the Kronig-Penney model, the dispersion equation is obtained, based on the analysis of which the energy spectrum of a graphene superlattice is studied depending on the ratio of the strip widths of single-layer and bilayer graphene. The results of the analytical solution are compared with the results of modeling by methods of the theory of the density functional. It is shown that the low-energy approximation used to derive the dispersion equation is valid when considering a superlattice with narrow strips of bilayer graphene and wide strips of single-layer graphene.
- arXiv:2003.05705 [pdf]
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Title: Genesis of primitive Hawaiian rejuvenated-stage lavas: Evidence for carbonatite metasomatism and implications for ancient eclogite sourceAuthors: Anastassia Y. BorisovaComments: 58 pages, 8 figures, 2 tablesSubjects: Geophysics (physics.geo-ph); Materials Science (cond-mat.mtrl-sci)
To constrain a contribution of deep carbonated mantle, to fractionation of Hf relative to rare earth elements (REE) in volcanic series, we examine available high-quality data on major, trace element and Nd-Hf isotope compositions of primitive lavas and glasses erupted during preshield, postshield and mostly rejuvenated stage of the Hawaiian hot spot (Pacific Ocean). Strong variations of Hf/Sm, Zr/Sm, Ti/Eu, K/Th, Nb/Th, La/K and Ba/K in the lavas are not features of the melt equilibration with residual amphibole or phlogopite, and cannot be due to variable degrees of batch or dynamic melting of uncarbonated lherzolite source. Enrichment in REE, Th and Ba relative to K, Hf, Zr, Ti and Nb together and low Si, high Na, K and Ca contents in the Hawaiian lavas are compositional features of carbonated mantle lithospheric to asthenospheric peridotite source affected by carbonatite metasomatism. In contrast, major and trace element signatures of most primitive preshield- and postshield-stage magmas require pyroxenite source.
The available data infer that Salt Lake Crater garnet pyroxenite xenoliths hosted by the Koolau volcano lavas on Oahu, Hawaii, were derived from deep eclogite source likely generating the carbonatite melts within the Hawaiian plume. Highly radiogenic Hf and decoupled Nd-Hf isotope systematics recorded in the Salt Lake Crater mantle xenolith series on Oahu may be explained by strong Hf fractionation relative to REE owing to ancient event of carbonatite metasomatism, which is likely related to partial melting of the deeply subducted carbonated eclogite within the Hawaiian plume. - arXiv:2003.05713 [pdf, ps, other]
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Title: Valence effect on the thermopower of Eu systemsComments: 7 pages, 3 figuresSubjects: Strongly Correlated Electrons (cond-mat.str-el)
We investigated the thermoelectric transport properties of EuNi2P2 and EuIr2Si2 in order to evaluate the relevance of Kondo interaction and valence fluctuations in these materials. While the thermal conductivities behave conventionally, the thermopower curves exhibit large values with pronounced maxima as typically observed in Ce- and Yb-based heavy-fermion materials. However, neither the positions of these maxima nor the absolute thermopower values at low temperature are in line with the heavy-fermion scenario and the moderately enhanced effective charge carrier masses. Instead, we may relate the thermopower in our materials to the temperature-dependent Eu valence by taking into account changes in the chemical potential. Our analysis confirms that valence fluctuations play an important role in EuNi2P2 and EuIr2Si2.
- arXiv:2003.05723 [pdf, other]
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Title: Superconductor-Insulator Transition and the Crossover to Non Equilibrium in two-dimensional Indium - Indium-Oxide compositeComments: 5 pages, 6 figuresSubjects: Superconductivity (cond-mat.supr-con)
Magnetic-field tuned superconductor to insulator transition was observed in a novel hybrid system of granular superconducting indium, deposited on indium oxide thin film, which exhibits global superconductivity at low magnetic fields. We have used annealing to tune the coupling to lie just at the borderline where superconductivity in the underlying InOx is suppressed, which is also close to the metal-insulator transition of the InOx. The hybrid system exhibits a "giant" magnetoresistance above the H-SIT, with critical behavior that manifests the duality between Cooper pairs and vortices.
- arXiv:2003.05732 [pdf, other]
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Title: Band Engineering of Dirac cones in Iron ChalcogenidesSubjects: Materials Science (cond-mat.mtrl-sci)
By band engineering the iron chalcogenide Fe(Se,Te) via ab-initio calculations, we search for topological surface states and realizations of Majorana bound states. Proposed topological states are expected to occur for non-stoichiometric compositions on a surface Dirac cone where issues like disorder scattering and charge transfer between relevant electronic states have to be addressed. However, this surface Dirac cone is well above the Fermi-level. Our goal is to theoretically design a substituted crystal in which the surface Dirac cone is shifted towards the Fermi-level by modifying the bulk material without disturbing the surface. Going beyond conventional density functional theory (DFT), we apply the coherent potential approximation (BEB-CPA) in a mixed basis pseudo-potential framework to scan the substitutional phase-space of co-substitutions on the Se-sites. We have identified iodine as a promising candidate for intrinsic doping. Our specific proposal is that FeSe$_{0.325}$I$_{0.175}$Te$_{0.5}$ is a very likely candidate to exhibit a Dirac cone right at the Fermi energy without inducing strong disorder scattering.
- arXiv:2003.05741 [pdf]
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Title: Spherical probes for simultaneous measurement of rotational and translational diffusion in 3 dimensionsSubjects: Applied Physics (physics.app-ph); Soft Condensed Matter (cond-mat.soft)
Real time visualization and tracking of colloidal particles with 3D resolution is essential for probing the local structure and dynamics in complex fluids. Although tracking translational motion of spherical colloids is well-known, accessing rotational dynamics of such particles remains a great challenge. Here, we report a novel approach of using fluorescently labeled raspberry-like colloids with an optical anisotropy to concurrently track translational and rotational dynamics in 3 dimensions. The raspberry-like particles are coated by a silica layer of adjustable thickness, which allows tuning the surface roughness. The synthesis and applicability of the proposed method is demonstrated by two types of probes: rough and smoothened. The accuracy of measuring Mean Squared (Angular) Displacements are also demonstrated by using these 2 probes dispersed in 2 different solvents. The presented 3D trackable colloids offer a high potential for wide range of applications and studies, such as probing crystallization dynamics, phase transitions and the effect of surface roughness on diffusion.
- arXiv:2003.05754 [pdf]
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Title: Unravelling Single Atom Electrocatalytic Activity of Transition Metal Doped PhosphoreneSubjects: Materials Science (cond-mat.mtrl-sci)
Developing single atom catalysts (SACs) for chemical reactions of vital importance in renewable energy sector has emerged as a need of the hour. In this perspective, transition metal based SACs with monolayer phosphorous (phosphorene) as the supporting material are scrutinized for their electrocatalytic activity towards oxygen reduction reaction (ORR), oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) from first principle calculations. The detailed screening study has confirmed a breaking of scaling relationship between ORR/OER intermediates resulting in varied activity trends across the transition metal series. Group 9 and 10 transition metal based SACs are identified as potential catalyst candidates with platinum single atom offering bifunctional activity for OER and HER with diminished overpotentials. Ambient condition stability analysis of SACs confirmed a different extent of interaction towards oxygen and water compared to pristine phosphorene suggesting room for improving the stability of phosphorene via chemical functionalization.
- arXiv:2003.05803 [pdf, other]
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Title: Collective Excitations of a One-Dimensional Quantum DropletComments: 5 pages, 1 figureJournal-ref: Phys. Rev. A 101, 051601(R) (2020)Subjects: Quantum Gases (cond-mat.quant-gas)
We calculate the excitation spectrum of a one-dimensional self-bound quantum droplet in a two-component bosonic mixture described by the Gross-Pitaevskii equation (GPE) with cubic and quadratic nonlinearities. The cubic term originates from the mean-field energy of the mixture proportional to the effective coupling constant $\delta g$, whereas the quadratic nonlinearity corresponds to the attractive beyond-mean-field contribution. The droplet properties are governed by a control parameter $\gamma\propto \delta g N^{2/3}$, where $N$ is the particle number. For large $\gamma>0$ the droplet features the flat-top shape with the discrete part of its spectrum consisting of plane-wave Bogoliubov phonons propagating through the flat-density bulk and reflected by edges of the droplet. With decreasing $\gamma$ these modes cross into the continuum, sequentially crossing the particle-emission threshold at specific critical values. A notable exception is the breathing mode which we find to be always bound. The balance point $\gamma = 0$ provides implementation of a system governed by the GPE with an unusual quadratic nonlinearity. This case is characterized by the ratio of the breathing-mode frequency to the particle-emission threshold equal to 0.8904. As $\gamma$ tends to $-\infty$ this ratio tends to 1 and the droplet transforms into the soliton solution of the integrable cubic GPE.
- arXiv:2003.05804 [pdf, other]
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Title: The Ising model in a light-induced quantized transverse fieldComments: 17 pages, 6 figuresJournal-ref: Phys. Rev. Research 2, 023131 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el)
We investigate the influence of light-matter interactions on correlated quantum matter by studying the paradigmatic Ising model subject to a quantum Rabi coupling. This type of coupling to a confined, spatially delocalized bosonic light mode, such as provided by an optical resonator, resembles a quantized transverse magnetic field of tunable strength. As a consequence, the symmetry-broken magnetic state breaks down for strong enough light-mater interactions to a paramagnetic state. The non-local character of the bosonic mode can change the quantum phase transition in a drastic manner, which we analyze quantitatively for the simplest case of a chain geometry (Dicke-Ising chain). The results show a direct transition between a magnetically ordered phase with zero photon density and a magnetically polarized phase with lasing behaviour of the light. Our predictions are equally valid for the dual quantized Ising chain in a conventional transverse magnetic field.
- arXiv:2003.05805 [pdf, other]
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Title: First Time Study of Magnetism and Ion Diffusion in Honeycomb Layered Oxide K$_2$Ni$_2$TeO$_6$ by Muon Spin RotationAuthors: N. Matsubara, E. Nocerino, O. K. Forslund, A. Zubayer, P. Gratrex, D. Andreica, J. Sugiyama, Z. Guguchia, S. Cottrell, A. Kalaboukhov, Y. Sassa, T. Masese, M. MånssonComments: 8 pages, 9 figuresSubjects: Materials Science (cond-mat.mtrl-sci)
Investigation of potassium-ion (K$^+$) dynamics in materials using magneto-spin properties is an indomitable feat, due to its inherently weak nuclear magnetic moment relative to other lithophile ions such as sodium. On the other hand, spin-polarised muons in muon spin rotation and relaxation ($\mu^+$SR) measurements are known to have strong gyromagnetic moment ideal for probing dynamics of ions with weak magneto-spin moments in materials. Here we report the magnetic properties and K$^+$ dynamics in honeycomb layered oxide material using $\mu^+$SR measurements. K$_2$Ni$_2$TeO$_6$ exhibits an antiferromagnetic transition at 26 K, as further affirmed by magnetic susceptibility measurements. Moreover, K$_2$Ni$_2$TeO$_6$ becomes antiferromagnetic under a first-order phase transition, with a possible commensurate spin ordering. $\mu^+$SR studies performed on K$_2$Ni$_2$TeO$_6$ at high temperatures reveal potassium ions (K$^+$) to be mobile beyond 250 K (with an extrapolated activation energy of 120 (13) meV), revealing for the first time that K$^+$ dynamics in potassium-based materials can be measured using $\mu^+$SR.
- arXiv:2003.05812 [pdf, other]
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Title: A mechanistic model for the growth of cylindrical debris particles in the presence of adhesionSubjects: Soft Condensed Matter (cond-mat.soft)
The wear volume is known to keep increasing during frictional processes, and Archard notably proposed a model to describe the probability of wear particle formation upon asperity collision in a two-body contact configuration. While this model is largely adopted in the investigations of wear, the presence of wear debris trapped between the surfaces changes the system into a three-body contact configuration already since the early stages of the process. In such a configuration, a significant amount of wear is produced at the interface between the trapped debris and the sliding bodies. Here, relying on analytical models, we develop a framework that describes crack growth in a three-body configuration at the particle-surface interface. We then show that crack growth is favoured within the sliding surfaces, instead of within the debris particle, and test such result by means of numerical simulations with a phase-field approach to fracture. This leads to an increase in the wear volume and to debris particle accretion, rather than its break down. The effects of adhesion, coefficient of friction, and ratio of the applied global tangential and normal forces are also investigated.
- arXiv:2003.05815 [pdf, other]
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Title: Energy partition for anharmonic, undamped, classical oscillatorsComments: 5 pages, 3 figuresJournal-ref: J. Phys. A: Math. Theor. 53, 195001 (2020)Subjects: Statistical Mechanics (cond-mat.stat-mech); Classical Physics (physics.class-ph)
Using stochastic methods, general formulas for average kinetic and potential energies for anharmonic, undamped (frictionless), classical oscillators are derived. It is demonstrated that for potentials of $|x|^\nu$ ($\nu>0$) type energies are equipartitioned for the harmonic potential only. For potential wells weaker than parabolic potential energy dominates, while for potentials stronger than parabolic kinetic energy prevails. Due to energy conservation, the variances of kinetic and potential energies are equal. In the limiting case of the infinite rectangular potential well ($\nu\to\infty$) the whole energy is stored in the form of the kinetic energy and variances of energy distributions vanish.
- arXiv:2003.05824 [pdf, other]
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Title: Hybrid Particle-Field Molecular Dynamics Under Constant PressureAuthors: Sigbjørn Løland Bore, Hima Bindu Kolli, Antonio De Nicola, Maksym Byshkin, Toshihiro Kawakatsu, Giuseppe Milano, Michele CascellaComments: 24 pages, 7 figuresJournal-ref: J. Chem. Phys. 152, 184908 (2020)Subjects: Soft Condensed Matter (cond-mat.soft)
Hybrid particle-field methods are computationally efficient approaches for modelling soft matter systems. So far applications of these methodologies have been limited to constant volume conditions. Here, we reformulate particle-field interactions to represent systems coupled to constant external pressure. First, we show that the commonly used particle-field energy functional can be modified to model and parameterize the isotropic contributions to the pressure tensor without interfering with the microscopic forces on the particles. Second, we employ a square gradient particle-field interaction term to model non-isotropic contributions to the pressure tensor, such as in surface tension phenomena. This formulation is implemented within the hybrid particle-field molecular dynamics approach and is tested on a series of model systems. Simulations of a homogeneous water box demonstrate that it is possible to parameterize the equation of state to reproduce any target density for a given external pressure. Moreover, the same parameterization is transferable to systems of similar coarse-grained mapping resolution. Finally, we evaluate the feasibility of the proposed approach on coarse-grained models of phospholipids, finding that the term between water and the lipid hydrocarbon tails is alone sufficient to reproduce the experimental area per lipid in constant-pressure simulations, and to produce a qualitatively correct lateral pressure profile.
- arXiv:2003.05832 [pdf]
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Title: Towards smooth (010) beta-Ga2O3 films homoepitaxially grown by plasma assisted molecular beam epitaxy: The impact of substrate offcut and metal-to-oxygen flux ratioJournal-ref: Journal of Physics D: Applied Physics (2020)Subjects: Materials Science (cond-mat.mtrl-sci)
Smooth interfaces and surfaces are beneficial for most (opto)electronic devices based on thin films and their heterostructures. For example, smoother interfaces in (010) beta-Ga2O3/(AlxGa1-x)2O3 heterostructures, whose roughness is ruled by that of the Ga2O3 layer, can enable higher mobility 2DEGs by reducing interface roughness scattering. To this end we experimentally prove that a substrate offcut along the [001] direction allows to obtain smooth beta-Ga2O3 layers in (010)-homoepitaxy under metal-rich conditions. Applying In-mediated metal-exchange catalysis (MEXCAT) in molecular beam epitaxy at high substrate temperatures (Tg = 900 {\deg}C) we compare the morphology of layers grown on (010)-oriented substrates with different unintentional offcuts. The layer roughness is generally ruled by (i) (110) and (-110)-facets visible as elongated features along the [001] direction (rms < 0.5 nm), and (ii) trenches (5-10 nm deep) orthogonal to [001]. We show that an unintentional substrate offcut of only 0.1{\deg} almost oriented along the [001] direction suppresses these trenches resulting in a smooth morphology with a roughness exclusively determined by the facets, i.e., rms 0.2 nm. Since we found the facet-and-trench morphology in layers grown by MBE with and without MEXCAT, we propose that the general growth mechanism for (010)-homoepitaxy is ruled by island growth whose coalescence results in the formation of the trenches. The presence of a substrate offcut in the [001] direction can allow for step-flow growth or island nucleation at the step edges, which prevents the formation of trenches. Moreover, we give experimental evidence for a decreasing surface diffusion length or increasing nucleation density with decreasing metal-to-oxygen flux ratio. Based on our results we can rule-out step bunching as cause of the trench formation as well as a surfactant-effect of indium during MEXCAT.
- arXiv:2003.05840 [pdf, other]
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Title: Designing Magnetic Topological van der Waals HeterostructureSubjects: Materials Science (cond-mat.mtrl-sci)
We demonstrate a new method of designing 2D functional magnetic topological heterostructure (HS) by exploiting the vdw heterostructure (vdw-HS) through combining 2D magnet CrI$_3$ and 2D materials (Ge/Sb) to realize new 2D topological system with nonzero Chern number (C=1) and chiral edge state. The nontrivial topology originates primarily from the CrI$_3$ layer while the non-magnetic element induces the charge transfer process and proximity enhanced spin-orbit coupling. Due to these unique properties, our topological magnetic vdw-HS overcomes the weak magnetization via proximity effect in previous designs since the magnetization and topology coexist in the same magnetic layer. Specifically, our systems of bilayer CrI$_3$/Sb and trilayer CrI$_3$/Sb/CrI$_3$ exhibit different topological ground state ranging from antiferromagnetic topological crystalline insulator (C$_M$= 2) to a QAHE. These nontrivial topological transition is shown to be switchable in a trilayer configuration due to the magnetic switching from antiferromagnetism to ferromangetism in the presence an external perpendicular electric field with value as small as 0.05 eV/A. Thus our study proposes a realistic system to design switchable magnetic topological device with electric field.
- arXiv:2003.05845 [pdf, ps, other]
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Title: Quantum control beyond the adiabatic regime in 2D curved matter-wave guidesSubjects: Quantum Physics (quant-ph); Quantum Gases (cond-mat.quant-gas)
The propagation of matter waves in curved geometry is relevant for electrons in nano-wires, solid-state physics structures and atomtronics. Curvature effects are usually addressed within the adiabatic limit and treated via an effective potential acting on the manifold to which the particles are strongly confined. However, the strength of the confinements that can be achieved experimentally are in practice limited, and the adiabatic approximation framework often appears too restrictive for the realistic design of relevant propagation structures. Here, we explore the design of 2D sharply bent wave-guides for the propagation of matter waves beyond the adiabatic regime. The bend design, which enables the connection of guide components rotated by an arbitrary angle and of arbitrary curvatures, rests on an exact inverse-engineering technique. The resolution of the full 2D Schr\"odinger equation in curved geometry shows that our method yields reflectionless guides with a transverse stability improved by several orders of magnitude when compared to circular guides of similar size.
- arXiv:2003.05850 [pdf, other]
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Title: Toward a room temperature Schafroth superconductor based on charged excitonic complexesAuthors: Z. Sun, J. Beaumariage, Q. Cao, K. Watanabe, T. Taniguchi, B. Hunt, I. V. Bondarev, D. W. SnokeSubjects: Superconductivity (cond-mat.supr-con)
In 1954, Schafroth proposed a mechanism for superconductivity that is physically possible, but ended up not being the explanation of the well known BCS superconductors. The proposal argued correctly that a Bose condensate of charged bosons should also be a superconductor. In 1996, V.I. Yudson proposed a way to produce a charged boson by attaching two free charges to an exciton in a semiconductor, to make a "quaternion". While that state was never seen in III-V semiconductors, our calculations show that it is predicted to be stable in structures made with monolayers of transition metal dichalcogenide (TMD) materials. We present experimental spectroscopic measurements that agree with this theory, which indicate that we have observed this charged-boson state in this type of structure. This opens up a new path for pursuing room temperature superconductivity.
- arXiv:2003.05868 [pdf, other]
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Title: Full Counting Statistics of the momentum occupation numbers of the Tonks-Girardeau gasComments: 10 pages, 4 figuresSubjects: Quantum Gases (cond-mat.quant-gas)
We compute the fluctuations of the number of bosons with a given momentum for the Tonks-Girardeau gas at zero temperature. We show that correlations between opposite momenta, which is an important fingerprint of long range order in weakly interacting Bose systems, are suppressed and that the full distribution of the number of bosons with non zero momentum is exponential. The distribution of the quasi-condensate is however quasi Gaussian. Experimental relevance of our findings for recent cold atoms experiments are discussed.
- arXiv:2003.05896 [pdf, other]
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Title: Connecting Inverse Design with Experimentally Relevant ModelsAuthors: Beth A LindquistComments: 9 pages, 3 figures, 33rd Annual CSP workshopSubjects: Soft Condensed Matter (cond-mat.soft)
While colloids are promising building blocks for the self-assembly of materials with novel microstructures, their numerous tunable parameters inhibit brute force searching for appropriate parameter combinations that yield self-assembly of a desired structure. Instead, inverse approaches that invoke a systematic optimization framework can effectively navigate this design space. In this proceeding, we apply one such inverse technique, Relative Entropy Minimization, to discover isotropic pairwise interaction potentials that prompt self-assembly of clusters in silico. The functional form of the pair interaction is chosen to model a mixture of charged colloids and neutral polymers that act as depletants, and the parameters are directly connected to experimentally tunable quantities.
- arXiv:2003.05904 [pdf, other]
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Title: Direct determination of the Tomonaga-Luttinger parameter $K$ in quasi-one-dimensional spin systemsComments: Main manuscript (5 pages, 4 figures) and Supplemental Material (3 pages, 2 figures), 8 pages, 6 figures in totalSubjects: Strongly Correlated Electrons (cond-mat.str-el)
We test the analytical formula for the enhancement of the nuclear magnetic resonance rate $T_1^{-1}$ by the critical spin fluctuations, over the simple power-law dependence predicted for purely one-dimensional spin system, recently derived in the random phase approximation [M. Dupont et al., Phys. Rev. B 98, 094403 (2018)]. This new prediction is experimentally confirmed by excellent fits to the published temperature dependence of $T_1^{-1}$ data in the two representative spin compounds, (C$_7$H$_{10}$N)$_2$CuBr$_4$ (DIMPY) and BaCo$_2$V$_2$O$_8$, providing at the same time a direct and convenient experimental determination of the Tomonaga-Luttinger-liquid parameter $K$, very well in agreement with theoretical predictions.
- arXiv:2003.05909 [pdf, other]
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Title: Extent of Fermi-surface reconstruction in the high-temperature superconductor HgBa$_2$CuO$_{4+δ}$Authors: Mun K. Chan, Ross D. McDonald, Brad J. Ramshaw, Jon B. Betts, Arkady Shekhter, Eric D. Bauer, Neil HarrisonComments: 5 pages. 3 FiguresJournal-ref: PNAS, www.pnas.org/cgi/doi/10.1073/pnas.1914166117 (2020)Subjects: Superconductivity (cond-mat.supr-con); Strongly Correlated Electrons (cond-mat.str-el)
High magnetic fields have revealed a surprisingly small Fermi-surface in underdoped cuprates, possibly resulting from Fermi-surface reconstruction due to an order parameter that breaks translational symmetry of the crystal lattice. A crucial issue concerns the doping extent of this state and its relationship to the principal pseudogap and superconducting phases. We employ pulsed magnetic field measurements on the cuprate HgBa$_2$CuO$_{4+\delta}$ to identify signatures of Fermi surface reconstruction from a sign change of the Hall effect and a peak in the temperature-dependent planar resistivity. We trace the termination of Fermi-surface reconstruction to two hole concentrations where the superconducting upper critical fields are found to be enhanced. One of these points is associated with the pseudogap end-point near optimal doping. These results connect the Fermi-surface reconstruction to both superconductivity and the pseudogap phenomena.
- arXiv:2003.05914 [pdf, other]
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Title: Path integral contour deformations for noisy observablesComments: 7 pages, 2 figuresSubjects: High Energy Physics - Lattice (hep-lat); Strongly Correlated Electrons (cond-mat.str-el); High Energy Physics - Phenomenology (hep-ph); High Energy Physics - Theory (hep-th)
Monte Carlo studies of many quantum systems face exponentially severe signal-to-noise problems. We show that noise arising from complex phase fluctuations of observables can be reduced without introducing bias using path integral contour deformation techniques. A numerical study of contour deformations for correlation functions in Abelian gauge theory and complex scalar field theory demonstrates that variance can be reduced by orders of magnitude without modifying Monte Carlo sampling.
- arXiv:2003.05918 [pdf, other]
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Title: Nonlinear friction in underdamped anharmonic stochastic oscillatorsComments: 10 pagesSubjects: Statistical Mechanics (cond-mat.stat-mech)
Stationary states of overdamped anharmonic stochastic oscillators driven by L\'evy noise are typically multimodal. The very same situation is recorded for an underdamped L\'evy noise driven motion in single-well potentials with linear friction. Within current manuscript we relax the assumption that the friction experienced by a particle is linear. Using computer simulations, we study underdamped motion in single-well potentials in the regime of nonlinear friction. We demonstrate that it is relatively easy to observe multimodality in the velocity distribution as it is determined by the friction itself and it is the same as the multimodality in the overdamped case with the analogous deterministic force. Contrary to the velocity marginal density, it is more difficult to produce multimodality in the position. Nevertheless, for fine-tuned nonlinear friction, the spatial multimodality can be recorded.
- arXiv:2003.05919 [pdf, other]
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Title: Damping of elementary excitations in one-dimensional dipolar Bose gasesComments: 6 pages, 3 figuresSubjects: Quantum Gases (cond-mat.quant-gas); Atomic Physics (physics.atom-ph)
In the presence of dipolar interactions the excitation spectrum of a Bose gas can acquire a local minimum. The corresponding quasiparticles are known as rotons. They are gaped and do not decay at zero temperature. Here we study the decay of rotons in one-dimensional Bose gases at low temperatures. It predominantly occurs due to the backscattering of thermal phonons on rotons. The resulting rate scales with the third power of temperature and is inversely proportional to the sixth power of the roton gap near the solidification phase transition. The hydrodynamic approach used here enables us to find the decay rate for quasiparticles at practically any momenta, with minimal assumptions on the exact form of the interparticle interactions. Our results are an essential prerequisite for the description of all the dissipative phenomena in dipolar gases and have direct experimental relevance.
- arXiv:2003.05923 [pdf]
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Title: Efficient spin torques in antiferromagnetic CoO/Pt quantified by comparing field- and current- induced switchingAuthors: Lorenzo Baldrati, Christin Schmitt, Olena Gomonay, Romain Lebrun, Rafael Ramos, Eiji Saitoh, Jairo Sinova, Mathias KläuiComments: 14 pages, 3 figuresSubjects: Materials Science (cond-mat.mtrl-sci)
We achieve current-induced switching in collinear insulating antiferromagnetic CoO/Pt, with fourfold in-plane magnetic anisotropy, measured electrically by spin Hall magnetoresistance. We exploit the reversible spin flop transition in the CoO film, controlled by a magnetic field, to unambiguously evidence the current-induced antiferromagnetic switching. By applying current pulses and magnetic fields of different magnitude and orientation, we quantify directly the efficiency and direction of the acting current-induced torques and estimate a current-field equivalence ratio of $4x10^{-11} T A^{-1} m^2$.
- arXiv:2003.05925 [pdf, other]
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Title: Realising a species-selective double well with multiple-radiofrequency-dressed potentialsComments: 11 pages, 4 figuresSubjects: Quantum Gases (cond-mat.quant-gas); Atomic Physics (physics.atom-ph)
Techniques to manipulate the individual constituents of an ultracold mixture are key to investigating impurity physics. In this work, we confine a mixture of the hyperfine ground states of Rb-87 in a double-well potential. The potential is produced by dressing the atoms with multiple radiofrequencies. The amplitude and phase of each frequency component of the dressing field are individually controlled to independently manipulate each species. Furthermore, we verify that our mixture of hyperfine states is collisionally stable, with no observable inelastic loss.
- arXiv:2003.05933 [pdf, other]
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Title: Polarization as a tuning parameter for Floquet engineering: magnetism in the honeycomb, square, and triangular Mott insulatorsComments: 24 pages, 21 figuresSubjects: Strongly Correlated Electrons (cond-mat.str-el)
Magnetic exchange couplings can be tuned by coupling to periodic light, where the frequency and amplitude are typically varied: a process known as Floquet engineering. The polarization of the light is also important, and in this paper, we show how different polarizations, including several types of unpolarized light, can tune the exchange couplings in distinct ways. Using unpolarized light, for example, it is possible to tune the material without breaking either time-reversal or any lattice symmetries. To illustrate these effects generically, we consider single-band Hubbard models at half-filling on the honeycomb, square and triangular lattices. We derive the effective Heisenberg spin models to fourth order in perturbation theory for arbitrary fixed polarizations, and several types of unpolarized light that preserve time-reversal and lattice symmetries. Coupling these models to periodic light tunes first, second and third neighbor exchange couplings, as well as ring exchange terms on the square and triangular lattices. Circularly polarized light induces chiral fields for the honeycomb and triangular lattices, which favors non-coplanar magnetism and potential chiral spin liquids. We discuss how to maximize the enhancement of the couplings without inducing heating.
- arXiv:2003.05937 [pdf, other]
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Title: Suppressing dissipation in a Floquet-Hubbard systemAuthors: Konrad Viebahn, Joaquìn Minguzzi, Kilian Sandholzer, Anne-Sophie Walter, Frederik Görg, Tilman EsslingerComments: 9 pages, 4 figuresSubjects: Quantum Gases (cond-mat.quant-gas); Atomic Physics (physics.atom-ph)
The concept of `Floquet engineering' relies on an external periodic drive to realise novel, effectively static Hamiltonians. This technique is being explored in experimental platforms across physics, including ultracold atoms, laser-driven electron systems, nuclear magnetic resonance, and trapped ions. The key challenge in Floquet engineering is to avoid the uncontrolled absorption of photons from the drive, especially in interacting systems in which the excitation spectrum becomes effectively dense. The resulting dissipative coupling to higher-lying modes, such as the excited bands of an optical lattice, has been explored in recent experimental and theoretical works, but the demonstration of a broadly applicable method to mitigate this effect is lacking. Here, we show how two-path quantum interference, applied to strongly-correlated fermions in a driven optical lattice, suppresses dissipative coupling to higher bands and increases the lifetime of double occupancies and spin-correlations by two to three orders of magnitude. Interference is achieved by introducing a weak second modulation at twice the fundamental driving frequency with a definite relative phase. This technique is shown to suppress dissipation in both weakly and strongly interacting regimes of a driven Hubbard system, opening an avenue to realising low-temperature phases of matter in interacting Floquet systems.
Replacements
- arXiv:1702.04017 (replaced) [pdf, other]
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Title: Internal DLA on Sierpinski gasket graphsComments: 24 pages, 2 figures. Final version, to appear as Chapter 7 of "Analysis and Geometry on Graphs and Manifolds," M. Keller, D. Lenz, and R.K. Wojciechowski, Cambridge University Press (2020)Subjects: Probability (math.PR); Statistical Mechanics (cond-mat.stat-mech); Mathematical Physics (math-ph); Metric Geometry (math.MG)
Internal diffusion-limited aggregation (IDLA) is a stochastic growth model on a graph $G$ which describes the formation of a random set of vertices growing from the origin (some fixed vertex) of $G$. Particles start at the origin and perform simple random walks; each particle moves until it lands on a site which was not previously visited by other particles. This random set of occupied sites in $G$ is called the IDLA cluster.
In this paper we consider IDLA on Sierpinski gasket graphs, and show that the IDLA cluster fills balls (in the graph metric) with probability 1. - arXiv:1711.08428 (replaced) [pdf, other]
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Title: Computing return times or return periods with rare event algorithmsAuthors: Thibault Lestang, Francesco Ragone, Charles-Edouard Bréhier, Corentin Herbert, Freddy BouchetJournal-ref: J. Stat. Mech. (2018) 043213Subjects: Statistical Mechanics (cond-mat.stat-mech); Computational Physics (physics.comp-ph); Data Analysis, Statistics and Probability (physics.data-an)
The average time between two occurrences of the same event, referred to as its return time (or return period), is a useful statistical concept for practical applications. For instance insurances or public agency may be interested by the return time of a 10m flood of the Seine river in Paris. However, due to their scarcity, reliably estimating return times for rare events is very difficult using either observational data or direct numerical simulations. For rare events, an estimator for return times can be built from the extrema of the observable on trajectory blocks. Here, we show that this estimator can be improved to remain accurate for return times of the order of the block size. More importantly, we show that this approach can be generalised to estimate return times from numerical algorithms specifically designed to sample rare events. So far those algorithms often compute probabilities, rather than return times. The approach we propose provides a computationally extremely efficient way to estimate numerically the return times of rare events for a dynamical system, gaining several orders of magnitude of computational costs. We illustrate the method on two kinds of observables, instantaneous and time-averaged, using two different rare event algorithms, for a simple stochastic process, the Ornstein-Uhlenbeck process. As an example of realistic applications to complex systems, we finally discuss extreme values of the drag on an object in a turbulent flow.
- arXiv:1802.05553 (replaced) [pdf, ps, other]
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Title: Turbulence Excitation in Counter-Streaming Paraxial Superfluids of LightComments: Accepted for publication in Physical Review ASubjects: Quantum Physics (quant-ph); Quantum Gases (cond-mat.quant-gas); Optics (physics.optics); Plasma Physics (physics.plasm-ph)
Turbulence in the quantum (superfluid) regime, similarly to its classical counterpart, continues to attract a great deal of scientific inquiry, due to the yet high number of unresolved problems. While turbulent states can be routinely created in degenerate atomic gases, there is no generic scheme to produce turbulence in fluids of light. Under paraxial propagation, light in bulk nonlinear media behaves as a two-dimensional superfluid, described by a nonlinear Schr\"{o}dinger equation formally equivalent to the Gross-Pitaevskii model of a weakly interacting Bose gas, where photon-photon interactions are mediated by a third order (Kerr) nonlinearity. Here, we develop the theory describing the onset of a kinetic instability when two paraxial optical fluids with different streaming velocities interact via the optical nonlinearity. From numerical simulations of the nonlinear Schr\"{o}dinger equation, we further characterize the onset of the instability and describe its saturation in the form of vortex nucleation and excitation of turbulence. The experimental observation of such effects is also discussed. The class of instabilities described here thus provide a natural route towards the investigation of quantum (superfluid) turbulence, structure formation and out-of-equilibrium dynamics in superfluids of light.
- arXiv:1902.09550 (replaced) [pdf, other]
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Title: $\textit{Ab Initio}$ Mismatched Interface Theory of Graphene on $α$-RuCl$_3$: Doping and MagnetismJournal-ref: Phys. Rev. Lett. 124, 106804 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el)
Recent developments in twisted and lattice-mismatched bilayers have revealed a rich phase space of van der Waals systems and generated excitement. Among these systems are heterobilayers which can offer new opportunities to control van der Waals systems with strong in plane correlations such as spin-orbit-assisted Mott insulator $\alpha$-RuCl$_3$. Nevertheless, a theoretical $\textit{ab initio}$ framework for mismatched heterobilayers without even approximate periodicity is sorely lacking. We propose a general strategy for calculating electronic properties of such systems, mismatched interface theory (MINT), and apply it to the graphene/$\alpha$-RuCl$_{3}$ (GR/$\alpha$-RuCl$_{3}$) heterostructure. Using MINT, we predict uniform doping of 4.77$\%$ from graphene to $\alpha$-RuCl$_3$ and magnetic interactions in $\alpha$-RuCl$_3$ to shift the system toward the Kitaev point. Hence we demonstrate that MINT can guide targeted materialization of desired model systems and discuss recent experiments on GR/$\alpha$-RuCl$_{3}$ heterostructures.
- arXiv:1904.04266 (replaced) [pdf, other]
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Title: Ergodicity-breaking arising from Hilbert space fragmentation in dipole-conserving HamiltoniansComments: close to published version: 10 pages + Appendices. Updated discussions and contentJournal-ref: Phys. Rev. X 10, 011047 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el); Statistical Mechanics (cond-mat.stat-mech)
We show that the combination of charge and dipole conservation---characteristic of fracton systems---leads to an extensive fragmentation of the Hilbert space, which in turn can lead to a breakdown of thermalization. As a concrete example, we investigate the out-of-equilibrium dynamics of one-dimensional spin-1 models that conserve charge (total $S^z$) and its associated dipole moment. First, we consider a minimal model including only three-site terms and find that the infinite temperature auto-correlation saturates to a finite value---showcasing non-thermal behavior. The absence of thermalization is identified as a consequence of the strong fragmentation of the Hilbert space into exponentially many invariant subspaces in the local $S^z$ basis, arising from the interplay of dipole conservation and local interactions. Second, we extend the model by including four-site terms and find that this perturbation leads to a weak fragmentation: the system still has exponentially many invariant subspaces, but they are no longer sufficient to avoid thermalization for typical initial states. More generally, for any finite range of interactions, the system still exhibits non-thermal eigenstates appearing throughout the entire spectrum. We compare our results to charge and dipole moment conserving random unitary circuit models for which we reach identical conclusions.
- arXiv:1904.07657 (replaced) [pdf, other]
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Title: Level-set based design of Wang tiles for modelling complex microstructuresAuthors: Martin Doškář (1), Jan Zeman (1 and 2), Daniel Rypl (1), Jan Novák (1) ((1) Faculty of Civil Engineering, Czech Technical University in Prague, (2) Institute of Information Theory and Automation)Comments: 16 pages, 16 figures. Abstract has been shortened to match the arXiv.org's limit of 1920 charactersJournal-ref: Computer-Aided Design 123 (2020) 102827Subjects: Computational Geometry (cs.CG); Materials Science (cond-mat.mtrl-sci)
Microstructural geometry plays a critical role in the response of heterogeneous materials. Consequently, methods for generating microstructural samples are increasingly crucial to advanced numerical analyses. We extend Sonon et al.'s unified framework, developed originally for generating particulate and foam-like microstructural geometries of Periodic Unit Cells, to non-periodic microstructural representations based on the formalism of Wang tiles. This formalism has been recently proposed in order to generalize the Periodic Unit Cell approach, enabling a fast synthesis of arbitrarily large, stochastic microstructural samples from a handful of domains with predefined compatibility constraints. However, a robust procedure capable of designing complex, three-dimensional, foam-like and cellular morphologies of Wang tiles has not yet been proposed. This contribution fills the gap by significantly broadening the applicability of the tiling concept.
Since the original Sonon et al.'s framework builds on a random sequential addition of particles enhanced with an implicit representation of particle boundaries by the level-set field, we first devise an analysis based on a connectivity graph of a tile set, resolving the question where a particle should be copied when it intersects a tile boundary. Next, we introduce several modifications to the original algorithm that are necessary to ensure microstructural compatibility in the generalized periodicity setting of Wang tiles. Having established a universal procedure for generating tile morphologies, we compare strictly aperiodic and stochastic sets with the same cardinality in terms of reducing the artificial periodicity in reconstructed microstructural samples. We demonstrate the superiority of the vertex-defined tile sets for two-dimensional problems and illustrate the capabilities of the algorithm with two- and three-dimensional examples. - arXiv:1904.10330 (replaced) [pdf]
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Title: Modeling of Transient Trapping of Fatty Acid Tails in PhospholipidsComments: 33 pages, 5 figures, published in Soft MatterJournal-ref: Soft Matter, 16, 3245-3256 (2020)Subjects: Soft Condensed Matter (cond-mat.soft); Biological Physics (physics.bio-ph)
We present the derivation of a new model to describe neutron spin echo spectroscopy and quasi-elastic neutron scattering data on liposomes. We compare the new model with existing approaches and benchmark it with experimental data. The analysis indicates the importance of including all major contributions into modeling of the intermediate scattering function. Simultaneous analysis of the experimental data on lipids with full contrast and tail contrast matched samples, reveals highly confined lipid tail motion. A comparison of their dynamics demonstrates the statistical independ-ence of tail-motion and height-height correlation of the membrane. A more detailed analysis indi-cates that lipid tails are subject to relaxations in a potential with cylindrical symmetry, in addition to the undulation and diffusive motion of the liposome. Despite substantial differences in the chemis-try of the fatty acid tails, the observation indicates a universal behavior. The analysis of partially deuterated systems confirms the strong contribution of the lipid tail to the intermediate scattering function. Within the time range from 5 to 100 ns, the intermediate scattering function can be de-scribed by the height-height correlation function. The existence of the fast-localized tail motion and the contribution of slow translational diffusion of liposomes determines the intermediate scattering function for t < 5 ns and t > 100 ns, respectively. Taking into account the limited time window lowers the bending moduli by a factor of 1.3 (DOPC) to 2 (DMPC) compared to the full range.
- arXiv:1905.12523 (replaced) [pdf, other]
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Title: Coherent long-range transfer of angular momentum between magnon Kittel modes by phononsAuthors: Kyongmo An, Artem N. Litvinenko, Ryuhei Kohno, Aufa A. Fuad, Vladimir V. Naletov, Laurent Vila, Ursula Ebels, Grégoire de Loubens, Hervé Hurdequint, Nathan Beaulieu, Jamal Ben Youssef, Nicolas Vukadinovic, Gerrit E.W. Bauer, Andrei N. Slavin, Vasil S. Tiberkevich, Olivier KleinJournal-ref: Phys. Rev. B 101, 060407 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci)
We report ferromagnetic resonance in the normal configuration of an electrically insulating magnetic bilayer consisting of two yttrium iron garnet (YIG) films epitaxially grown on both sides of a 0.5-mm-thick nonmagnetic gadolinium gallium garnet (GGG) slab. An interference pattern is observed and it is explained as the strong coupling of the magnetization dynamics of the two YIG layers either in phase or out of phase by the standing transverse sound waves, which are excited through a magnetoelastic interaction. This coherent mediation of angular momentum by circularly polarized phonons through a nonmagnetic material over macroscopic distances can be useful for future information technologies.
- arXiv:1906.03261 (replaced) [pdf, other]
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Title: Harnessing elasticity to generate self-oscillation via an electrohydrodynamic instabilityJournal-ref: Journal of Fluid Mechanics, 888, A31 (2020)Subjects: Soft Condensed Matter (cond-mat.soft); Biological Physics (physics.bio-ph); Computational Physics (physics.comp-ph); Fluid Dynamics (physics.flu-dyn)
Under a steady DC electric field of sufficient strength, a weakly conducting dielectric sphere in a dielectric solvent with higher conductivity can undergo spontaneous spinning (Quincke rotation) through a pitchfork bifurcation. We design an object composed of a dielectric sphere and an elastic filament. By solving an elasto-electro-hydrodynamic (EEH) problem numerically, we uncover an EEH instability exhibiting diverse dynamic responses. Varying the bending stiffness of the filament, the composite object displays three behaviours: a stationary state, undulatory swimming and steady spinning, where the swimming results from a self-oscillatory instability through a Hopf bifurcation. By conducting a linear stability analysis incorporating an elastohydrodynamic model, we theoretically predict the growth rates and critical conditions, which agree well with the numerical counterparts. We also propose a reduced model system consisting of a minimal elastic structure which reproduces the EEH instability. The elasto-viscous response of the composite structure is able to transform the pitchfork bifurcation into a Hopf bifurcation, leading to self-oscillation. Our results imply a new way of harnessing elastic media to engineer self-oscillations, and more generally, to manipulate and diversify the bifurcations and the corresponding instabilities. These ideas will be useful in designing soft, environmentally adaptive machines.
- arXiv:1906.10448 (replaced) [pdf, other]
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Title: Unambiguous Electrical Detection of Spin-Charge Conversion in Lateral Spin-ValvesAuthors: Stuart A. Cavill, Chunli Huang, Manuel Offidani, Yu-Hsuan Lin, Miguel A. Cazalilla, Aires FerreiraComments: 6 pages, 2 figures + supplementary information (2 pages, 3 figures). Improved theory accounting for a much wider class of lateral spin-valve devices. Readability has been improved to make work accessible to wider audience. Title, abstract, main text, references and SM updated accordinglySubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Efficient detection of spin-charge conversion is crucial for advancing our understanding of emergent phenomena in spin-orbit-coupled nanostructures. Here, we provide proof of principle of an electrical detection scheme of spin-charge conversion that enables full disentanglement of competing spin-orbit coupling transport phenomena in diffusive lateral channels i.e. the inverse spin Hall effect (ISHE) and the spin galvanic effect (SGE). A suitable detection geometry in an applied oblique magnetic field is shown to provide direct access to spin-charge transport coefficients through a simple symmetry analysis of the output non-local resistance. The scheme is robust against tilting of the spin-injector magnetization, disorder and spurious non-spin related contributions to the non-local signal, and can be used to probe spin-charge conversion effects in both spin-valve and hybrid optospintronic devices.
- arXiv:1906.10632 (replaced) [pdf, other]
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Title: Unraveling the Mott-Peierls intrigue in Vanadium dioxideComments: 19 pages, 9 figuresJournal-ref: Phys. Rev. Research 2, 013298 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el)
Vanadium dioxide is one of the most studied strongly correlated materials. Nonetheless, the intertwining between electronic correlation and lattice effects has precluded a comprehensive description of the rutile metal to monoclinic insulator transition, in turn triggering a longstanding "the chicken or the egg" debate about which comes first, the Mott localisation or the Peierls distortion. Here, we suggest that this problem is in fact ill-posed: the electronic correlations and the lattice vibrations conspire to stabilise the monoclinic insulator, and so they must be both considered not to miss relevant pieces of the VO$_2$ physics. Specifically, we design a minimal model for VO$_2$ that includes all the important physical ingredients: the electronic correlations, the multi-orbital character, and the two components antiferrodistortive mode that condenses in the monoclinic insulator. We solve this model by dynamical mean-field theory within the adiabatic Born-Oppenheimer approximation. Consistently with the first-order character of the metal-insulator transition, the Born-Oppenheimer potential has a rich landscape, with minima corresponding to the undistorted phase and to the four equivalent distorted ones, and which translates into an equally rich thermodynamics that we uncover by the Monte Carlo method. Remarkably, we find that a distorted metal phase intrudes between the low-temperature distorted insulator and high-temperature undistorted metal, which sheds new light on the debated experimental evidence of a monoclinic metallic phase.
- arXiv:1906.10748 (replaced) [pdf, other]
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Title: Kondo Lattice Behavior Observed in the CeCu$_9$In$_2$ CompoundJournal-ref: Journal of Alloys and Compounds, Volume 803, September 2019, Pages 576-584Subjects: Strongly Correlated Electrons (cond-mat.str-el)
We report systematic studies of CeCu$_9$In$_2$, which appears to be a new Kondo lattice system. Electrical resistivity exhibits a logarithmic law characteristic of Kondo systems with a broad maximum at $T_{coh}\approx$45 K and it obeys the Fermi liquid theory at low temperature. Specific heat of CeCu$_9$In$_2$ is well described by the Einstein and Debye models with electronic part at high temperature. Fitting of the Schottky formula to low temperature 4f contribution to specific heat yielded crystal field splitting of 50.2 K between a doublet and quasi-quartet. The Schotte-Schotte model estimates roughly Kondo temperature as $T_K\approx$5 K, but does not reproduce well the data due to a sharp peak at 1.6 K. This structure should be attributed to a phase transition, a nature of which is possibly antiferromagnetic. Specific heat is characterized with increased Sommerfeld coefficient estimated as $\gamma\approx$132 mJ/(mole$\cdot$K$^2$). Spectra of the valence band, which have been collected with ultraviolet photoelectron spectroscopy (UPS), show a peak at binding energy$\approx$250 meV, which originates from the Ce 4f electrons and is related to the 4f$^1$$_{7/2}$ final state. Extracted 4f contribution to the spectral function exhibits also the enhancement of intensity in the vicinity of the Fermi level. Satellite structure of the Ce 3d levels spectra measured by X-ray photoelectron spectroscopy (XPS) has been analyzed within the framework of the Gunnarsson-Sch\"onhammer theory. Theoretical calculations based on density functional theory (FPLO method with LDA+U approach) delivered densities of states, band structures and Fermi surfaces for CeCu$_9$In$_2$ and LaCu$_9$In$_2$. The results indicate that Fermi surface nesting takes place in CeCu$_9$In$_2$.
- arXiv:1907.11226 (replaced) [pdf, other]
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Title: Multichannel interactions of two atoms in an optical tweezerAuthors: Jonathan D. Hood, Yichao Yu, Yen-Wei Lin, Jessie T. Zhang, Kenneth Wang, Lee R. Liu, Bo Gao, Kang-Kuen NiJournal-ref: Phys. Rev. Research 2, 023108 (2020)Subjects: Atomic Physics (physics.atom-ph); Quantum Gases (cond-mat.quant-gas); Quantum Physics (quant-ph)
The multichannel Na-Cs interactions are characterized by a series of measurements using two atoms in an optical tweezer, along with a multichannel quantum defect theory (MQDT). The triplet and singlet scattering lengths are measured by performing Raman spectroscopy of the Na-Cs motional states and least-bound molecular state in the tweezer. Magnetic Feshbach resonances are observed for only two atoms at fields which agree well with the MQDT. Our methodology, which promotes the idea of an effective theory of interaction, can be a key step towards the understanding and the description of more complex interactions. The tweezer-based measurements in particular will be an important tool for atom-molecule and molecule-molecule interactions, where high densities are experimentally challenging and where the interactions can be dominated by intra-species processes.
- arXiv:1907.11339 (replaced) [pdf, other]
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Title: Projected Proca Field Theory: a One-Loop StudyAuthors: R. F. Ozela, Van Sérgio Alves, E. C. Marino, Leandro O. Nascimento, J. F. Medeiros Neto, Rudnei O. Ramos, C. Morais SmithSubjects: High Energy Physics - Theory (hep-th); Superconductivity (cond-mat.supr-con); High Energy Physics - Phenomenology (hep-ph)
The recent discovery of two-dimensional Dirac materials, such as graphene and transition-metaldichalcogenides, has raised questions about the treatment of hybrid systems, in which electrons moving in a two-dimensional plane interact via virtual photons from the three-dimensional space. In this case, a projected non-local theory, known as Pseudo-QED, or reduced QED, has shown to provide a correct framework for describing the interactions displayed by these systems. In a related situation, in planar materials exhibiting a superconducting phase, the electromagnetic field has a typical exponential decay that is interpreted as the photons having an effective mass, as a consequence of the Anderson-Higgs mechanism. Here, we use an analogous projection to that used to obtain the pseudo-QED to derive a Pseudo-Proca equivalent model. In terms of this model, we unveil the main effects of attributing a mass to the photons and to the quasi-relativistic electrons. The one-loop radiative corrections to the electron mass, to the photon and to the electron-photon vertex are computed. We calculate the quantum corrections to the electron g-factor and show that it smoothly goes to zero in the limit when the photon mass is much larger than the electron mass. In addition, we correct the results obtained for graphene within Pseudo-QED in the limit when the photon mass vanishes.
- arXiv:1907.12115 (replaced) [pdf, other]
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Title: Universal spin dynamics in infinite-temperature one-dimensional quantum magnetsComments: 7 pages, 3 figures, supplemental material included (7 pages, 6 figures)Journal-ref: Phys. Rev. B 101, 121106 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el); Statistical Mechanics (cond-mat.stat-mech)
We address the nature of spin dynamics in various integrable and non-integrable, isotropic and anisotropic quantum spin-$S$ chains, beyond the paradigmatic $S=1/2$ Heisenberg model. In particular, we investigate the algebraic long-time decay $\propto t^{-1/z}$ of the spin-spin correlation function at infinite temperature, using state-of-the-art simulations based on tensor network methods. We identify three universal regimes for the spin transport, independent of the exact microscopic model: (i) superdiffusive with $z=3/2$, as in the Kardar-Parisi-Zhang universality class, when the model is integrable with extra symmetries such as spin isotropy that drive the Drude weight to zero, (ii) ballistic with $z=1$ when the model is integrable with a finite Drude weight, and (iii) diffusive with $z=2$ with easy-axis anisotropy or without integrability, at variance with previous observations.
- arXiv:1908.00551 (replaced) [pdf, other]
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Title: Topological vacuum structure of the Schwinger model with matrix product statesComments: 15 pages, 10 figuresJournal-ref: Phys. Rev. D 101, 054507 (2020)Subjects: High Energy Physics - Lattice (hep-lat); Strongly Correlated Electrons (cond-mat.str-el); High Energy Physics - Theory (hep-th); Quantum Physics (quant-ph)
We numerically study the single-flavor Schwinger model with a topological $\theta$-term, which is practically inaccessible by standard lattice Monte Carlo simulations due to the sign problem. By using numerical methods based on tensor networks, especially the one-dimensional matrix product states, we explore the non-trivial $\theta$-dependence of several lattice and continuum quantities in the Hamiltonian formulation. In particular, we compute the ground-state energy, the electric field, the chiral fermion condensate, and the topological vacuum susceptibility for positive, zero, and even negative fermion mass. In the chiral limit, we demonstrate that the continuum model becomes independent of the vacuum angle $\theta$, thus respecting CP invariance, while lattice artifacts still depend on $\theta$. We also confirm that negative masses can be mapped to positive masses by shifting $\theta\rightarrow \theta +\pi$ due to the axial anomaly in the continuum, while lattice artifacts non-trivially distort this mapping. This mass regime is particularly interesting for the (3+1)-dimensional QCD analog of the Schwinger model, the sign problem of which requires the development and testing of new numerical techniques beyond the conventional Monte Carlo approach.
- arXiv:1908.06142 (replaced) [pdf, other]
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Title: Double Quantum Magnetometry at Large Static Magnetic FieldsComments: 5 pages and 2 figures, plus Supplemental MaterialJournal-ref: Phys. Rev. B 101, 104411 (2020)Subjects: Quantum Physics (quant-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We present a protocol to achieve double quantum magnetometry at large static magnetic fields. This is a regime where sensitive sample parameters, such as the chemical shift, get enhanced facilitating their characterization. In particular, our method delivers two-tone stroboscopic radiation patterns with modulated Rabi frequencies to achieve larger spectral signals. Furthermore, it does not introduce inhomogeneous broadening in the sample spectrum preventing signal misinterpretation. Moreover, our protocol is designed to work under realistic conditions such as the presence of moderate microwave power and errors on the radiation fields. Albeit we particularise to nitrogen vacancy centers, our protocol is general, thus applicable to distinct quantum sensors.
- arXiv:1908.07881 (replaced) [pdf]
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Title: Apollonian Packing in Polydisperse EmulsionsComments: 5 pages, 4 figuresJournal-ref: Soft Matter, 2020,16, 2426-2430Subjects: Soft Condensed Matter (cond-mat.soft); Materials Science (cond-mat.mtrl-sci); Chemical Physics (physics.chem-ph)
We have discovered the existence of polydisperse High Internal-Phase-Ratio Emulsions (HIPE) in which the internal-phase droplets, present at 95% volume fraction, remain spherical and organize themselves in the available space according to Apollonian packing rules. These polydisperse HIPE are formed during emulsification of surfactant-poor compositions of oil-surfactant-water two-phase systems. Their droplet size-distributions evolve spontaneously towards power laws with the Apollonian exponent. Small-Angle X-Ray Scattering performed on aged HIPEs demonstrated that the droplet packing structure coincided with that of a numerically simulated Random Apollonian Packing. We argue that these peculiar, space-filling assemblies are a result of coalescence and fragmentation processes obeying simple geometrical rules of conserving total volume and minimizing surface area.
- arXiv:1909.01594 (replaced) [pdf, other]
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Title: Bose-Einstein condensation of deconfined spinons in two dimensionsComments: Published in Phys. Rev. B March 11, 2020Journal-ref: Phys. Rev. B 101, 104412 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el)
The transition between the N\'{e}el antiferromagnet and the valence-bond solid state in two dimensions has become a paradigmatic example of deconfined quantum criticality, a non-Landau transition characterized by fractionalized excitations (spinons). We consider an extension of this scenario whereby the deconfined spinons are subject to a magnetic field. The primary purpose is to identify the exotic scenario of a Bose-Einstein condensate of spinons. We employ quantum Monte Carlo simulations of the \mbox{$J$-$Q$} model with a magnetic field and perform a quantum field theoretic analysis of the magnetic field and temperature dependence of thermodynamic quantities. The combined analysis provides compelling evidence for the Bose-Einstein condensation of spinons and also demonstrates an extended temperature regime in which the system is best described as a gas of spinons interacting with an emergent gauge field.
- arXiv:1909.03089 (replaced) [pdf, other]
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Title: Octupolar order in d-orbital Mott insulatorsComments: 7 pages, 4 figs, PRB published version. For parallel experimental work see arXiv:1909.03113Journal-ref: Phys. Rev. B 101, 054439 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el)
Motivated by experimental and theoretical interest in realizing multipolar orders in $d$-orbital materials, we discuss the quantum magnetism of $J\!=\!2$ ions which can be realized in spin-orbit coupled oxides with $5d^2$ transition metal ions. Based on the crystal field environment, we argue for a splitting of the $J\!=\!2$ multiplet, leading to a low lying non-Kramers doublet which hosts quadrupolar and octupolar moments. We discuss a microscopic mechanism whereby the combined perturbative effects of orbital repulsion and antiferromagnetic Heisenberg spin interactions leads to ferro-octupolar coupling between neighboring sites, and stabilizes ferro-octupolar order for a face-centered cubic lattice. This same mechanism is also shown to disfavor quadrupolar ordering. We show that studying crystal field levels via Raman scattering in a magnetic field provides a probe of octupolar order. We study spin dynamics in the ferro-octupolar state using a slave-boson approach, uncovering a gapped and dispersive magnetic exciton. For sufficiently strong magnetic exchange, the dispersive exciton can condense, leading to conventional type-I antiferromagnetic (AFM) order which can preempt octupolar order. Our proposal for ferrooctupolar order, with specific results in the context of a model Hamiltonian, provides a comprehensive understanding of thermodynamics, $\mu$SR, X-ray diffraction, and inelastic neutron scattering measurements on a range of cubic $5d^2$ double perovskite materials including Ba$_2$ZnOsO$_6$, Ba$_2$CaOsO$_6$, and Ba$_2$MgOsO$_6$. Our proposal for exciton condensation leading to type-I AFM order may be relevant to materials such as Sr$_2$MgOsO$_6$.
- arXiv:1909.07109 (replaced) [pdf, other]
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Title: Three-Dimensional Active Defect LoopsComments: 12 pages, 4 figuresJournal-ref: Phys. Rev. Lett. 124, 088001 (2020)Subjects: Soft Condensed Matter (cond-mat.soft)
We describe the flows and morphological dynamics of topological defect lines and loops in three-dimensional active nematics and show, using theory and numerical modelling, that they are governed by the local profile of the orientational order surrounding the defects. Analysing a continuous span of defect loop profiles, ranging from radial and tangential twist to wedge $\pm 1/2$ profiles, we show that the distinct geometries can drive material flow perpendicular or along the local defect loop segment, whose variation around a closed loop can lead to net loop motion, elongation or compression of shape, or buckling of the loops. We demonstrate a correlation between local curvature and the local orientational profile of the defect loop, indicating dynamic coupling between geometry and topology. To address the general formation of defect loops in three dimensions, we show their creation via bend instability from different initial elastic distortions.
- arXiv:1909.07407 (replaced) [pdf, other]
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Title: Operator Entanglement in Local Quantum Circuits I: Chaotic Dual-Unitary CircuitsComments: 23 pages, 6 figures; v2 29 pages, 6 figures, improved expositionJournal-ref: SciPost Phys. 8, 067 (2020)Subjects: Statistical Mechanics (cond-mat.stat-mech); High Energy Physics - Theory (hep-th); Chaotic Dynamics (nlin.CD); Quantum Physics (quant-ph)
The entanglement in operator space is a well established measure for the complexity of the quantum many-body dynamics. In particular, that of local operators has recently been proposed as dynamical chaos indicator, i.e. as a quantity able to discriminate between quantum systems with integrable and chaotic dynamics. For chaotic systems the local-operator entanglement is expected to grow linearly in time, while it is expected to grow at most logarithmically in the integrable case. Here we study local-operator entanglement in dual-unitary quantum circuits, a class of "statistically solvable" quantum circuits that we recently introduced. We identify a class of "completely chaotic" dual-unitary circuits where the local-operator entanglement grows linearly and we provide a conjecture for its asymptotic behaviour which is in excellent agreement with the numerical results. Interestingly, our conjecture also predicts a "phase transition" in the slope of the local-operator entanglement when varying the parameters of the circuits.
- arXiv:1909.07410 (replaced) [pdf, other]
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Title: Operator Entanglement in Local Quantum Circuits II: Solitons in Chains of QubitsComments: 22 pages, 1 figure; v2 24 pages, 2 figures, 1 table; v3 24 pages, 2 figuresJournal-ref: SciPost Phys. 8, 068 (2020)Subjects: Statistical Mechanics (cond-mat.stat-mech); High Energy Physics - Theory (hep-th); Quantum Physics (quant-ph)
We provide exact results for the dynamics of local-operator entanglement in quantum circuits with two-dimensional wires featuring ultralocal solitons, i.e. single-site operators which, up to a phase, are simply shifted by the time evolution. We classify all circuits allowing for ultralocal solitons and show that only dual-unitary circuits can feature moving ultralocal solitons. Then, we rigorously prove that if a circuit has an ultralocal soliton moving to the left (right), the entanglement of local operators initially supported on even (odd) sites saturates to a constant value and its dynamics can be computed exactly. Importantly, this does not bound the growth of complexity in chiral circuits, where solitons move only in one direction, say to the left. Indeed, in this case we observe numerically that operators on the odd sublattice have unbounded entanglement. Finally, we present a closed-form expression for the local-operator entanglement entropies in circuits with ultralocal solitons moving in both directions. Our results hold irrespectively of integrability.
- arXiv:1909.07664 (replaced) [pdf, other]
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Title: Tunable wavevector filtering in borophane based normal metal-barrier-normal metal junctionsComments: Ten pages, double column, Eleven figuresJournal-ref: J. Phys.: Condens. Matter 32 (2020) 235301Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We study the transport properties of Dirac electrons across a two-dimensional normal metal-barrier-normal metal (NBN) interfaces in monolayer borophane. We analyse the transmission probability with variation of the width of the barrier region, the incidence energy and transverse momentum. We demonstrate that a gap exists in the transmission probability spectrum and the position, width of transmission gap can be tuned by the barrier strength and transverse momentum respectively. We point out the variation of the ballistic tunneling conductance as a function of the width of the barrier region and incident energy. We find that the oscillatory or decaying nature of the conductance with variation in barrier width depends upon the number of propagating and evanescent modes which are controlled by the incident energy and barrier strength. We show that the conductance as a function of incident energy drops to a minimum value when the incident energy becomes identical to the barrier height and identify that this effect is caused by the presence of evanescent modes inside the barrier. Based on these findings we propose a perfectly tunable wavevector filter for Borophane. We expect our findings posses useful applications in borophane based nano-electronic devices.
- arXiv:1910.03504 (replaced) [pdf, other]
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Title: Random-link matching problems on random regular graphsJournal-ref: J. Stat. Mech. (2020) 033301Subjects: Disordered Systems and Neural Networks (cond-mat.dis-nn); Mathematical Physics (math-ph)
We study the random-link matching problem on random regular graphs, alongside with two relaxed versions of the problem, namely the fractional matching and the so-called "loopy" fractional matching. We estimated the asymptotic average optimal cost using the cavity method. Moreover, we also study the finite-size corrections due to rare topological structures appearing in the graph at large sizes. We estimate these contributions using the cavity approach, and we compare our results with the output of numerical simulations. The analysis also clarifies the meaning of the finite-size contributions appearing in the fully-connected version of the problem, that has been already analyzed in the literature.
- arXiv:1910.07967 (replaced) [pdf, ps, other]
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Title: Studies of Electronic Structure across a Quantum Phase Transition in CeRhSb$_{1-x}$Sn$_x$Journal-ref: European Physical Journal B (2019) 92: 192Subjects: Strongly Correlated Electrons (cond-mat.str-el)
We study an electronic structure of CeRhSb$_{1-x}$Sn$_x$ system, which displays quantum critical transition from a Kondo insulator to a non-Fermi liquid at $x=0.13$. We provide ultraviolet photoelectron spectra of valence band obtained at 12.5 K. Acoherent peak at the Fermi level is not present in the data, but a signal related to 4f$^1$$_{7/2}$ final state is detected. Spectral intensity at the Fermi edge has a general tendency to grow with Sn content. Theoretical calculations of band structure are realized with full-potential local-orbital minimum-basis code using scalar relativistic and full relativistic approach. The calculations reveal a depletion of density of states at the Fermi level for CeRhSb. This gap is shifted above the Fermi energy with increasing Sn content and thus a rise of density of states at the Fermi level is reflected in the calculations. It agrees with metallic properties of compounds with larger $x$. The calculations also yield another important effects of Sn substitution. Band structure is displaced in a direction corresponding to hole doping, although with deviations from a rigid band shift scenario. Lifshitz transitions modify a topology of the Fermi surface a few times and a number of bands crossing the Fermi level increases.
- arXiv:1910.10626 (replaced) [pdf, ps, other]
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Title: Microscopic theory of fractional excitations in gapless bilayer quantum Hall states: semi-quantized quantum Hall statesComments: 33 pagesJournal-ref: SciPost Phys. 8, 031 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Strongly Correlated Electrons (cond-mat.str-el)
We derive the low-energy theory of semi-quantized quantum Hall states, a recently observed class of gapless bilayer fractional quantum Hall states. Our theory shows these states to feature gapless quasiparticles of fractional charge coupled to an emergent Chern-Simons gauge field. These gapless quasiparticles can be understood as composites of electrons and Laughlin-like quasiparticles. We show that semi-quantized quantum Hall states exhibit perfect interlayer drag, host non-Fermi liquid physics, and serve as versatile parent states for fully gapped topological phases hosting anyonic excitations.
- arXiv:1910.11226 (replaced) [pdf]
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Title: Order and Information in the Phases of a Torque-driven Collective SystemAuthors: Wendong Wang, Gaurav Gardi, Vimal Kishore, Lyndon Koens, Donghoon Son, Hunter Gilbert, Palak Harwani, Eric Lauga, Metin SittiComments: 37 pages, 4 main figures, 10 supplementary figuresSubjects: Soft Condensed Matter (cond-mat.soft); Statistical Mechanics (cond-mat.stat-mech); Adaptation and Self-Organizing Systems (nlin.AO); Fluid Dynamics (physics.flu-dyn)
Collective systems across length scales display order in their spatiotemporal patterns. These patterns contain information that correlates with their orders and reflects the system dynamics. Here we show the collective patterns and behaviors of up to 250 micro-rafts spinning at the air-water interface and demonstrate the link between order and information in the collective motion. These micro-rafts display a rich variety of collective behaviors that resemble thermodynamic equilibrium phases such as gases, hexatics, and crystals. Moreover, owing to the unique coupling of magnetic and fluidic forces, a number of collective properties and functions emerge as the micro-rafts interact with magnetic potential and nonmagnetic floating objects. Our findings are relevant for analyzing collective systems in nature and for designing collective robotic systems.
- arXiv:1911.00742 (replaced) [pdf]
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Title: Large-scale optothermal assembly of colloids mediated by a gold microplateComments: 14 pages, 7 figures in main manuscript, 6 figures in supplementary informationSubjects: Optics (physics.optics); Soft Condensed Matter (cond-mat.soft)
Light-activated colloidal assembly and swarming can act as model systems to explore non-equilibrium state of matter. In this context, creating new experimental platforms to facilitate and control two-dimensional assembly of colloidal crystals are of contemporary interest. In this paper, we present an experimental study of assembly of colloidal silica microparticles in the vicinity of a single-crystalline gold microplate evanescently excited by a 532 nm laser beam. The gold microplate acts as a source of heat and establishes a thermal gradient in the system. The created optothermal potential assembles colloids to form a two-dimensional poly-crystal, and we quantify the coordination number and hexagonal packing order of the assembly in such a driven system. Interestingly, we observe variation in assembly-size as a function of excitation-polarization. Furthermore, we observe that the assembly is colloidal-material dependent. Specifically, silica colloids assemble but polystyrene colloids do not, indicating an intricate behaviour of the forces under play. Our work highlights a promising direction in utilizing metallic, single crystalline microstructures that can be harnessed for optothermal colloidal crystal assembly and swarming studies. Our experimental system can be utilized to explore optically driven matter and photophoretic interactions in soft-matter including biological systems such as cells and micro organisms.
- arXiv:1911.03077 (replaced) [pdf, ps, other]
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Title: Complete Spin and Valley Polarization by Total External Reflection from Potential Barriers in Bilayer Graphene and Monolayer Transition Metal DichalcogenidesComments: 5 pages, 5 figures plus supplemental material; minor changes to paper and extra section in supplemental materialSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Transmission through potential barriers in bilayer graphene and transition metal dichalcogenides is shown to be valley asymmetric because of the low symmetry of the total Hamiltonian. In the total external reflection regime the transmission is 100% valley polarized in bilayer graphene and 100% spin and valley polarized in transition metal dichalcogenides, except for exponentially small corrections. The experimental requirements for using this effect to make valley and spin polarizers are described. Symmetry relations that may be useful for detecting valley polarization are given.
- arXiv:1911.04941 (replaced) [pdf, other]
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Title: Detection of Fermi Arcs in Weyl Semimetals through Surface Negative RefractionComments: 9 pages, 7 figures, version 2Journal-ref: Phys. Rev. B 101, 125407 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
One of the main features of Weyl semimetals is the existence of Fermi arc surface states at their surface, which cannot be realized in pure two-dimensional systems in the absence of many-body interactions. Due to the gapless bulk of the semimetal, it is, however, challenging to observe clear signatures from the Fermi arc surface states. Here, we propose to detect such novel surface states via perfect negative refraction that occurs between two adjacent open surfaces with properly orientated Fermi arcs. Specifically, this phenomenon visibly manifests in non-local transport measurement, where the negative refraction generates a return peak in the real-space conductance. This provides a unique signature of the Fermi arc surface states. We discuss the appearance of this peak both in inversion and time-reversal symmetric Weyl semimetals, where the latter exhibits conductance oscillations due to multiple negative refraction scattering events.
- arXiv:1911.05270 (replaced) [pdf, other]
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Title: Variety of order-by-disorder phases in the asymmetric $J_1-J_2$ zigzag ladder: From the delta chain to the $J_1-J_2$ chainComments: 18 pages, 17 figuresJournal-ref: Phys. Rev. B 101, 104407 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el)
We study an asymmetric $J_1$-$J_2$ zigzag ladder consisting of two different spin-$\frac{1}{2}$ antiferromagnetic (AFM; $J_2$, $\gamma J_2>0$) Heisenberg legs coupled by zigzag-shaped ferromagnetic (FM; $J_1<0$) inter-leg interaction. On the basis of density-matrix renormalization group based calculations the ground-state phase diagram is obtained as functions of $\gamma$ and $J_2/|J_1|$. It contains four kinds of frustration-induced ordered phases except a trivial FM phase. Two of the ordered phases are valence bond solid (VBS) with spin-singlet dimerization, which is a rather conventional order by disorder. Still, it is interesting to note that the VBS states possess an Affleck-Kennedy-Lieb-Tasaki-type topological hidden order. The remaining two phases are ferrimagnetic orders, each of which is distinguished by commensurate or incommensurate spin-spin correlation. It is striking that the ferrimagnetic orders are not associated with geometrical symmetry breaking; instead, the global spin-rotation symmetry is broken. In other words, the system lowers its energy via the FM inter-leg interaction by polarizing both of the AFM Heisenberg legs. This is a rare type of order by disorder. Besides, the incommensurate ferrimagnetic state appears as a consequence of the competition between a polarization and a critical Tomonaga-Luttinger-liquid behavior in the AFM Heisenberg legs.
- arXiv:1911.08848 (replaced) [pdf, other]
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Title: Properties of spin-polarized impurities -- ferrons, in the unitary Fermi gasSubjects: Quantum Gases (cond-mat.quant-gas); Superconductivity (cond-mat.supr-con)
A new excitation mode has been predicted to exist in the unitary Fermi gas. It has a form of a spin-polarized impurity, which was dubbed as ferron. It is characterized by a closed nodal surface of the pairing field surrounding a partially spin-polarized superfluid region, where the phase differs by $\pi$. In this paper, we discuss the effect of temperature on the generation of the ferron and the adiabaticity of the spin-polarizing potential together with ferron's ground state properties.
- arXiv:1911.11157 (replaced) [pdf, other]
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Title: Spin liquids in geometrically perfect triangular antiferromagnetsComments: published versionJournal-ref: J. Phys.: Condens. Matter 32, 224004 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el); Materials Science (cond-mat.mtrl-sci)
The cradle of quantum spin liquids, triangular antiferromagnets show strong proclivity to magnetic order and require deliberate tuning to stabilize a spin-liquid state. In this brief review, we juxtapose recent theoretical developments that trace the parameter regime of the spin-liquid phase, with experimental results for Co-based and Yb-based triangular antiferromagnets. Unconventional spin dynamics arising from both ordered and disordered ground states is discussed, and the notion of a geometrically perfect triangular system is scrutinized to demonstrate non-trivial imperfections that may assist magnetic frustration in stabilizing dynamic spin states with peculiar excitations.
- arXiv:1911.12186 (replaced) [pdf]
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Title: Multi-frame Interferometric Imaging with a Femtosecond Stroboscopic Pulse Train for Observing Irreversible PhenomenaAuthors: Dmitro Martynowych, David Veysset, Alexei A. Maznev, Yuchen Sun, Steven E. Kooi, Keith. A. NelsonSubjects: Optics (physics.optics); Materials Science (cond-mat.mtrl-sci)
We describe a high-speed single-shot multi-frame interferometric imaging technique enabling multiple interferometric images with femtosecond exposure time over a 50 ns event window to be recorded following a single laser-induced excitation event. The stroboscopic illumination of a framing camera is made possible through the use of a doubling cavity which produces a femtosecond pulse train that is synchronized to the gated exposure windows of the individual frames of the camera. The imaging system utilizes a Michelson interferometer to extract phase and ultimately displacement information. We demonstrate the method by monitoring laser-induced deformation and the propagation of high-amplitude acoustic waves in a silicon nitride membrane. The method is applicable to a wide range of fast irreversible phenomena such as crack branching, shock-induced material damage, cavitation and dielectric breakdown.
- arXiv:1911.12853 (replaced) [pdf]
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Title: Determination of the trigonal warping orientation in Bernal-stacked bilayer graphene via scanning tunneling microscopyAuthors: Frédéric Joucken, Zhehao Ge, Eberth A. Quezada-López, John L. Davenport, Kenji Watanabe, Takashi Taniguchi, Jairo Velasco JrComments: Accepted in Phys. Rev. BJournal-ref: Phys. Rev. B 101, 161103 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci)
The existence of strong trigonal warping around the K point for the low energy electronic states in multilayer (N$\geq$2) graphene films and graphite is well established. It is responsible for phenomena such as Lifshitz transitions and anisotropic ballistic transport. The absolute orientation of the trigonal warping with respect to the center of the Brillouin zone is however not agreed upon. Here, we use quasiparticle scattering experiments on a gated bilayer graphene/hexagonal boron nitride heterostructure to settle this disagreement. We compare Fourier transforms of scattering interference maps acquired at various energies away from the charge neutrality point with tight-binding-based joint density of states simulations. This comparison enables unambiguous determination of the trigonal warping orientation for bilayer graphene low energy states. Our experimental technique is promising for quasi-directly studying fine features of the band structure of gated two-dimensional materials such as topological transitions, interlayer hybridization, and moir\'e minibands.
- arXiv:1912.03883 (replaced) [pdf, other]
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Title: Intrinsically high thermoelectric figure of merit of half-Heusler ZrRuTeComments: 9 pages, 23 figuresSubjects: Materials Science (cond-mat.mtrl-sci)
The electronic structure and thermoelectric properties of ZrRuTe-based Half-Heusler compounds are studied using density functional theory (DFT) and Boltzmann transport formalism. Based on rigorous computations of electron relaxation time $\tau$ considering electron-phonon interactions and lattice thermal conductivity $\kappa_l$ considering phonon-phonon interactions, we find ZrRuTe to be an intrinsically good thermoelectric material. It has a high power factor of $\sim 2\times 10^{-3}$ W/m-K$^{2}$ and low $\kappa_l\sim 10$ W/m-K at 800 K. The thermoelectric figure of merit $ZT \sim 0.13$ at 800 K is higher than similar other compounds. We have also studied the properties of the material as a function of doping and find the thermoelectric properties to be substantially enhanced for $p$-doped ZrRuTe with the $ZT$ value raised to $\sim 0.2$ at this temperature. The electronic, thermodynamic, and transport properties of the material are thoroughly studied and discussed
- arXiv:1912.04326 (replaced) [pdf, other]
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Title: Phase transition and chaos in charged SYK modelAuthors: Nilakash SorokhaibamComments: 37 pages, minor revision of v2, 16 figuresSubjects: High Energy Physics - Theory (hep-th); Strongly Correlated Electrons (cond-mat.str-el)
We study chaotic-integrable transition and the nature of quantum chaos in SYK model with chemical potential. We use a novel numerical technique to calculate the partition function explicitly. We show the phase transition in the presence of large chemical potential. We also show that a mass-like term consisting of two fermion random interaction (q=2 SYK term) does not give rise to a sharp transition. We find that turning on the chemical potential suppresses the Lyapunov exponent in the chaotic phase exponentially.
- arXiv:1912.07003 (replaced) [pdf, other]
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Title: Boundary Green's function approach for spinful single-channel and multichannel Majorana nanowiresComments: 16 pages, 11 figuresJournal-ref: Phys. Rev. B 101, 094511 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Superconductivity (cond-mat.supr-con)
The boundary Green's function (bGF) approach has been established as a powerful theoretical technique for computing the transport properties of tunnel-coupled hybrid nanowire devices. Such nanowires may exhibit topologically nontrivial superconducting phases with Majorana bound states at their boundaries. We introduce a general method for computing the bGF of spinful multi-channel lattice models for such Majorana nanowires, where the bGF is expressed in terms of the roots of a secular polynomial evaluated in complex momentum space. In many cases, those roots, and thus the bGF, can be accurately described by simple analytical expressions, while otherwise our approach allows for the numerically efficient evaluation of bGFs. We show that from the behavior of the roots, many physical quantities of key interest can be inferred, e.g., the value of bulk topological invariants, the energy dependence of the local density of states, or the spatial decay of subgap excitations. We apply the method to single- and two-channel nanowires of symmetry class D or DIII. In addition, we study the spectral properties of multi-terminal Josephson junctions made out of such Majorana nanowires.
- arXiv:1912.09643 (replaced) [pdf, ps, other]
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Title: Defect charging and resonant levels in half-Heusler Nb$_{1-x}$Ti$_x$FeSbAuthors: Yefan Tian, Farit G. Vagizov, Nader Ghassemi, Wuyang Ren, Hangtian Zhu, Zhiming Wang, Zhifeng Ren, Joseph H. Ross JrComments: 10 pages, 5 figuresSubjects: Materials Science (cond-mat.mtrl-sci)
We report $^{93}$Nb and $^{121}$Sb NMR and $^{57}$Fe M\"{o}ssbauer studies combined with DFT calculations of Nb$_{1-x}$Ti$_x$FeSb ($0\leqslant x \leqslant0.3$), one of the most promising thermoelectric systems for applications above 1000 K. These studies provide local information about defects and electronic configurations in these heavily $p$-type materials. The NMR spin-lattice relaxation rate provides a measure of states within the valence band. With increasing $x$, changes of relaxation rate vs carrier concentration for different substitution fractions indicate the importance of resonant levels which do not contribute to charge transport. The local paramagnetic susceptibility is significantly larger than expected based on DFT calculations, which we discuss in terms of an enhancement of the susceptibility due to a Coulomb enhancement mechanism. The M\"{o}ssbauer spectra of Ti-substituted samples show small departures from a binomial distribution of substituted atoms, while for unsubstituted $p$-type NbFeSb, the amplitude of a M\"{o}ssbauer satellite peak increases vs temperature, a measure of the $T$-dependent charging of a population of defects residing about 30 meV above the valence band edge, indicative of an impurity band at this location.
- arXiv:1912.13425 (replaced) [pdf, other]
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Title: Inflationary routes to Gaussian curved topographyComments: 17 pages, 12 figuresSubjects: Soft Condensed Matter (cond-mat.soft)
Gaussian-curved shapes are obtained by inflating initially flat systems made of two superimposed strong and light thermoplastic impregnated fabric sheets heat-sealed together along a specific network of lines. The resulting inflated structures are light and very strong because they (largely) resist deformation by the intercession of stretch. Programmed patterns of channels vary either discretely through boundaries, or continuously. The former give rise to facetted structures that are in effect non-isometric origami and which cannot unfold as in conventional folded structures, since they present localized angle deficit or surplus. Continuous variation of channel direction in the form of spirals is examined, giving rise to curved shells. We solve the inverse problem consisting in finding a network of seam lines leading to a target axisymmetric shape on inflation. They too have strength from the metric changes that have been pneumatically driven, resistance to change being met with stretch and hence high forces like typical shells .
- arXiv:2001.01042 (replaced) [pdf]
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Title: Observation of spin-motive force in ferrimagnetic GdFeCo alloy filmsJournal-ref: Applied Physics Letters 116, 102402 (2020)Subjects: Materials Science (cond-mat.mtrl-sci); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Non-uniform magnetic structures produce emergent electromagnetic phenomena such as the topological Hall effect and the spin-motive force (SMF). The experimental reports on the SMF, however, are very few and the relationship between the SMF and material parameters is still unclear. In this study, we investigated the SMF in ferrimagnetic GdFeCo alloy films using the spin-torque-induced ferromagnetic resonance method and clarified the relationship. The amplitude of the detected SMF becomes larger than that of the transition metal alloy FeCo by the Gd doping and reaches the maximum near a Gd composition of the boundary between in-plane and perpendicularly magnetized films. According to the analytical calculation, the enhancement is related to the trajectory of the magnetization precession. Moreover, we find that the SMF induced by the magnetic resonance is inversely proportional to the square of the damping constant.
- arXiv:2001.11637 (replaced) [pdf, other]
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Title: Probing the Universality of Topological Defect Formation in a Quantum Annealer: Kibble-Zurek Mechanism and BeyondAuthors: Yuki Bando, Yuki Susa, Hiroki Oshiyama, Naokazu Shibata, Masayuki Ohzeki, Fernando Javier Gómez-Ruiz, Daniel A. Lidar, Adolfo del Campo, Sei Suzuki, Hidetoshi NishimoriSubjects: Quantum Physics (quant-ph); Statistical Mechanics (cond-mat.stat-mech)
The number of topological defects created in a system driven through a quantum phase transition exhibits a power-law scaling with the driving time. This universal scaling law is the key prediction of the Kibble-Zurek mechanism (KZM), and testing it using a hardware-based quantum simulator is a coveted goal of quantum information science. Here we provide such a test using quantum annealing. Specifically, we report on extensive experimental tests of topological defect formation via the one-dimensional transverse-field Ising model on two different D-Wave quantum annealing devices. We find that the quantum simulator results can indeed be explained by the KZM for open-system quantum dynamics with phase-flip errors, with certain quantitative deviations from the theory likely caused by factors such as random control errors and transient effects. In addition, we probe physics beyond the KZM by identifying signatures of universality in the distribution and cumulants of the number of kinks and their decay, and again find agreement with the quantum simulator results. This implies that the theoretical predictions of the generalized KZM theory, which assumes isolation from the environment, applies beyond its original scope to an open system. We support this result by extensive numerical computations. To check whether an alternative, classical interpretation of these results is possible, we used the spin-vector Monte Carlo model, a candidate classical description of the D-Wave device. We find that the degree of agreement with the experimental data from the D-Wave annealing devices is better for the KZM, a quantum theory, than for the classical spin-vector Monte Carlo model, thus favoring a quantum description of the device. Our work provides an experimental test of quantum critical dynamics in an open quantum system, and paves the way to new directions in quantum simulation experiments.
- arXiv:2002.02893 (replaced) [pdf, other]
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Title: Long-lived circular Rydberg states of laser-cooled Rubidium atoms in a cryostatAuthors: Tigrane Cantat-Moltrecht, Rodrigo Cortiñas, Brice Ravon, Paul Méhaignerie, Serge Haroche, Jean-Michel Raimond, Maxime Favier, Michel Brune, Clément SayrinComments: 6 pages, 4 figures T. Cantat-Moltrecht and R. Corti\~nas contributed equally to this workJournal-ref: Phys. Rev. Research 2, 022032 (2020)Subjects: Atomic Physics (physics.atom-ph); Quantum Gases (cond-mat.quant-gas); Quantum Physics (quant-ph)
The exquisite properties of Rydberg levels make them particularly appealing for emerging quantum technologies. The lifetime of low-angular-momentum laser-accessible levels is however limited to a few $100\,\mu\mathrm{s}$ by optical transitions and microwave blackbody radiation (BBR) induced transfers at room temperature. A considerable improvement would be obtained with the few $10\,\mathrm{ms}$ lifetime of circular Rydberg levels in a cryogenic environment reducing the BBR temperature. We demonstrate the preparation of long-lived circular Rydberg levels of laser-cooled Rubidium atoms in a cryostat. We observe a $3.7\,\mathrm{ms}$ lifetime for the circular level of principal quantum number $n=52$. By monitoring the transfers between adjacent circular levels, we estimate in situ the microwave BBR temperature to be $(11\pm 2)\,\mathrm{K}$. The measured atomic coherence time ($270\,\mu\mathrm{s}$) is limited here only by technical magnetic field fluctuations. This work opens interesting perspectives for quantum simulation and sensing with cold circular Rydberg atoms.
- arXiv:2002.04655 (replaced) [pdf, other]
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Title: Spintronics meets density matrix renormalization group: Nonclassical magnetization reversal and entanglement growth due to current-pulse-driven quantum spin torqueComments: 7 pages, 8 figures; one movie available from this https URLSubjects: Strongly Correlated Electrons (cond-mat.str-el); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We introduce time-dependent density matrix renormalization group (tDMRG) as a fully quantum framework for spin-transfer torque (STT), and apply it to understand if recently discovered quantum STT in spin valves at ultralow temperature can lead to magnetization reversal. The conventional Slonczewski-Berger STT, where the magnetization is viewed as a classical vector described by the Landau-Lifshitz-Gilbert equation, occurs only when spin-polarization of injected electrons and localized spins are noncollinear. Conversely, quantum STT occurs when these vectors are collinear but antiparallel, thereby requiring a fully quantum treatment of both electrons and localized spins. Using tDMRG, we simulate time evolution of a many-body quantum state of electrons and localized spins, where the former are injected as spin-polarized current pulse from fermionic leads while the latter comprise a quantum Heisenberg ferromagnetic metallic (FM) spin-1/2 XXZ chain that can also be viewed as a Kondo-Heisenberg chain. The quantum STT reverses the direction of localized spins, but without rotatation from the initial orientation. Such nonclassical reversal is strikingly inhomogeneous across the FM chain and it can be accompanied by reduction of the magnetization associated with localized spins, even to zero at specific locations. This is because quantum STT driven nonequilibrium dynamics generates highly entangled nonequilibrium many-body state of all flowing and localized spins, despite starting from initially separable quantum state of a mundane FM, where mutual information between localized spins at FM edges remains nonzero even at infinite separation as the signature of long-distance entanglement. The growth in time of both the von Neumann entropy of half of the system and global entanglement differentiates between quantum and conventional STT.
- arXiv:2002.05117 (replaced) [pdf, other]
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Title: High order derivatives of Boltzmann microcanonical entropy with an additional conserved quantityAuthors: Ghofrane Bel-Hadj-AissaComments: 9 pagesSubjects: Statistical Mechanics (cond-mat.stat-mech)
In this article, using a known method, a computation is performed of the derivatives of the microcanonical entropy, with respect to the energy up to the 4-th order, using a Laplace transform technique, and adapted it to the case where the total momentum is conserved. The outcome of this computation answers a theoretical question concerning the description of thermodynamics associated with a Hamiltonian flow in presence of an additional conserved quantity besides energy. This is also of practical interest in numerical simulations of the microcanonical thermodynamics associated to classical Hamiltonian flows.
- arXiv:2002.06088 (replaced) [pdf, other]
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Title: Phase Diagram of Solitons in the Polar Phase of a Spin-1 Bose-Einstein CondensateSubjects: Quantum Gases (cond-mat.quant-gas); Other Condensed Matter (cond-mat.other)
We theoretically study the structure of a stationary soliton in the polar phase of spin-1 Bose--Einstein condensate in the presence of quadratic Zeeman effect at zero temperature. The phase diagram of such solitons is mapped out by finding the states of minimal soliton energy in the defining range of polar phase. The states are assorted into normal, anti-ferromagnetic, broken-axisymmetry, and ferromagnetic phases according to the number and spin densities in the core. The order of phase transitions between different solitons and the critical behaviour of relevant continuous transitions are proved within the mean-field theory.
- arXiv:2002.10642 (replaced) [pdf, other]
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Title: The super Frobenius-Schur indicator and finite group gauge theories on pin$^-$ surfacesComments: 11 pages; v2: additional referencesSubjects: Representation Theory (math.RT); Strongly Correlated Electrons (cond-mat.str-el); High Energy Physics - Theory (hep-th); Mathematical Physics (math-ph)
It is well-known that the value of the Frobenius-Schur indicator $|G|^{-1} \sum_{g\in G} \chi(g^2)=\pm1$ of a real irreducible representation of a finite group $G$ determines which of the two types of real representations it belongs to, i.e. whether it is strictly real or quaternionic. We study the extension to the case when a homomorphism $\varphi:G\to \mathbb{Z}/2\mathbb{Z}$ gives the group algebra $\mathbb{C}[G]$ the structure of a superalgebra. Namely, we construct of a super version of the Frobenius-Schur indicator whose value for a real irreducible super representation is an eighth root of unity, distinguishing which of the eight types of irreducible real super representations described in [Wall1964] it belongs to. We also discuss its significance in the context of two-dimensional finite-group gauge theories on pin$^-$ surfaces.
- arXiv:2002.12930 (replaced) [pdf, other]
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Title: Optical Magnetism and Huygens' Surfaces in Arrays of Atoms Induced by Cooperative ResponsesSubjects: Atomic Physics (physics.atom-ph); Quantum Gases (cond-mat.quant-gas); Optics (physics.optics); Quantum Physics (quant-ph)
By utilizing strong optical resonant interactions in arrays of atoms with electric dipole transitions, we show how to synthesize collective optical responses that correspond to those formed by arrays of magnetic dipoles and other multipoles. Optically active magnetism with the strength comparable with that of electric dipole transitions is achieved in collective excitation eigenmodes of the array. By controlling the atomic level shifts, an array of spectrally overlapping, crossed electric and magnetic dipoles can be excited, providing a physical realization of a nearly-reflectionless quantum Huygens' surface with the full $2\pi$ phase control of the transmitted light that allows for extreme wavefront engineering even at a single photon level. We illustrate this by transforming a plane wave into a vortex beam.
- arXiv:2003.03868 (replaced) [pdf, other]
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Title: CP2K: An Electronic Structure and Molecular Dynamics Software Package -- Quickstep: Efficient and Accurate Electronic Structure CalculationsAuthors: Thomas D. Kühne, Marcella Iannuzzi, Mauro Del Ben, Vladimir V. Rybkin, Patrick Seewald, Frederick Stein, Teodoro Laino, Rustam Z. Khaliullin, Ole Schütt, Florian Schiffmann, Dorothea Golze, Jan Wilhelm, Sergey Chulkov, Mohammad Hossein Bani-Hashemian, Valéry Weber, Urban Borstnik, Mathieu Taillefumier, Alice Shoshana Jakobovits, Alfio Lazzaro, Hans Pabst, Tiziano Müller, Robert Schade, Manuel Guidon, Samuel Andermatt, Nico Holmberg, Gregory K. Schenter, Anna Hehn, Augustin Bussy, Fabian Belleflamme, Gloria Tabacchi, Andreas Glöß, Michael Lass, Iain Bethune, Christopher J. Mundy, Christian Plessl, Matt Watkins, Joost VandeVondele, Matthias Krack, Jürg HutterComments: 51 pages, 5 figuresSubjects: Chemical Physics (physics.chem-ph); Materials Science (cond-mat.mtrl-sci); Computational Physics (physics.comp-ph)
CP2K is an open source electronic structure and molecular dynamics software package to perform atomistic simulations of solid-state, liquid, molecular and biological systems. It is especially aimed at massively-parallel and linear-scaling electronic structure methods and state-of-the-art ab-initio molecular dynamics simulations. Excellent performance for electronic structure calculations is achieved using novel algorithms implemented for modern high-performance computing systems. This review revisits the main capabilities of CP2k to perform efficient and accurate electronic structure simulations. The emphasis is put on density functional theory and multiple post-Hartree-Fock methods using the Gaussian and plane wave approach and its augmented all-electron extension.
- arXiv:2003.04659 (replaced) [pdf, other]
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Title: Mediated interactions and photon bound states in an exciton-polariton mixtureComments: 9 pages, 4 figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Quantum Gases (cond-mat.quant-gas); Quantum Physics (quant-ph)
The quest to realise strongly interacting photons remains an outstanding challenge both for fundamental science and for applications. Here, we explore mediated photon-photon interactions in a highly imbalanced two-component mixture of exciton-polaritons in a semiconductor microcavity. Using a theory that takes into account non-perturbative correlations between the excitons as well as strong light-matter coupling, we demonstrate the high tunability of an effective interaction between quasiparticles formed by minority component polaritons interacting with a Bose-Einstein condensate (BEC) of a majority component polaritons. In particular, the interaction, which is mediated by the exchange of sound modes in the BEC can be made strong enough to support a bound state of two quasiparticles. Since these quasiparticles consist partly of photons, this in turn corresponds to a dimer state of photons propagating through the BEC. This gives rise to a new light transmission line where the bound state wave function is directly mapped onto correlations between outgoing photons. Our findings open up new routes for realising highly non-linear optical materials and novel hybrid light-matter quantum systems.
- arXiv:2003.04995 (replaced) [pdf, ps, other]
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Title: The Discrete-Time Facilitated Totally Asymmetric Simple Exclusion ProcessComments: 36 pages, 4 figuresSubjects: Mathematical Physics (math-ph); Statistical Mechanics (cond-mat.stat-mech)
We describe the translation invariant stationary states of the one dimensional discrete-time facilitated totally asymmetric simple exclusion process (F-TASEP). In this system a particle at site $j$ in $Z$ jumps, at integer times, to site $j+1$, provided site $j-1$ is occupied and site $j+1$ is empty. This defines a deterministic noninvertible dynamical evolution from any specified initial configuration on $\{0,1\}^{Z}$. When started with a Bernoulli product measure at density $\rho$ the system approaches a stationary state, with phase transitions at $\rho=1/2$ and $\rho=2/3$. We discuss various properties of these states in the different density regimes $0<\rho<1/2$, $1/2<\rho<2/3$, and $2/3<\rho<1$; for example, we show that the pair correlation $g(j)=\langle\eta(i)\eta(i+j)\rangle$ satisfies, for all $n\in Z$, $\sum_{j=kn+1}^{k(n+1)}g(j)=k\rho^2$, with $k=2$ when $0 \le \rho \le 1/2$ and $k=3$ when $2/3 \le \rho \le 1$, and conjecture (on the basis of simulations) that the same identity holds with $k=6$ when $1/2 \le \rho \le 2/3$. The $\rho<1/2$ stationary state referred to above is also the stationary state for the deterministic discrete-time TASEP at density $\rho$ (with Bernoulli initial state) or, after exchange of particles and holes, at density $1-\rho$.
- arXiv:2003.05369 (replaced) [pdf, ps, other]
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Title: Thermally Tunable Surface Acoustic Wave CavitiesAuthors: André Luiz Oliveira Bilobran, Alberto García-Cristóbal, Paulo Ventura dos Santos, Andrés Cantarero, Mauricio Morais de Lima JrSubjects: Applied Physics (physics.app-ph); Materials Science (cond-mat.mtrl-sci)
We experimentally demonstrate the dynamical tuning of the acoustic field in a surface acoustic wave (SAW) cavity defined by a periodic arrangement of metal stripes on LiNbO3 substrate. Applying a DC voltage to the ends of the metal grid results in a temperature rise due to resistive heating that changes the frequency response of the device up to 0.3%, which can be used to control the acoustic transmission through the structure. The time scale of the switching is demonstrated to be of about 200 ms. In addition, we have also performed finite element simulations of the transmission spectrum of a model system which exhibit a temperature dependence consistent with the experimental data. The advances shown here enable easy, continuous, dynamical control and could be applied for a variety of substrates.
- arXiv:1902.07229 (replaced) [pdf, other]
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Title: Differentiating Majorana from Andreev Bound States in a Superconducting CircuitComments: 9 pages, 3 figuresJournal-ref: Phys. Rev. B 100, 241408(R) (2019)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Superconductivity (cond-mat.supr-con)
We investigate the low-energy theory of a one-dimensional finite capacitance topological Josephson junction. Charge fluctuations across the junction couple to resonant microwave fields and can be used to probe microscopic excitations such as Majorana and Andreev bound states. This marriage between localized microscopic degrees of freedom and macroscopic dynamics of the superconducting phase, leads to unique spectroscopic patterns which allow us to reveal the presence of Majorana fermions among the low-lying excitations.
- arXiv:1904.06461 (replaced) [pdf, ps, other]
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Title: An a posteriori verification method for generalized real-symmetric eigenvalue problems in large-scale electronic state calculationsComments: 15 pages, 7 figuresJournal-ref: J. Comp. Appl. Math. 376, 112830/1-13 (2020)Subjects: Computational Physics (physics.comp-ph); Materials Science (cond-mat.mtrl-sci); Numerical Analysis (math.NA)
An a posteriori verification method is proposed for the generalized real-symmetric eigenvalue problem and is applied to densely clustered eigenvalue problems in large-scale electronic state calculations. The proposed method is realized by a two-stage process in which the approximate solution is computed by existing numerical libraries and is then verified in a moderate computational time. The procedure returns intervals containing one exact eigenvalue in each interval. Test calculations were carried out for organic device materials, and the verification method confirms that all exact eigenvalues are well separated in the obtained intervals. This verification method will be integrated into EigenKernel (https://github.com/eigenkernel/), which is middleware for various parallel solvers for the generalized eigenvalue problem. Such an a posteriori verification method will be important in future computational science.
- arXiv:1905.08225 (replaced) [pdf]
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Title: Independent control of nucleation and layer growth in nanowiresAuthors: Carina B. Maliakkal, Erik K. Mårtensson, Marcus Tornberg, Daniel Jacobsson, Axel R. Persson, Jonas Johansson, Reine Wallenberg, Kimberly A. DickComments: Differences in comparison to previous version: 1) Title- To avoid unlikely but possible confusion of the term 'step-flow' we call it layer growth in this new version. 2) The data and interpretations are mostly the same as in previous version, but presented in a modified perspective. 3) The simulation was refined furtherJournal-ref: ACS Nano, 2020Subjects: Applied Physics (physics.app-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Control of the crystallization process is central to developing novel materials with atomic precision to meet the demands of electronic and quantum technology applications. Semiconductor nanowires grown by the vapor-liquid-solid process are a promising material system in which the ability to form components with structure and composition not achievable in bulk is well-established. Here we use in situ TEM imaging of GaAs nanowire growth to understand the processes by which the growth dynamics are connected to the experimental parameters. We find that two sequential steps in the crystallization process - nucleation and layer growth - can occur on similar time scales and can be controlled independently using different growth parameters. Importantly, the layer growth process contributes significantly to the growth time for all conditions, and will play a major role in determining material properties. The results are understood through theoretical simulations correlating the growth dynamics, liquid droplet and experimental parameters.
- arXiv:1908.11102 (replaced) [pdf, other]
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Title: Field-Effect Transistor based on Surface Negative Refraction in Weyl NanowiresComments: 6 pages, 4 figures, comments are welcomeSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci)
Weyl semimetals are characterized by their bulk Weyl points -- conical band touching points that carry a topological monopole charge -- and Fermi arc states that span between the Weyl points on the surface of the material. Recently, significant progress has been made towards understanding and measuring the physical properties of Weyl semimetals. Yet, potential applications remain relatively sparse. Here, we propose Weyl semimetal nanowires as field-effect transistors, dubbed WEYLFETs. Specifically, applying gradient gate voltage along the nanowire, an electrical field is generated that effectively tilts the open surfaces, thus, varying the relative orientation between Fermi arcs on different surfaces. As a result, perfect negative refraction between adjacent surfaces can occur and longitudinal conductance along the wire is suppressed. The WEYLFET offers a high on/off ratio with low power consumption. Adverse effects due to dispersive Fermi arcs and surface disorder are studied.
- arXiv:1908.11737 (replaced) [pdf, ps, other]
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Title: Lévy walk revisited: Hermite polynomial expansion approachComments: 14 pages, 9 figuresJournal-ref: Journal of Physics A: Mathematical and Theoretical, 53(11), 115002, 2020Subjects: Statistical Mechanics (cond-mat.stat-mech); Mathematical Physics (math-ph)
Integral transform method (Fourier or Laplace transform, etc) is more often effective to do the theoretical analysis for the stochastic processes. However, for the time-space coupled cases, e.g., L\'evy walk or nonlinear cases, integral transform method may fail to be so strong or even do not work again. Here we provide Hermite polynomial expansion approach, being complementary to integral transform method. Some statistical observables of general L\'evy walks are calculated by the Hermite polynomial expansion approach, and the comparisons are made when both the integral transform method and the newly introduced approach work well.
- arXiv:1910.08444 (replaced) [pdf, other]
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Title: Inhomogeneous distribution of particles in co-flow and counterflow quantum turbulenceComments: 8 pages, 4 figures, accepted in Physical Review FluidsJournal-ref: Phys. Rev. Fluids 5, 032601 (2020)Subjects: Other Condensed Matter (cond-mat.other); Fluid Dynamics (physics.flu-dyn)
Particles are today the main tool to study superfluid turbulence and visualize quantum vortices. In this work, we study the dynamics and the spatial distribution of particles in co-flow and counterflow superfluid helium turbulence in the framework of the two-fluid Hall-Vinen-Bekarevich-Khalatnikov (HVBK) model. We perform three-dimensional numerical simulations of the HVBK equations along with the particle dynamics that depends on the motion of both fluid components. We find that, at low temperatures, where the superfluid mass fraction dominates, particles strongly cluster in vortex filaments regardless of their physical properties. At higher temperatures, as viscous drag becomes important and the two components become tightly coupled, the clustering dynamics in the coflowing case approach those found in classical turbulence, while under strong counterflow, the particle distribution is dominated by the quasi-two-dimensionalization of the flow.
- arXiv:1911.06595 (replaced) [pdf]
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Title: Transport Mechanism of Acetamide in Deep Eutectic SolventsJournal-ref: J. Phys. Chem. B 2020, 124, 8, 1509-1520Subjects: Materials Science (cond-mat.mtrl-sci); Soft Condensed Matter (cond-mat.soft)
Over the last couple of decades, deep eutectic solvents (DESs) have emerged as novel alternatives to ionic liquids that are extensively used in synthesis of innovative materials, metal processing, catalysis, etc. However, their usage is limited, primarily because of the large viscosity and poor conductivity. Therefore, an understanding of the molecular origin of these properties is essential to improve their industrial applicability. Here, we present the report of the nanoscopic diffusion mechanism of acetamide in a DES synthesized with lithium perchlorate as studied using neutron scattering and molecular dynamics (MD) simulation techniques. Although, the acetamide based DES (ADES) has remarkably lower freezing point compared to pure acetamide, the molecular mobility is found to be enormously restricted in the former. MD simulation indicates a diffusion model with two distinct processes, corresponding to, long range jump diffusion and localised diffusion within a restricted volume. This model is validated by analysis of neutron scattering data in both molten acetamide and ADES. The long range diffusion process of acetamide is slower by a factor of three in ADES in comparison with molten acetamide. MD simulation reveals that the long range diffusion in ADES is restricted mainly due to the formation of hydrogen bond mediated complexes between the ionic species of the salt and acetamide molecules. Hence, the origin of higher viscosity observed in ADES can be attributed to the complexation. The complex formation also explains the inhibition of the crystallisation process while cooling and thereby results in depression of the freezing point of ADES.
- arXiv:1911.09974 (replaced) [pdf, ps, other]
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Title: Rare events in stochastic processes with sub-exponential distributions and the Big Jump principleComments: 9 pages, 5 figuresJournal-ref: J. Stat. Mech. (2020) 034005Subjects: Statistical Mechanics (cond-mat.stat-mech)
Rare events in stochastic processes with heavy-tailed distributions are controlled by the big jump principle, which states that a rare large fluctuation is produced by a single event and not by an accumulation of coherent small deviations. The principle has been rigorously proved for sums of independent and identically distributed random variables and it has recently been extended to more complex stochastic processes involving L\'evy distributions, such as L\'evy walks and the L\'evy-Lorentz gas, using an effective rate approach. We review the general rate formalism and we extend its applicability to continuous time random walks and to the Lorentz gas, both with stretched exponential distributions, further enlarging its applicability. We derive an analytic form for the probability density functions for rare events in the two models, which clarify specific properties of stretched exponentials.
- arXiv:1912.02009 (replaced) [pdf, other]
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Title: A statistical-inference approach to reconstruct inter-cellular interactions in cell-migration experimentsAuthors: Elena Agliari, Pablo J. Sáez, Adriano Barra, Matthieu Piel, Pablo Vargas, Michele CastellanaJournal-ref: Science Advances 6(11), (2020)Subjects: Cell Behavior (q-bio.CB); Statistical Mechanics (cond-mat.stat-mech); Biological Physics (physics.bio-ph)
Migration of cells can be characterized by two, prototypical types of motion: individual and collective migration. We propose a statistical-inference approach designed to detect the presence of cell-cell interactions that give rise to collective behaviors in cell-motility experiments. Such inference method has been first successfully tested on synthetic motional data, and then applied to two experiments. In the first experiment, cell migrate in a wound-healing model: when applied to this experiment, the inference method predicts the existence of cell-cell interactions, correctly mirroring the strong intercellular contacts which are present in the experiment. In the second experiment, dendritic cells migrate in a chemokine gradient. Our inference analysis does not provide evidence for interactions, indicating that cells migrate by sensing independently the chemokine source. According to this prediction, we speculate that mature dendritic cells disregard inter-cellular signals that could otherwise delay their arrival to lymph vessels.
- arXiv:1912.09220 (replaced) [pdf]
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Title: Limits on gas impermeability of grapheneAuthors: P. Z. Sun, Q. Yang, W. J. Kuang, Y. V. Stebunov, W. Q. Xiong, J. Yu, R. R. Nair, M. I. Katsnelson, S. J. Yuan, I. V. Grigorieva, M. Lozada-Hidalgo, F. C. Wang, A. K. GeimJournal-ref: Nature 579, 229-232 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci)
Despite being only one-atom thick, defect-free graphene is considered to be completely impermeable to all gases and liquids. This conclusion is based on theory and supported by experiments that could not detect gas permeation through micrometre-size membranes within a detection limit of 10^5 to 10^6 atoms per second. Here, using small monocrystalline containers tightly sealed with graphene, we show that defect-free graphene is impermeable with an accuracy of eight to nine orders of magnitude higher than in the previous experiments. We could discern permeation of just a few helium atoms per hour, and this detection limit is also valid for all other tested gases (neon, nitrogen, oxygen, argon, krypton and xenon), except for hydrogen. Hydrogen shows noticeable permeation, even though its molecule is larger than helium and should experience a higher energy barrier. The puzzling observation is attributed to a two-stage process that involves dissociation of molecular hydrogen at catalytically active graphene ripples, followed by adsorbed atoms flipping to the other side of the graphene sheet with a relatively low activation energy of about 1.0 electronvolt, a value close to that previously reported for proton transport. Our work provides a key reference for the impermeability of two-dimensional materials and is important from a fundamental perspective and for their potential applications.
- arXiv:2001.05611 (replaced) [pdf, other]
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Title: Control of polymorphism during epitaxial growth of hyperferroelectric candidate LiZnSb on GaSb (111)BAuthors: Dongxue Du, Patrick J. Strohbeen, Hanjong Paik, Chenyu Zhang, Konrad Genser, Karin M. Rabe, Paul M. Voyles, Darrell G. Schlom, Jason K. KawasakiComments: The following article has been submitted to the Journal of Vacuum Science and Technology. After it is published, it will be found at this https URLJournal-ref: Journal of Vacuum Science & Technology B 38, 022208 (2020)Subjects: Materials Science (cond-mat.mtrl-sci)
A major challenge for ferroelectric devices is the depolarization field, which competes with and often destroys long-range polar order in the limit of ultrathin films. Recent theoretical predictions suggest a new class of materials, termed hyperferroelectics, that should be robust against the depolarization field and enable ferroelectricity down to the monolayer limit. Here we demonstrate the epitaxial growth of hexagonal LiZnSb, one of the hyperferroelectric candidate materials, by molecular-beam epitaxy on GaSb (111)B substrates. Due to the high volatility of all three atomic species, we find that LiZnSb can be grown in an adsorption-controlled window, using an excess zinc flux. Within this window, the desired polar hexagonal phase is stabilized with respect to a competing cubic polymorph, as revealed by X-ray diffraction and transmission electron microscopy measurements. First-principles calculations show that for moderate amounts of epitaxial strain and moderate concentrations of Li vacancies, the cubic LiZnSb phase is lower in formation energy than the hexagonal phase, but only by a few meV per formula unit. Therefore we suggest that kinetics plays a role in stabilizing the desired hexagonal phase at low temperatures. Our results provide a path towards experimentally demonstrating ferroelectricity and hyperferroelectricity in a new class of ternary intermetallic compounds.
- arXiv:2001.05933 (replaced) [pdf, other]
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Title: Quantum transport through a "charge" Kondo circuit: effects of weak repulsive interaction in Luttinger LiquidComments: 10 pages, 2 figuresJournal-ref: Communications in Physics, Vol. 30, No. 1 (2020), pp. 1-10Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Strongly Correlated Electrons (cond-mat.str-el)
We investigate theoretically quantum transport through the "charge" Kondo circuit consisting of the quantum dot (QD) coupled weakly to an electrode at temperature $T+\Delta T$ and connected strongly to another electrode at the reference temperature $T$ by a single-mode quantum point contact (QPC). To account for the effects of Coulomb interaction in the QD-QPC setup operating in the integer quantum Hall regime we describe the edge current in the quantum circuit by Luttinger model characterized by the Luttinger parameter $g$. It is shown that the temperature dependence of both electric conductance $G\propto T^{2/g}$ and thermoelectric coefficient $G_T\propto T^{1+2/g}$ detours from the Fermi-liquid (FL) theory predictions. The behaviour of the thermoelectric power $S=G_T/G\propto T$ in a regime of a single-channel Kondo effect is, by contrast, consistent with the FL paradigm. We demonstrate that the interplay between the mesoscopic Coulomb blockade in QD and weak repulsive interaction in the Luttinger Liquid $g=1-\alpha$ $(\alpha \ll 1)$ results in the enhancement of the thermopower. This enhancement is attributed to suppression of the Kondo correlations in the "charge" circuit by the destructive quantum interference effects.
- arXiv:2002.11441 (replaced) [pdf, other]
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Title: Inelastic electron tunneling in 2H-Ta$_x$Nb$_{1-x}$Se$_2$ evidenced by scanning tunneling spectroscopyAuthors: Xing-Yuan Hou, Fan Zhang, Xin-Hai Tu, Ya-Dong Gu, Meng-Di Zhang, Jing Gong, Yu-Bing Tu, Bao-Tian Wang, Wen-Gang Lv, Hong-Ming Weng, Zhi-An Ren, Gen-Fu Chen, Xiang-De Zhu, Ning Hao, Lei ShanComments: 6 pages, 5 figures. To appear in Physical Review LettersJournal-ref: Phys. Rev. Lett. 124, 106403 (2020)Subjects: Materials Science (cond-mat.mtrl-sci); Superconductivity (cond-mat.supr-con)
We report a detailed study of tunneling spectra measured on 2H-Ta$_x$Nb$_{1-x}$Se$_2$ ($x=0\sim 0.1$) single crystals using a low-temperature scanning tunneling microscope. The prominent gap-like feature unintelligible for a long time was found to be accompanied by some "in-gap" fine structures. By investigating the second-derivative spectra and their temperature and magnetic field dependencies, we were able to prove that inelastic electron tunneling is the origin of these features and obtain the Eliashberg function of 2H-Ta$_x$Nb$_{1-x}$Se$_2$ at atomic scale, providing a potential way to study the local Eliashberg function and phonon spectra of the related transition-metal dichalcogenides.
Crosses
- arXiv:2003.03448 (cross-list from cond-mat.mtrl-sci) [pdf]
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Title: Strengthening the magnetic interactions in pseudobinary first-row transition metal thiocyanates, $\it{M}$(NCS)$_{2}$Authors: Euan N. Bassey, Joseph A. M. Paddison, Evan N. Keyzer, Jeongjae Lee, Pascal Manuel, Ivan da Silva, Siân E. Dutton, Clare P. Grey, Matthew J. CliffeComments: 17 pages, 10 figuresSubjects: Materials Science (cond-mat.mtrl-sci); Strongly Correlated Electrons (cond-mat.str-el)
Understanding the effect of chemical composition on the strength of magnetic interactions is key to the design of magnets with stronger exchange interactions. The magnetic divalent first-row transition metal (TM) thiocyanates are a class of chemically simple layered molecular frameworks. Here, we report two new members of the family, manganese (II) thiocyanate, Mn(NCS)$_{2}$, and iron (II) thiocyanate, Fe(NCS)$_{2}$. Using magnetic susceptibility measurements on these materials and on cobalt (II) thiocyanate and nickel (II) thiocyanate, Co(NCS)$_{2}$ and Ni(NCS)$_{2}$, respectively, we identify significantly stronger net antiferromagnetic interactions between the earlier TM ions-a decrease in the Weiss constant, \theta, from 29 K for Ni(NCS)$_{2}$ to -115 K for Mn(NCS)$_{2}$-a consequence of more diffuse 3d orbitals, increased orbital overlap and increasing numbers of unpaired $\it{t}$$_{2g}$ electrons. We elucidate the magnetic structures of these materials: Mn(NCS)$_{2}$, Fe(NCS)$_{2}$ and Co(NCS)$_{2}$ order into the same antiferromagnetic commensurate ground state, whilst Ni(NCS)$_{2}$ adopts a ground state structure consisting of ferromagnetically ordered layers stacked antiferromagnetically. We show that magnetic molecular frameworks with significantly stronger net exchange interactions can be constructed by using earlier TMs.
Mon, 16 Mar 2020
- arXiv:2003.05948 [pdf, other]
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Title: Topology of superconductors beyond mean-field theoryAuthors: Matthew F. LapaComments: 5+1 pagesSubjects: Superconductivity (cond-mat.supr-con); High Energy Physics - Theory (hep-th); Mathematical Physics (math-ph)
The study of topological superconductivity is largely based on the analysis of mean-field Hamiltonians that violate particle number conservation and have only short-range interactions. Although this approach has been very successful, it is not clear that it captures the topological properties of real superconductors, which are described by number-conserving Hamiltonians with long-range interactions. To address this issue, we study topological superconductivity directly in the number-conserving setting. We focus on a diagnostic for topological superconductivity that compares the fermion parity $\mathcal{P}$ of the ground state of a system in a ring geometry and in the presence of zero vs. $\Phi_{\text{sc}}=\frac{h}{2e} \equiv \pi$ flux of an external magnetic field. A version of this diagnostic exists in any dimension and provides a $\mathbb{Z}_2$ invariant $\nu=\mathcal{P}_0\mathcal{P}_{\pi}$ for topological superconductivity. In this paper we prove that the mean-field approximation correctly predicts the value of $\nu$ for a large family of number-conserving models of spinless superconductors. Our result applies directly to the cases of greatest physical interest, including $p$-wave and $p_x+ip_y$ superconductors in one and two dimensions, and gives strong evidence for the validity of the mean-field approximation in the study of (at least some aspects of) topological superconductivity.
- arXiv:2003.05949 [pdf, other]
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Title: Collisionless kinetic theory for parametrically pumped magnonsSubjects: Statistical Mechanics (cond-mat.stat-mech); Quantum Gases (cond-mat.quant-gas)
We discuss collisionless kinetic equations describing the non-equilibrium dynamics of magnons in a ferromagnet exposed to an oscillating microwave field. Previously, this problem has been treated within the so-called "S-theory" where the collision integral in the kinetic equation for the magnon distribution is either neglected or taken into account phenomenologically via an effective relaxation time. However, the possibility of magnon condensation has not been included in S-theory. Moreover, the momentum integrations appearing in the magnon self-energies are usually decoupled by retaining only the term where the loop momentum is equal to the external momentum. In this work we critically examine the accuracy of these approximations and develop the proper extensions of S-theory. We show that these extensions can significantly modify the time evolution of the magnon distribution.
- arXiv:2003.05954 [pdf, other]
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Title: Emergent QCD$_3$ Quantum Phase Transitions of Fractional Chern InsulatorsComments: 17+2 pages, 1 figureSubjects: Strongly Correlated Electrons (cond-mat.str-el); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); High Energy Physics - Theory (hep-th)
Motivated by the recent work of QED$_3$-Chern-Simons quantum critical points of fractional Chern insulators (Phys. Rev. X \textbf{8}, 031015, (2018)), we study its non-Abelian generalizations, namely QCD$_3$-Chern-Simons quantum phase transitions of fractional Chern insulators. These phase transitions are described by Dirac fermions interacting with non-Abelian Chern-Simons gauge fields ($U(N)$, $SU(N)$, $USp(N)$, etc.). Utilizing the level-rank duality of Chern-Simons gauge theory and non-Abelian parton constructions, we discuss two types of QCD$_3$ quantum phase transitions. The first type happens between two Abelian states in different Jain sequences, as opposed to the QED3 transitions between Abelian states in the same Jain sequence. A good example is the transition between $\sigma^{xy}=1/3$ state and $\sigma^{xy}=-1$ state, which has $N_f=2$ Dirac fermions interacting with a $U(2)$ Chern-Simons gauge field. The second type is naturally involving non-Abelian states. For the sake of experimental feasibility, we focus on transitions of Pfaffian-like states, including the Moore-Read Pfaffian, anti-Pfaffian, particle-hole Pfaffian, etc. These quantum phase transitions could be realized in experimental systems such as fractional Chern insulators in graphene heterostructures.
- arXiv:2003.05957 [pdf, other]
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Title: Integrable Matrix Models in Discrete Space-TimeComments: 60 pages, 10 figures, 1 tableSubjects: Statistical Mechanics (cond-mat.stat-mech); High Energy Physics - Theory (hep-th); Mathematical Physics (math-ph)
We introduce a class of integrable dynamical systems of interacting classical matrix-valued fields propagating on a discrete space-time lattice, realized as many-body circuits built from elementary symplectic two-body maps. The models provide an efficient integrable Trotterization of non-relativistic $\sigma$-models with complex Grassmannian manifolds as target spaces, including, as special cases, the higher-rank analogues of the Landau--Lifshitz field theory on complex projective spaces. As an application, we study transport of Noether charges in canonical local equilibrium states. We find a clear signature of superdiffusive behavior in the Kardar--Parisi--Zhang universality class, irrespectively of the chosen underlying global unitary symmetry group and the quotient structure of the compact phase space, providing a strong indication of superuniversal physics.
- arXiv:2003.05966 [pdf, other]
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Title: Hypersensitive tunable Josephson escape sensor for gigahertz astronomyAuthors: Federico Paolucci, Nadia Ligato, Vittorio Buccheri, Gaia Germanese, Pauli Virtanen, Francesco GiazottoComments: 13 pages, 8 figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Superconductivity (cond-mat.supr-con)
Sensitive photon detection in the gigahertz band constitutes the cornerstone to study different phenomena in astronomy, such as radio burst sources, galaxy formation, cosmic microwave background, axions, comets, gigahertz-peaked spectrum radio sources and supermassive black holes. Nowadays, state of the art detectors for astrophysics are mainly based on transition edge sensors and kinetic inductance detectors. Overall, most sensible nanobolometers so far are superconducting detectors showing a noise equivalent power (NEP) as low as 2x10-20 W/Hz1/2. Yet, fast thermometry at the nanoscale was demonstrated as well with Josephson junctions through switching current measurements. In general, detection performance are set by the fabrication process and limited by used materials. Here, we conceive and demonstrate an innovative tunable Josephson escape sensor (JES) based on the precise current control of the temperature dependence of a fully superconducting one-dimensional nanowire Josephson junction. The JES might be at the core of future hypersensitive in situ-tunable bolometers or single-photon detectors working in the gigahertz regime. Operated as a bolometer the JES points to a thermal fluctuation noise (TFN) NEP_TFN 1x10-25 W/Hz1/2, which as a calorimeter bounds the frequency resolution above 2 GHz, and resolving power below 40 at 50 GHz, as deduced from the experimental data. Beyond the obvious applications in advanced ground-based and space telescopes for gigahertz astronomy, the JES might represent a breakthrough in several fields of quantum technologies ranging from subTHz communications and quantum computing to cryptography and quantum key distribution.
- arXiv:2003.05971 [pdf, other]
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Title: Semi adsorption-controlled growth window for half Heusler FeVSb epitaxial filmsAuthors: Estiaque H. Shourov, Ryan Jacobs, Wyatt A. Behn, Zachary J. Krebs, Chenyu Zhang, Patrick J. Strohbeen, Dongxue Du, Paul M. Voyles, Victor W. Brar, Dane D. Morgan, Jason K. KawasakiSubjects: Materials Science (cond-mat.mtrl-sci)
The electronic, magnetic, thermoelectric, and topological properties of Heusler compounds (composition $XYZ$ or $X_2 YZ$) are highly sensitive to stoichiometry and defects. Here we establish the existence and experimentally map the bounds of a \textit{semi} adsorption-controlled growth window for semiconducting half Heusler FeVSb films, grown by molecular beam epitaxy (MBE). We show that due to the high volatility of Sb, the Sb stoichiometry is self-limiting for a finite range of growth temperatures and Sb fluxes, similar to the growth of III-V semiconductors such as GaSb and GaAs. Films grown within this window are nearly structurally indistinguishable by X-ray diffraction (XRD) and reflection high energy electron diffraction (RHEED). The highest electron mobility and lowest background carrier density are obtained towards the Sb-rich bound of the window, suggesting that Sb-vacancies may be a common defect. Similar \textit{semi} adsorption-controlled bounds are expected for other ternary intermetallics that contain a volatile species $Z=$\{Sb, As, Bi\}, e.g., CoTiSb, LuPtSb, GdPtBi, and NiMnSb. However, outstanding challenges remain in controlling the remaining Fe/V ($X/Y$) transition metal stoichiometry.
- arXiv:2003.05972 [pdf, other]
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Title: Skyrmion Dynamics and Transverse Mobility: Skyrmion Hall Angle Reversal on 2D Periodic Substrates with dc and Biharmonic ac DrivesComments: 12 pages, 17 figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Soft Condensed Matter (cond-mat.soft); Superconductivity (cond-mat.supr-con)
We numerically examine the dynamics of a skyrmion interacting with a two-dimensional periodic substrate under dc and biharmonic ac drives. We show that the Magnus force of the skyrmion produces circular orbits that can resonate with the ac drive and the periodicity of the substrate to create quantized motion both parallel and perpendicular to the dc drive. The skyrmion Hall angle exhibits a series of increasing and/or decreasing steps along with strongly fluctuating regimes. In the phase locked regimes, the skyrmion Hall angle is constant and the skyrmion motion consists of periodic orbits encircling an integer number of obstacles per every or every other ac drive cycle. We also observe phases in which the skyrmion moves at $90^\circ$ with respect to the driving direction even in the presence of damping, a phenomenon called absolute transverse mobility that can exhibit reentrance as a function of dc drive. When the biharmonic ac drives have different amplitudes, in the two directions we find regimes in which the skyrmion Hall angle shows a sign reversal from positive to negative, as well as a reentrant pinning effect in which the skyrmion is mobile at low drives but becomes pinned at higher drives. These behaviors arise due to the combination of the Magnus force with the periodic motion of the skyrmions, which produce Shapiro steps, directional locking, and ratchet effects.
- arXiv:2003.06031 [pdf, other]
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Title: Analysis and forecast of COVID-19 spreading in China, Italy and FranceSubjects: Populations and Evolution (q-bio.PE); Statistical Mechanics (cond-mat.stat-mech); Adaptation and Self-Organizing Systems (nlin.AO)
In this note we analyze the temporal dynamics of the coronavirus disease 2019 outbreak in China, Italy and France in the time window $22/01-09/03/2020$. A first analysis of simple day-lag maps points to some universality in the epidemic spreading, suggesting that simple mean-field models can be meaningfully used to gather a quantitative picture of the epidemic spreading, and notably the height and time of the peak of confirmed infected individuals.
The analysis of the same data within a simple susceptible-(confirmed) infected-recovered-deaths model indicates that the kinetic parameter that describes the rate of recovery seems to be the same, irrespective of the country, while the infection and death rates appear to be more variable. The model places the peak in Italy around March 20$^{\rm th}$ 2020, with a maximum number of confirmed infected individuals of about 16,000. - arXiv:2003.06046 [pdf, other]
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Title: Height fluctuations in homoepitaxial thin film growth: A numerical studyJournal-ref: Phys. Rev. Research 2, 013385 (2020)Subjects: Statistical Mechanics (cond-mat.stat-mech); Computational Physics (physics.comp-ph)
We report on the investigation of height distributions (HDs) and spatial covariances of two-dimensional surfaces obtained from extensive numerical simulations of the celebrated Clarke-Vvedensky (CV) model for homoepitaxial thin film growth. In this model, the effect of temperature, deposition flux, and strengths of atom-atom interactions are encoded in two parameters: the diffusion to deposition ratio $R=D/F$ and $\varepsilon$, which is related to the probability of an adatom "breaking" a lateral bond. We demonstrate that the HDs present a strong dependence on both $R$ and $\varepsilon$, and even after the deposition of $10^5$ monolayers (MLs) they are still far from the asymptotics in some cases. For instance, the temporal evolution of the HDs' skewness (kurtosis) displays a pronounced minimum (maximum), for small $R$ and $\varepsilon$, and only at long times it passes to increase (decrease) toward its asymptotic value. However, it is hard to determine whether they converge to a single value or different nonuniversal ones. For large $R$ and/or $\varepsilon$, on the other hand, these quantities clearly converge to the values expected for the Villain-Lai-Das Sarma (VLDS) universality class. A similar behavior is observed in the spatial covariances, but with weaker finite-time effects, so that rescaled curves of them collapse quite well with the one for the VLDS class at long times. Simulations of a model with limited mobility of particles, which captures some essential features of the CV model in the limit of irreversible aggregation ($\varepsilon=0$), reveal a similar scenario. Overall, these results point out that the study of fluctuations in homoepitaxial thin films' surfaces can be a very difficult task and shall be performed very carefully, once typical experimental films have $\lesssim 10^4$ MLs, so that their HDs and covariances can be in the realm of transient regimes.
- arXiv:2003.06062 [pdf, other]
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Title: Efficient Compression Of The Environment Of An Open Quantum SystemComments: 11 pages, 5 figuresSubjects: Strongly Correlated Electrons (cond-mat.str-el); Chemical Physics (physics.chem-ph); Computational Physics (physics.comp-ph)
In order to simulate open quantum systems, many approaches (such as Hamiltonian-based solvers in dynamical mean-field theory) aim for a reproduction of a desired environment spectral density in terms of a discrete set of bath states, mimicking the open system as a larger closed problem. Existing strategies to find a compressed representation of the environment for this purpose can be numerically demanding, or lack the compactness and systematic improvability required for an accurate description of the system propagator. We propose a method in which bath orbitals are constructed explicitly by an algebraic construction based on the Schmidt-decomposition of response wave functions, efficiently and systematically compressing the description of the full environment. These resulting bath orbitals are designed to directly reproduce the system Green's function, not hybridization, which allows for consideration of the relevant system energy scales to optimally model. This results in an accurate and efficient truncation of the environment, with applications in a wide range of numerical simulations of open quantum systems.
- arXiv:2003.06070 [pdf]
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Title: To modulate thermal conductivity of poly(vinylidene fluoride) by electric fieldsAuthors: Shichen Deng, Xiaoxiang Yu, Jiale Yuan, Dengke Ma, Yuwen Huang, Rencai Ji, Guangzu Zhang, Nuo YangSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci)
Phonon engineering focusing on the heat transport modulation on the atomic scale has arisen in recent decades. In addition to the reported ways of phonon engineering like controlling material size, doping and mechanical stretching, in this work, we show that electric field can also modulate heat transport. Thermal conductivity of poly(vinylidene fluoride) (PVDF), one typical electroactive ferroelectric polymer, is investigated by molecular dynamics simulation. Interestingly, the electric-field-poled PVDF array shows higher thermal conductivity than that of unpoled one along all three directions, and the enhancement ratio approach 225% along the polarization direction. The morphology and phonon property analysis reveal that the enhancement of thermal conductivity arises from the higher inter-chain lattice order, stronger inter-chain interaction, higher phonon group velocity and suppressed phonon scattering in poled PVDF. Moreover, it shows that the enhancement is more obvious at lower temperature. Investigation on thermal conductivity versus electric field shows that the enhancement is transient after the field exceeds the threshold. Our study offers a new strategy of phonon engineering.
- arXiv:2003.06083 [pdf, other]
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Title: An Ultra-Compact X-Ray Free-Electron LaserAuthors: J. B. Rosenzweig, N. Majernik, R. R. Robles, G. Andonian, O. Camacho, A. Fukasawa, A. Kogar, G. Lawler, Jianwei Miao, P. Musumeci, B. Naranjo, Y. Sakai, R. Candler, B. Pound, C. Pellegrini, C. Emma, A. Halavanau, J. Hastings, Z. Li, M. Nasr, S. Tantawi, P. Anisimov, B. Carlsten, F. Krawczyk, E. Simakov, L. Faillace, M. Ferrario, B. Spataro, S. Karkare, J. Maxson, Y. Ma, J. Wurtele, A. Murokh, A. Zholents, A. Cianchi, D. CoccoComments: 58 pages, 19 figuresSubjects: Accelerator Physics (physics.acc-ph); Materials Science (cond-mat.mtrl-sci); High Energy Physics - Experiment (hep-ex); Applied Physics (physics.app-ph); Biological Physics (physics.bio-ph)
In the field of beam physics, two frontier topics have taken center stage due to their potential to enable new approaches to discovery in a wide swath of science. These areas are: advanced, high gradient acceleration techniques, and x-ray free electron lasers (XFELs). Further, there is intense interest in the marriage of these two fields, with the goal of producing a very compact XFEL. In this context, recent advances in high gradient radio-frequency cryogenic copper structure research have opened the door to the use of surface electric fields between 250 and 500 MV/m. Such an approach is foreseen to enable a new generation of photoinjectors with six-dimensional beam brightness beyond the current state-of-the-art by well over an order of magnitude. This advance is an essential ingredient enabling an ultra-compact XFEL (UC-XFEL). In addition, one may accelerate these bright beams to GeV scale in less than 10 meters. Such an injector, when combined with inverse free electron laser-based bunching techniques can produce multi-kA beams with unprecedented beam quality, quantified by ~50 nm-rad normalized emittances. These beams, when injected into innovative, short-period (1-10 mm) undulators uniquely enable UC-XFELs having footprints consistent with university-scale laboratories. We describe the architecture and predicted performance of this novel light source, which promises photon production per pulse of a few percent of existing XFEL sources. We review implementation issues including collective beam effects, compact x-ray optics systems, and other relevant technical challenges. To illustrate the potential of such a light source to fundamentally change the current paradigm of XFELs with their limited access, we examine possible applications in biology, chemistry, materials, atomic physics, industry, and medicine which may profit from this new model of performing XFEL science.
- arXiv:2003.06089 [pdf, other]
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Title: Towards the ideal glass transition by pinning in a dimer-polymer mixtureAuthors: Genki Kikumoto, Naohiro Torii, C. Patrick Royall, Haruhiko Yao, Yasuo Saruyama, Soichi TatsumiComments: 5 pages, 3 figuresSubjects: Soft Condensed Matter (cond-mat.soft)
We use a mixture of a polymer and its dimer to control dynamics in a manner inspired by \emph{pinning} a fraction of the system. In our system of $\alpha$-methyl styrene, where the polymer has a glass transition at higher temperature than the dimer, at intermediate temperatures, the polymer acts to "pin" the dimer. Within this temperature range, we obtain a measure of the point-to-set length and show that the degree of "pinning" has a profound effect on the fragility of the system. In particular, we find fragile behaviour implying a large degree of co-operativity in the case of low pinning fraction, while at a high level of pinning, we find strong liquid behaviour, indicating a small degree of co-operativity.
- arXiv:2003.06095 [pdf, other]
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Title: Pseudogap regime of a strongly interacting two-dimensional Fermi gas with and without confinement-induced effect range of interactionsComments: 11 pages, 8 figuresSubjects: Quantum Gases (cond-mat.quant-gas)
We investigate theoretically the many-body pairing of a strongly correlated two-dimensional Fermi gas with and without negative confinement-induced effective range. Using a strong-coupling effective field theory in the normal state, we show that the specific heat at constant volume can be used as a characteristic indicator of the crossover from the normal Fermi liquid to the pseudogap state in two dimensions. We calculate the pseudogap formation temperature through the specific heat at constant volume, examining the role of a negative confinement-induced effective range on many-body pairing above the superfluid transition. We compare our results with and without effective range to the recent experimental measurement performed with radio-frequency spectroscopy in Murthy et al.[Science359, 452-455 (2018)]. Although a good qualitative agreement is found, we are not able to discriminate the effect of the confinement-induced effect range in the experimental data.
- arXiv:2003.06098 [pdf, ps, other]
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Title: Evolutionary construction of formation energy convex hull: Practical scheme and application to carbon-hydrogen binary systemSubjects: Materials Science (cond-mat.mtrl-sci)
We present an evolutionary construction technique of formation energy convex hull to search for thermodynamically stable compounds. In this technique, candidates with a wide variety of chemical compositions and crystal structures are created by systematically applying evolutionary operators, "mating", "mutation", and "adaptive mutation", to two target compounds, and the convex hull is directly updated through the evolution. We applied the technique to carbon-hydrogen binary system at 10 GPa and obtained 15 hydrocarbons within the convex hull distance less than 0.5 mRy/atom: graphane, polybutadiene, polyethylene, butane, ethane, methane, three molecular compounds of ethane and methane, and six molecular compounds of methane and hydrogen. These results suggest that our evolutionary construction technique is useful for the exploration of stable phases under extreme conditions and the synthesis of new compounds.
- arXiv:2003.06102 [pdf, other]
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Title: Clogging in bidirectional suspension flowSubjects: Soft Condensed Matter (cond-mat.soft)
The sudden arrest of motion due to confinement is commonly observed via the clogging transition in the flow of particles through a constriction. We present results of a simple experiment to elucidate a similar transition in the bidirectional flow of two species in which two species of macroscopic particles with different densities are confined in a tube and suspended in a fluid of intermediate density. Counterflowing grains serve as mobile obstacles and clogging occurs without arch formation due to confinement. We measure the clogging or jamming probability $J$ as a function of number of particles of each species $N$ in a fixed channel length for channel widths $D = $ 3$-$7$d$, where $d$ is the particle diameter. $J(N)$ exhibits a sigmoidal dependence and collapses on a single curve $J(N/D^3)$ indicating the transition occurs at a critical density. Data is well-fit by a probabilistic model motivated by prior constriction flows which assumes grains enter the clogging region with a fixed probability to produce a clogging state. A quasi-two-dimensional experiment provides insight into the interface shape and and we identify a Rayleigh-Taylor instability at large channel widths.
- arXiv:2003.06110 [pdf]
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Title: Old Story New Tell: The Graphite to Diamond Transition RevisitedComments: 35 pages, 5 figuresSubjects: Materials Science (cond-mat.mtrl-sci)
Graphite and diamond are two well-known allotropes of carbon with distinct physical properties due to different atomic connectivity. Graphite has a layered structure in which the honeycomb carbon sheets can easily glide, while atoms in diamond are strongly bonded in all three dimensions. The transition from graphite to diamond has been a central subject in physical science. One way to turn graphite into diamond is to apply the high pressure and high temperature (HPHT) conditions. However, atomistic mechanism of this transition is still under debate. From a series of large-scale molecular dynamics (MD) simulations, we report a mechanism that the diamond nuclei originate at the graphite grain boundaries and propagate in two preferred directions. In addition to the widely accepted [001] direction, we found that the growth along [120] direction of graphite is even faster. In this scenario, cubic diamond (CD) is the kinetically favorable product, while hexagonal diamond (HD) would appear as minor amounts of twinning structures in two main directions. Following the crystallographic orientation relationship, the coherent interface t-(100)gr//(11-1)cd + [010]gr//[1-10]cd was also confirmed by high-resolution transmission electron microscopy (HR-TEM) experiment. The proposed phase transition mechanism does not only reconcile the longstanding debate regarding the role of HD in graphite-diamond transition, but also yields the atomistic insight into microstructure engineering via controlled solid phase transition.
- arXiv:2003.06111 [pdf]
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Title: Ion transport across solid-state ion channels perturbed by directed strainSubjects: Applied Physics (physics.app-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Biological Physics (physics.bio-ph)
We combine quantum-chemical calculations and molecular dynamics simulations to consider aqueous ion flow across non-axisymmetric nanopores in monolayer graphene and MoS$_2$. When the pore-containing membrane is subject to uniaxial tensile strains applied in various directions, the corresponding permeability exhibits considerable directional dependence. This anisotropy is shown to arise from directed perturbations of the local electrostatics by the corresponding pore deformation, as enabled by the pore edge geometries and atomic compositions. By considering nanopores with ionic permeability that depends on the strain direction, we present model systems that may yield a detailed understanding of the structure-function relationship in solid-state and biological ion channels. Specifically, the observed anisotropic effects potentially enable the use of permeation measurements across strained membranes to obtain directional profiles of ion-pore energetics as contributed by groups of atoms or even individual atoms at the pore edge. The resulting insight may facilitate the development of subnanoscale pores with novel functionalities arising from locally asymmetric pore edge features.
- arXiv:2003.06118 [pdf, other]
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Title: Holographic entanglement renormalisation of topological order in a quantum liquidComments: 43 pages, 24 figuresSubjects: Strongly Correlated Electrons (cond-mat.str-el); High Energy Physics - Theory (hep-th); Quantum Physics (quant-ph)
We introduce a novel momentum space entanglement renormalization group (MERG) scheme for the topologically ordered (T.O.) ground state of the 2D Hubbard model on a square lattice (arxiv:1802.06528) using a unitary quantum circuit comprised of non-local unitary gates. At each MERG step, the unitary quantum circuit disentangles a set of electronic states, thereby transforming the tensor network representation of the many-particle state. By representing the non-local unitary gate as a product of two-qubit disentangler gates, we provide an entanglement holographic mapping (EHM) representation for MERG. Using entanglement based measures from quantum information theory and complex network theory, we study the emergence of topological order in the bulk of the EHM. We also demonstrate that the MERG is equivalent to a stabiliser quantum error correcting code. The MERG reveals very different holographic entanglement features for the normal metallic and topologically ordered states of the 2D Hubbard model, clarifying the essence of the entanglement phase transition that separates the two phases. We perform an information theoretic analysis of the EHM network, demonstrating that the information bottleneck principle is responsible for the distillation of entanglement features in the heirarchical structure of the EHM network. As a result, we construct a deep neural network (DNN) architecture based on our EHM network, and employ it for predicting the onset of topological order. We also demonstrate that the DNN is capable of distinguishing between the topologically ordered and gapless normal metallic phases.
- arXiv:2003.06134 [pdf, other]
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Title: Generalization of the hierarchical equations of motion theory for efficient calculations with arbitrary correlation functionsComments: 18 pages, 6 figuresJournal-ref: J. Chem. Phys. 152, 204101 (2020)Subjects: Chemical Physics (physics.chem-ph); Statistical Mechanics (cond-mat.stat-mech); Quantum Physics (quant-ph)
The hierarchical equations of motion (HEOM) theory is one of the standard methods to rigorously describe open quantum dynamics coupled to harmonic environments. Such a model is used to capture non-Markovian and non-perturbative effects of environments appearing in ultra-fast phenomena. In the regular framework of the HEOM theory, the environment correlation functions are restricted into linear combinations of exponential functions. In this article, we present a new formulation of the HEOM theory including treatments of non-exponential correlation functions, which enables us to describe general environmental effects more efficiently and stably than the original theory and other generalizations. The library and its Python binding we developed to perform simulations based on our approach, named LibHEOM and PyHEOM respectively, are provided as supplementary material.
- arXiv:2003.06220 [pdf, other]
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Title: Phonon anharmonicity enhances the $T_c$ of BCS-type superconductorsComments: 7 pages, 4 figures including supplemental materialSubjects: Superconductivity (cond-mat.supr-con); Disordered Systems and Neural Networks (cond-mat.dis-nn); Materials Science (cond-mat.mtrl-sci)
A theory of superconductivity is presented where the effect of anharmonicity, as entailed in the acoustic phonon damping, is explicitly considered in the pairing mechanism. The gap equation is solved including diffusive Akhiezer damping for longitudinal acoustic phonons, with a damping coefficient which can be directly related to the Gr{\"u}neisen parameter and hence to the anharmonic coefficients in the interatomic potential. The results show that the increase of anharmonicity has a strikingly non-monotonic effect on the critical temperature $T_{c}$. The optimal damping coefficient yielding maximum $T_c$ is set by the velocity of the bosonic mediator. This theory may open up unprecedented opportunities for material design where $T_{c}$ may be tuned via the anharmonicity of the interatomic potential, and presents implications for the superconductivity in the recently discovered hydrides, where anharmonicity is very strong and for which the Akhiezer damping is especially relevant.
- arXiv:2003.06224 [pdf]
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Title: Comparative analysis of machine learning models for Ammonia Capture of Ionic LiquidsComments: 44 pages, 12 figuresSubjects: Soft Condensed Matter (cond-mat.soft); Machine Learning (cs.LG)
Industry uses various solvents in the processes of refrigeration and ventilation. Among them, the Ionic liquids (ILs) as the relatively new solvents, are known for their proven eco-friendly characteristics. In this research, a comprehensive literature review was carried out to deliver an insight into the ILs and the prediction models used for estimating the ammonia solubility in ILs. Furthermore, a number of advanced machine learning methods, i.e. multilayer perceptron (MLP) and a combination of particle swarm optimization (PSO) and adaptive neuro-fuzzy inference system (ANFIS) models are used to estimate the solubility of ammonia in various ionic liquids. Affecting parameters were molecular weight, critical temperature and pressure of ILs. Furthermore, the salability is also predicted using the two-equation of states. Down the line, some comparisons were drawn between experimental and modeling results which is rarely done. The study shows that the equations of states are not able estimate the solubility of ammonia accurately, by contrast, artificial intelligence methods have produced promising results.
- arXiv:2003.06225 [pdf, other]
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Title: Normal modes of vibrations around Hubble flow in JelliumAuthors: Eugene B. KolomeiskyComments: 9 pages,1 figure, minor changes, version to be published in Pays. Rev. BJournal-ref: Phys. Rev. B 101, 174304 (2020)Subjects: Statistical Mechanics (cond-mat.stat-mech); General Relativity and Quantum Cosmology (gr-qc)
A macroscopic Coulomb system of identical charged particles with or without a compensating background charge can evolve maintaining spatial homogeneity and isotropy that mimic the cosmological evolution of a universe with repulsive gravity. Here we study dynamics of small perturbations on the background of the corresponding Hubble flow by analyzing its normal modes of vibrations. Arbitrary disturbance of the flow can be resolved into two electro-acoustic, two vortical, and one entropic modes whose dynamics is investigated. Specifically, in the zero pressure or long-wavelength limits perturbations of density and velocity evolve in a manner that is independent of the form of the initial disturbance. The same conclusion applies to vortical perturbations of the velocity for arbitrary pressure while entropic perturbations are advected by the Hubble flow. Without the background charge the underlying Hubble flow describes a Coulomb explosion whose stability with respect to small disturbances is also demonstrated.
- arXiv:2003.06228 [pdf, other]
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Title: Iterative Retraining of Quantum Spin Models Using Recurrent Neural NetworksAuthors: Christopher RothComments: 7 pages, 4 figuresSubjects: Computational Physics (physics.comp-ph); Disordered Systems and Neural Networks (cond-mat.dis-nn); Strongly Correlated Electrons (cond-mat.str-el)
Modeling quantum many-body systems is enormously challenging due to the exponential scaling of Hilbert dimension with system size. Finding efficient compressions of the wavefunction is key to building scalable models. Here, we introduce iterative retraining, an approach for simulating bulk quantum systems that uses recurrent neural networks (RNNs). By mapping translations in the lattice vector to the time index of an RNN, we are able to efficiently capture the near translational invariance of large lattices. We show that we can use this symmetry mapping to simulate very large systems in one and two dimensions. We do so by 'growing' our model, iteratively retraining the same model on progressively larger lattices until edge effects become negligible. We argue that this scheme generalizes more naturally to higher dimensions than Density Matrix Renormalization Group.
- arXiv:2003.06229 [pdf, other]
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Title: Microfluidic In Situ Measurement of Poisson's Ratio of HydrogelsJournal-ref: Micromachines 2020, 11(3), 318;Subjects: Soft Condensed Matter (cond-mat.soft)
Being able to precisely characterize the mechanical properties of soft microparticles is essential for numerous situations from the understanding of the flow of biological fluids to the development of soft micro-robots. Here we present a simple measurement technique for the Poisson's ratio of soft micron-sized hydrogels in the presence of a surrounding liquid. This methods relies on the measurement of the deformation in two orthogonal directions of a rectangular hydrogel slab compressed uni-axially inside a microfluidic channel. Due to the in situ character of the method, the sample does not need to be dried, allowing for the measurement of the mechanical properties of swollen hydrogels. Using this method we determine the Poisson's ratio of hydrogel particles composed of polyethylene glycol (PEG) and varying solvents fabricated using a lithography technique. The results demonstrate with high precision the dependence of the hydrogel compressibility on the solvent fraction and character. The method, easy to implement, can be adapted for the measurement of a variety of soft and biological materials.
- arXiv:2003.06230 [pdf]
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Title: (Super)Spreading and drying of trisiloxane-laden quantum dot nanofluids on hydrophobic surfacesComments: 21 pages, 11 figuresSubjects: Soft Condensed Matter (cond-mat.soft); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Fluid Dynamics (physics.flu-dyn)
Nanofluids hold promise for a wide range of areas of industry. However, understanding of wetting behavior and deposition formation in course of drying and spreading of nanofluids, particularly containing surfactants, is still poor. In this paper, the evaporation dynamics of quantum dot-based nanofluids and evaporation-driven self-assembly in nanocolloidal suspensions on hexamethyldisilazane-, polystyrene-, and polypropylene-coated hydrophobic surfaces have been studied experimentally. Moreover, for the very first time, we make a step to understanding of wetting dynamics of superspreader surfactant-laden nanofluids. It was revealed that drying of surfactant-free quantum dot nanofluids in contrast to pure liquids undergoes not three but four evaporation modes including last additional pinning mode when contact angle decreases whilst triple contact line is pinned by the nanocrystals. In contrast to previous studies, it was found out that addition of nanoparticles to aqueous surfactant solutions leads to deterioration of spreading rate and to formation of double coffee ring. For all surfaces examined, superspreading in presence and absence of quantum dot nanoparticles takes place. Despite the formation of coffee rings on all substrates, they have different morphology. Particularly, the knot-like structures are incorporated into the ring on hexamethyldisilazane- and polystyrene-coated surfaces
- arXiv:2003.06231 [pdf, other]
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Title: Pitch-rotational manipulation of single cells and particles using single-beam thermo-optical tweezersAuthors: Sumeet Kumar, M. Gunaseelan, Rahul Vaippully, Amrendra Kumar, Mithun Ajith, Gaurav Vaidya, Soumya Dutta, Basudev RoySubjects: Soft Condensed Matter (cond-mat.soft); Optics (physics.optics)
3D pitch rotation of microparticles and cells assumes importance in a wide variety of applications in biology, physics, chemistry and medicine. Applications such as cell imaging and injection benefit from pitch-rotational manipulation. Generation of such motion in single beam optical tweezers has remained elusive due to complicacies of generating high enough ellipticity perpendicular to the direction of propagation. Further, trapping an extended object at two locations can only generate partial pitch motion by moving one of the foci in the axial direction. Here, we use hexagonal-shaped upconverting particles and single cells trapped close to a gold-coated glass cover slip in a sample chamber to generate complete 360 degree and continuous pitch motion even with a single optical tweezers beam. The tweezers beam passing through the gold surface is partially absorbed and generates a hot-spot to produce circulatory convective flows in the vicinity which rotates the objects. The rotation rate can be controlled by the intensity of the laser light and the thickness of the gold layer. Thus such a simple configuration can turn the particle in the pitch sense. The circulatory flows in this technique have a diameter of about 5 $\mu$m which is smaller than those reported using acousto-fluidic techniques.
- arXiv:2003.06236 [pdf, other]
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Title: Confinement-mediated phase behavior of hydrocarbon fluids: Insights from Monte Carlo simulationsSubjects: Soft Condensed Matter (cond-mat.soft); Computational Physics (physics.comp-ph)
The phase behavior of hydrocarbon fluids confined in porous media has been reported to deviate significantly from that in the bulk environment due to the existence of sub-10nm pores. Though experiments and simulations have measured the bubble/dew points and sorption isotherms of hydrocarbons confined in both natural and synthetic nanopores, the confinement effects in terms of the strength of fluid-pore interactions tuned by surface wettability and chemistry have received comparably less discussion. More importantly, the underlying physics of confinement-induced phenomena remain obfuscated. In this work, we studied the phase behavior and capillary condensation of n-hexane to understand the effects of confinement at the molecular level. To systematically investigate the pore effects, we constructed two types of wall confinements; one is a structureless virtual wall described by the Steele potential and the other one is an all-atom amorphous silica structure with surface modified by hydroxyl groups. Our numerical results demonstrated the importance of fluid-pore interaction, pore size, and pore morphology effects in mediating the pressure-volume-temperature (PVT) properties of hydrocarbons. The most remarkable finding of this work was that the saturation pressure predicted from the van der Waals-type adsorption isothermal loop could be elevated or suppressed relative to the bulk phase, as illustrated in the graphical abstract. As the surface energy (i.e., fluid-pore interaction) decreased, the isothermal vapor pressure increased, indicating a greater preference for the fluid to exist in the vapor state. Sufficient reduction of the fluid-pore interactions could even elevate the vapor pressure above that of the bulk fluid.
- arXiv:2003.06237 [pdf, ps, other]
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Title: Self-Induced Rayleigh-Taylor Instability in Segregating Dry Granular FlowsJournal-ref: Phys. Rev. Lett. 124, 178001 (2020)Subjects: Soft Condensed Matter (cond-mat.soft); Classical Physics (physics.class-ph); Geophysics (physics.geo-ph)
Dry granular material flowing on rough inclines can experience a self-induced Rayleigh-Taylor (RT) instability followed by the spontaneous emergence of convection cells. For this to happen, particles are different in size and density, the larger particles are the denser but still segregate toward the surface. When the flow is, as usual, initially made of two layers, dense particles above, a Rayleigh-Taylor instability develops during the flow. When the flow is initially made of one homogeneous layer mixture, the granular segregation leads to the formation of an unstable layer of large-dense particles at the surface which subsequently destabilizes in a RT plume pattern. The unstable density gradient has been only induced by the motion of the granular matter. This self-induced Rayleigh-Taylor instability and the two-layer RT instability are studied using two different methods, experiments and simulations. At last, contrarily to the usual fluid behavior where the RT instability relaxes into two superimposed stable layers of fluid, the granular flow evolves to a pattern of alternated bands corresponing to recirculation cells analogous to Rayleigh-B{\'e}nard convection cells where segregation sustains the convective motion.
- arXiv:2003.06239 [pdf, other]
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Title: Unjamming of active rotatorsAuthors: Linda Ravazzano, Maria Chiara Lionetti, Maria Rita Fumagalli, Silvia Bonfanti, Roberto Guerra, Oleksandr Chepizhko, Caterina A. M. La Porta, Stefano ZapperiComments: 18 pages, 5 figuresSubjects: Soft Condensed Matter (cond-mat.soft); Biological Physics (physics.bio-ph)
Active particle assemblies can exhibit a wide range of interesting dynamical phases depending on internal parameters such as density, adhesion strength or self-propulsion. Active self-rotations are rarely studied in this context, although they can be relevant for active matter systems, as we illustrate by analyzing the motion of Chlamydomonas reinhardtii algae under different experimental conditions. Inspired by this example, we simulate the dynamics of a system of interacting active disks endowed with active torques. At low packing fractions, adhesion causes the formation of small rotating clusters, resembling those observed when algae are stressed. At higher densities, the model shows a jamming to unjamming transition promoted by active torques and hindered by adhesion. Our results yield a comprehensive picture of the dynamics of active rotators, providing useful guidance to interpret experimental results in cellular systems where rotations might play a role.
- arXiv:2003.06247 [pdf, other]
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Title: Polaritonic normal modes in Transition State TheoryComments: 5 pages, 2 figuresSubjects: Chemical Physics (physics.chem-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
A series of experiments demonstrate that strong light-matter coupling between vibrational excitations in isotropic solutions of molecules and resonant infrared optical microcavity modes leads to modified thermally-activated kinetics. However, Feist and coworkers [\emph{Phys. Rev. X.}, \textbf{9}, 021057(2019)] have recently demonstrated that, within transition state theory, the effects of strong light-matter coupling with reactive modes are electrostatic and essentially independent of light-matter resonance or even of the formation of vibrational polaritons. To analyze this puzzling theoretical result in further detail, we revisit it under a new light, invoking a normal mode analysis of the transition state and reactant configurations for an ensemble of an arbitrary number of molecules in a cavity, obtaining simple analytical expressions that produce similar conclusions as Feist. While these effects become relevant in optical microcavities if the molecular dipoles are anisotropically aligned, or in cavities with extreme confinement of the photon modes, they become negligible for isotropic solutions in microcavities. It is concluded that further studies are necessary to track the origin of the experimentally observed kinetics.
- arXiv:2003.06257 [pdf]
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Title: Mo Thio and Oxo-Thio Molecular Complexes Film as Self-Healing Catalyst for Photocatalytic Hydrogen Evolution on 2D MaterialsAuthors: Juliana Barros Barbosa, Pierre Louis Taberna, Valerie Bourdon, Iann C. Gerber, Romuald Poteau, Andrea Balocchi, Xavier Marie, Jerome Esvan, Pascal Puech, Antoine Barnabé, Lucianna Da Gama Fernandes Vieira, Ionut-Tudor Moraru, Jean Yves Chane-ChingSubjects: Applied Physics (physics.app-ph); Materials Science (cond-mat.mtrl-sci)
2D semiconducting nanosheets of Transition Metal Dichalcogenides are attractive materials for solar energy conversion because of their unique absorption properties. Here, we propose Mo thio- and oxo-thio-complexes anchored on 2D p-WSe2 nanosheets for efficient water splitting under visible light irradiation with photocurrent density up to 2.0 mA cm-2 at -0.2 V/NHE. Besides developing high electro-catalytic activity, the Mo complexe films were shown to display ability to heal surface defects. We propose that the observed healing of surface defects arises from the strong adsorption on point defects of the 2D WSe2 substrate of Mo complexes such as (MoS4)2-, (MoOS3)2-, (Mo2S6O2)2- as shown from DFT calculations. In addition to display catalytic and healing effects, the thio-, oxo-thio Mo complexes films were shown to enhance charge carrier separation and migration for the hydrogen evolution reaction, thus representing an example of multicomponent passivation layer exhibiting multiple properties.
- arXiv:2003.06295 [pdf, other]
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Title: Experimental demonstration and analysis of random field effects in ferromagnet/antiferromagnet bilayersComments: funding information and a few typos correctedJournal-ref: Phys. Rev. B 101, 144427 (2020)Subjects: Materials Science (cond-mat.mtrl-sci); Disordered Systems and Neural Networks (cond-mat.dis-nn); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
More than 30 years ago, Malozemoff (Phys. Rev. B 35, 3679 (1987)) hypothesized that exchange interaction at the interface between a ferromagnet (F) and an antiferromagnet (AF) can act as an effective random field, which can profoundly affect the magnetic properties of the system. However, until now this hypothesis has not been directly experimentally tested. We utilize magnetoelectronic measurements to analyze the effective exchange fields at Permalloy/CoO interface. Our results cannot be explained in terms of quasi-uniform effective exchange fields, but are in agreement with the random-field hypothesis of Malozemoff. The presented approach opens a new route for the quantitative analysis of effective exchange fields and anisotropies in magnetic heterostructures for memory, sensing and computing applications.
- arXiv:2003.06305 [pdf, other]
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Title: Effect of zitterbewegung on the propagation of wave packets in ABC-stacked multilayer grapheneAuthors: I. R. Lavor, D. R. da Costa, Andrey Chaves, S. H. R. Sena, G. A. Farias, B. Van Duppen, F. M. PeetersComments: Submitted to PRB on February 3rdSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
The time evolution of a low-energy two-dimensional Gaussian wave packet in ABC-stacked $n$-layer graphene (ABC-NLG) is investigated. Expectation values of the position $(x,y)$ of center-of-mass and the total probability densities of the wave packet are calculated analytically using the Green's function method. These results are confirmed using an alternative numerical method based on the split-operator technique within the Dirac approach for ABC-NLG, which additionally allows to include external fields and potentials. The main features of the zitterbewegung (trembling motion) of wave packets in graphene are demonstrated and are found to depend not only on the wave packet width and initial pseudospin polarization, but also on the number of layers. Moreover, the analytical and numerical methods proposed here allow to investigate wave packet dynamics in graphene systems with arbitrary number of layers and arbitrary potential landscapes.
- arXiv:2003.06313 [pdf, other]
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Title: AC Josephson effect between two superfluid time crystalsAuthors: Samuli Autti, Petri J. Heikkinen, Jere T. Mäkinen, Grigori E. Volovik, Vladislav V. Zavjalov, Vladimir B. EltsovComments: 7 pages, 2 figuresSubjects: Other Condensed Matter (cond-mat.other); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Quantum time crystals are systems characterised by spontaneously emerging periodic order in the time domain. A range of such phases has been reported. The concept has even been discussed in popular literature, and deservedly so: while the first speculation on a phase of broken time translation symmetry did not use the name "time crystal", it was later adopted from 1980's popular culture. For the physics community, however, the ultimate qualification of a new concept is its ability to provide predictions and insight. Confirming that time crystals manifest the basic dynamics of quantum mechanics is a necessary step in that direction. We study two adjacent quantum time crystals experimentally. The time crystals, realised by two magnon condensates in superfluid $^3$He-B, exchange magnons leading to opposite-phase oscillations in their populations -- AC Josephson effect -- while the defining periodic motion remains phase coherent throughout the experiment.
- arXiv:2003.06334 [pdf, ps, other]
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Title: Broken symmetry $G_0W_0$ approach for the evaluation of exchange coupling constantsSubjects: Strongly Correlated Electrons (cond-mat.str-el); Chemical Physics (physics.chem-ph)
The applicability of a broken symmetry version of the $G_0W_0$ approximation to the calculation of isotropic exchange coupling constants has been studied. Using a simple H--He--H model system the results show a significant and consistent improvement of the results over both broken symmetry Hartree--Fock and broken symmetry density functional theory. In the case of more realistic bimetallic Cu(II) complexes, inclusion of the $G_0W_0$ correction does not lead to obvious improvement in the results. The discrepancies are explained by improved description of the interactions within the magnetic orbital space upon inclusion of the $G_0W_0$ corrections but deterioration of the description of charge- and spin-polarization effects outside the magnetic orbital space. Overall the results show that computational methods based on the $GW$ method have a potential to improve computational estimates of exchange coupling constants.
- arXiv:2003.06339 [pdf, other]
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Title: Extreme boundary conditions and random tilingsAuthors: Jean-Marie StéphanComments: Expanded version of the lectures given at the SFT-Paris-2019 school on 'Statistical and Condensed Matter Field Theory'. 62 pagesSubjects: Statistical Mechanics (cond-mat.stat-mech); Mathematical Physics (math-ph)
Standard statistical mechanical or condensed matter arguments tell us that bulk properties of a physical system do not depend too much on boundary conditions. Random tilings of large regions provide counterexamples to such intuition, as illustrated by the famous 'arctic circle theorem' for dimer coverings in two dimensions. In these notes, I discuss such examples in the context of critical phenomena, and their relation to 1+1d quantum particle models. All those turn out to share a common feature: they are inhomogeneous, in the sense that local densities now depend on position in the bulk. I explain how such problems may be understood using variational (or hydrodynamic) arguments, how to treat long range correlations, and how non trivial edge behavior can occur. While all this is done on the example of the dimer model, the results presented here have much greater generality. In that sense the dimer model serves as an opportunity to discuss broader methods and results. [These notes require only a basic knowledge of statistical mechanics.]
- arXiv:2003.06358 [pdf]
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Title: Structural, magnetic and insulator-to-metal transitions under pressure in the GaV4S8 Mott insulator: A rich phase diagram up to 14.7 GPaAuthors: Julia Mokdad, Georg Knebel, Christophe Marin, Jean-Pascal Brison, Vinh Ta Phuoc, Rodolphe Sopracase, Claire Colin, Daniel BraithwaiteComments: 8 pages, 9 figuresJournal-ref: Phys. Rev. B 100, 245101 (2019)Subjects: Strongly Correlated Electrons (cond-mat.str-el)
In addition to its promising potential for applications, GaV4S8 shows very interesting physical properties with temperature and magnetic field. These properties can be tuned by applying hydrostatic pressure in order to reveal and understand the physics of these materials. Not only pressure induces an insulator-to-metal transition in GaV4S8 but it also has an interesting effect on the structural and magnetic transitions. Using a combination of AC calorimetry, capacitance, and resistivity measurements under pressure, we determine the evolution of the structural and magnetic transitions with pressure and thus establish the T-P phase diagram of GaV4S8. To detect the insulator-to-metal transition, we use optical conductivity and DC resistivity measurements and we follow the evolution of the Mott gap under pressure. The structural transition temperature increases with pressure and a second transition appears above 6 GPa indicating a possible new phase with a very small gap. Pressure has surprisingly a very weak effect on the ferromagnetic transition that persists even very close to the IMT that occurs at around 14 GPa, implying that the metallic state may also be magnetic.
- arXiv:2003.06364 [pdf, ps, other]
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Title: Kinetics of random sequential adsorption of two-dimensional shapes on a one-dimensional lineComments: 7 pages, 10 figuresSubjects: Statistical Mechanics (cond-mat.stat-mech)
Saturated random sequential adsorption packings built of two-dimensional ellipses, spherocylinders, rectangles, and dimers placed on a one-dimensional line are studied to check analytical prediction concerning packing growth kinetics [A. Baule, Phys. Rev. Let. 119, 028003 (2017)]. The results show that the kinetics is governed by the power-law with the exponent $d=1.5$ and $2.0$ for packings built of ellipses and rectangles, respectively, which is consistent with analytical predictions. However, for spherocylinders and dimers of moderate width-to-height ratio, a transition between these two values is observed. We argue that this transition is a finite size effect that arises for spherocylinders due to the properties of the contact function. In general, it appears that the kinetics of packing growth can depend on packing size even for very large packings.
- arXiv:2003.06372 [pdf, ps, other]
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Title: Transition between anomalous and Anderson localization in systems with non-diagonal disorder driven by time-periodic fieldsComments: 10 pages, 4 figuresSubjects: Disordered Systems and Neural Networks (cond-mat.dis-nn); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Quantum Physics (quant-ph)
In models of hopping disorder in the absence of external fields and at the band center, the electrons are less localized in space than the standard exponential Anderson localization. A signature of this anomalous localization is the square root dependence of the logarithmic average of the conductance on the system length, in contrast to the linear length dependence for Anderson localized systems. We study the effect of a time-periodic external field in the scaling and distribution of the conductance of a quantum wire with hopping disorder. In the low-frequency regime, we show a transition between anomalous localization and Anderson localization as a function of the parameters of the external field. The Floquet modes mix different energy contributions and standard length dependence of the logarithmic average of the conductance is gradually recovered as we lower the frequency or increase the amplitude of the external field. In the high-frequency regime, the system presents still anomalous localization but the conductance is also renormalized, depending on the parameters of the external field, by interference effects at the coupling to the leads. This allows for a high degree of control of the average of the conductance.
- arXiv:2003.06385 [pdf, other]
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Title: Nonreciprocal Second-Harmonic Generation in Few-Layer Chromium TriiodideComments: 8 pages and 8 figuresSubjects: Materials Science (cond-mat.mtrl-sci); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Computational Physics (physics.comp-ph); Optics (physics.optics)
It is of fundamental importance but challenging to simultaneously identify atomic and magnetic configurations of two-dimensional van der Waals materials. In this work, we show that the nonreciprocal second-harmonic generation (SHG) can be a powerful tool to answer this challenge. Despite the preserved lattice inversion symmetry, the interlayer antiferromagnetic order and spin-orbit coupling generate enhanced SHG in PT-symmetric bilayer chromium triiodide (CrI3). Importantly, the in-plane polarization-resolved SHG is sensitive to subtly different interlayer structures that cannot be told by linear optical spectra. Beyond bilayer, we further predict that the intensity and angle-resolved SHG can be employed to identify both interlayer atomic and magnetic configurations of trilayer CrI3. Our first-principles results agree with available measurements and show the potential of SHG as a non-contacting approach to explore correlations between interlayer structures and magnetic orders of emerging ultra-thin magnetic materials.
- arXiv:2003.06393 [pdf, other]
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Title: Enhanced antiferromagnetic ordering tendency in staggered periodic Anderson modelAuthors: Mi JiangComments: To appear in PRB. This work is extended in arXiv:2004.11781 with some text overlapSubjects: Strongly Correlated Electrons (cond-mat.str-el)
Heavy fermion compounds consisting of two or more inequivalent local moment sites per unit cell have been a promising platform of investigating the interplay between distinct Kondo screenings that is absent in the conventional systems containing only one rare-earth ion per unit cell. We report a remarkable enhancement of the antiferromagnetic (AF) ordering tendency in the staggered periodic Anderson model (PAM) with two alternating inequivalent local moments if their hybridization strengths reside in the Kondo singlet and antiferromagnetic insulator regime separately of the phase diagram of homogeneous PAM. Our results uncover the rich physics induced by the interplay of multiple energy scales in the staggered PAM and furthermore implies the ubiquitous existence of the enhancement of physical quantities in general inhomogeneous systems.
- arXiv:2003.06395 [pdf, other]
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Title: Semiclassical Approximation meets Keldysh-Schwinger diagrammatic technique: Scalar $\varphi^4$Comments: 16 pages, many diagramsSubjects: High Energy Physics - Phenomenology (hep-ph); Statistical Mechanics (cond-mat.stat-mech); High Energy Physics - Theory (hep-th); Nuclear Theory (nucl-th)
We study the evolution of the non-equilibrium quantum fields from a highly excited initial state in two approaches: the standard Keldysh-Schwinger diagram technique and the semiclassical expansion. We demonstrate explicitly that these two approaches coincide if the coupling constant $g$ and the Plank constant $\hbar$ are small simultaneously. Also, we discuss loop diagrams of the perturbative approach, which are summed up by the leading order term of the semiclassical expansion. As an example, we consider shear viscosity for the scalar field theory at the leading semiclassical order. We introduce the new technique that unifies both semiclassical and diagrammatic approaches and open the possibility to perform the resummation of the semiclassical contributions.
- arXiv:2003.06401 [pdf, other]
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Title: Mobile orbitons in Ca$_2$CuO$_3$: crucial role of the Hund's exchangeAuthors: Roberto Fumagalli, Jonas Heverhagen, Davide Betto, Riccardo Arpaia, Matteo Rossi, Daniele Di Castro, Nicholas B. Brookes, Marco Moretti Sala, Maria Daghofer, Lucio Braicovich, Krzysztof Wohlfeld, Giacomo GhiringhelliComments: 13 pages, 10 figuresJournal-ref: Phys. Rev. B 101, 205117 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el); Superconductivity (cond-mat.supr-con)
We investigate the Cu $L_3$ edge resonant inelastic x-ray scattering (RIXS) spectra of a quasi-1D antiferromagnet Ca$_2$CuO$_3$. In addition to the magnetic excitations, which are well-described by the two-spinon continuum, we observe two dispersive orbital excitations, the $3d_{xy}$ and the $3d_{yz}$ orbitons. We carry out a quantitative comparison of the RIXS spectra, obtained with two distinct incident polarizations, with a theoretical model. We show that any realistic spin-orbital model needs to include a finite, but realistic, Hund's exchange $J_H \approx 0.5$ eV. Its main effect is an increase in orbiton velocities, so that their theoretically calculated values match those observed experimentally. Even though Hund's exchange also mediates some interaction between spinon and orbiton, the picture of spin-orbit separation remains intact and describes orbiton motion in this compound.
- arXiv:2003.06408 [pdf, other]
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Title: Persistent Currents in Toroidal Dipolar SupersolidsSubjects: Quantum Gases (cond-mat.quant-gas)
We investigate the rotational properties of a dipolar Bose-Einstein condensate trapped in a toroidal geometry. Studying the ground states in the rotating frame and at fixed angular momenta, we observe that the condensate acts in distinctly different ways depending on whether it is in the superfluid or in the supersolid phase. We find that intriguingly, the toroidal dipolar condensate can support a supersolid persistent current which occurs at a local minimum in the ground state energy as a function of angular momentum, where the state has a vortex solution in the superfluid component of the condensate. The decay of this state is prevented by a barrier that in part consists of states where a fraction of the condensate mimics solid-body rotation in a direction opposite to that of the vortex. Furthermore, the rotating toroidal supersolid shows hysteretic behavior that is qualitatively different depending on the superfluid fraction of the condensate.
- arXiv:2003.06413 [pdf, other]
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Title: Equivariant flow-based sampling for lattice gauge theoryAuthors: Gurtej Kanwar, Michael S. Albergo, Denis Boyda, Kyle Cranmer, Daniel C. Hackett, Sébastien Racanière, Danilo Jimenez Rezende, Phiala E. ShanahanComments: 6 pages, 4 figuresSubjects: High Energy Physics - Lattice (hep-lat); Statistical Mechanics (cond-mat.stat-mech); Machine Learning (cs.LG)
We define a class of machine-learned flow-based sampling algorithms for lattice gauge theories that are gauge-invariant by construction. We demonstrate the application of this framework to U(1) gauge theory in two spacetime dimensions, and find that near critical points in parameter space the approach is orders of magnitude more efficient at sampling topological quantities than more traditional sampling procedures such as Hybrid Monte Carlo and Heat Bath.
- arXiv:2003.06414 [pdf, other]
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Title: Non-Newtonian flow effects in supercooled waterJournal-ref: Phys. Rev. Research 2, 022004 (2020)Subjects: Soft Condensed Matter (cond-mat.soft); Other Condensed Matter (cond-mat.other); Computational Physics (physics.comp-ph)
The viscosity of supercooled water has been a subject of intense study, in particular with respect to its temperature dependence. Much less is known, however, about the influence of dynamical effects on the viscosity in its supercooled state. Here we address this issue for the first time, using molecular dynamics simulations to investigate the shear-rate dependence of the viscosity of supercooled water as described by the TIP4P/Ice model. We show the existence of a distinct cross-over from Newtonian to non-Newtonian behavior characterized by a power-law shear-thinning regime. The viscosity reduction is due to the decrease in the connectivity of the hydrogen-bond network. Moreover, the shear thinning intensifies as the degree of supercooling increases, whereas the cross-over flow rate is approximately inversely proportional to the Newtonian viscosity. These results stimulate further investigation into possible fundamental relations between these nonequilibrium effects and the quasi-static Newtonian viscosity behavior of supercooled water.
Replacements
- arXiv:1703.09834 (replaced) [pdf, other]
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Title: Persistent Currents in Ferromagnetic CondensatesAuthors: Austen LamacraftComments: 10 pages, 7 figures. Accepted versionJournal-ref: Phys. Rev. B 95, 224512 (2017)Subjects: Quantum Gases (cond-mat.quant-gas)
Persistent currents in Bose condensates with a scalar order parameter are stabilized by the topology of the order parameter manifold. In condensates with multicomponent order parameters it is topologically possible for supercurrents to `unwind' without leaving the manifold. We study the energetics of this process in the case of ferromagnetic condensates using a long wavelength energy functional that includes both the superfluid and spin stiffnesses. Exploiting analogies to an elastic rod and rigid body motion, we show that the current carrying state in a 1D ring geometry transitions between a spin helix in the energy minima and a soliton-like configuration at the maxima. The relevance to recent experiments in ultracold atoms is briefly discussed.
- arXiv:1711.06991 (replaced) [pdf, ps, other]
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Title: Order, disorder and phase transitions in quantum many body systemsAuthors: Alessandro GiulianiComments: 35 pages, 7 figures. These notes are based on a presentation given at the Istituto Lombardo, Accademia di Scienze e Lettere, in Milano (Italy) on May 5, 2016, as well as on the notes of a course given at the EMS-IAMP summer school in mathematical physics `Universality, Scaling Limits and Effective Theories', held in Roma (Italy) on July 11-15, 2016. Final version, accepted for publicationJournal-ref: Istituto Lombardo (Rend. Scienze) 150, 3-46 (2016)Subjects: Statistical Mechanics (cond-mat.stat-mech); Mathematical Physics (math-ph)
In this paper, I give an overview of some selected results in quantum many body theory, lying at the interface between mathematical quantum statistical mechanics and condensed matter theory. In particular, I discuss some recent results on the universality of transport coefficients in lattice models of interacting electrons, with specific focus on the independence of the quantum Hall conductivity from the electron-electron interaction. In this context, the exchange of ideas between mathematical and theoretical physics proved particularly fruitful, and helped in clarifying the role played by quantum conservation laws (Ward Identities), together with the decay properties of the Euclidean current-current correlation functions, on the interaction-independence of the conductivity.
- arXiv:1803.10083 (replaced) [pdf, ps, other]
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Title: Emergence of Cooperation in the thermodynamic limitComments: 21 pages, 4 figures, Accepted for publication in Chaos, Solitons and Fractals (2020)Journal-ref: Chaos, Solitons and Fractals 135, 109762 (2020)Subjects: Physics and Society (physics.soc-ph); Statistical Mechanics (cond-mat.stat-mech); Computer Science and Game Theory (cs.GT); Econometrics (econ.EM); Mathematical Physics (math-ph); Populations and Evolution (q-bio.PE)
Predicting how cooperative behavior arises in the thermodynamic limit is one of the outstanding problems in evolutionary game theory. For two player games, cooperation is seldom the Nash equilibrium. However, in the thermodynamic limit cooperation is the natural recourse regardless of whether we are dealing with humans or animals. In this work, we use the analogy with the Ising model to predict how cooperation arises in the thermodynamic limit.
- arXiv:1806.01723 (replaced) [pdf, other]
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Title: Noisy Coupled Qubits: Operator Spreading and the Fredrickson-Andersen ModelComments: 11 pages, 7 figures. Accepted versionJournal-ref: Phys. Rev. B 98, 195125 (2018)Subjects: Statistical Mechanics (cond-mat.stat-mech); Quantum Physics (quant-ph)
We study noise-averaged observables for a system of exchange-coupled quantum spins (qubits), each subject to a stochastic drive, by establishing mappings onto stochastic models in the strong-noise limit. Averaging over noise yields Lindbladian equations of motion; when these are subjected to a strong-noise perturbative treatment, classical master equations are found to emerge. The dynamics of noise averages of operators displays diffusive behaviour or exponential relaxation, depending on whether the drive conserves one of the spin components or not. In the latter case, the second moment of operators -- from which the average subsystem purity and out-of-time-order correlation functions can be extracted -- is described by the Fredrickson-Andersen model, originally introduced as a model of cooperative relaxation near the glass transition. It is known that fluctuations of a ballistically propagating front in the model are asymptotically Gaussian in one dimension. We extend this by conjecturing, with strong numerical evidence, that in two dimensions the long-time fluctuations are in the Kardar-Parisi-Zhang universality class, complementing a similar observation in random unitary circuits.
- arXiv:1811.08421 (replaced) [pdf, other]
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Title: Trends of information backflow in disordered spin chainsComments: 7 pages, 4 figures, close to the published versionJournal-ref: Euro Physics Letters, 129, 30005 (2020)Subjects: Quantum Physics (quant-ph); Disordered Systems and Neural Networks (cond-mat.dis-nn); Strongly Correlated Electrons (cond-mat.str-el)
We investigate the trends of information backflow associated with the dynamics of a sub-part of a disordered spin-1/2 transverse field Heisenberg chain for different regimes of the Hamiltonian. Towards this aim, the decay profile of bipartite entanglement shared between a probe-qubit and a system-qubit (sub-part) of the chain is monitored in time. A clear shift in the trends of the decay profiles of the bipartite entanglement from monotonic in the low-disorder limit to non-monotonic in the moderately large disorder limit occurs due to strong information backflow from the environment (complementary-part) to the system-qubit. A connection between environmental interruption caused by the information backflow and the disorder strength is established by examining the entanglement revival frequencies. The growth patterns of the revival frequencies in the localized phase play an instrumental role to effectively distinguish an interacting system (many-body localized) from its non-interacting (Anderson localized) counterpart.
- arXiv:1903.02067 (replaced) [pdf, other]
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Title: An investigation of pre-crystalline order, ruling out Pauli crystals and introducing Pauli anti-crystalsComments: 17 pages, 8 figures; v2 Title changeJournal-ref: Sci Rep 10, 3710 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el)
Fluid states of matter can locally exhibit characteristics of the onset of crystalline order. Traditionally this has been theoretically investigated using multipoint correlation functions. However new measurement techniques now allow multiparticle configurations of cold atomic systems to be observed directly. This has led to a search for new techniques to characterize the configurations that are likely to be observed. One of these techniques is the configuration density (CD), which has been used to argue for the formation of "Pauli crystals" by non-interacting electrons in e.g. a harmonic trap. We show here that such Pauli crystals do not exist, but that other other interesting spatial structures can occur in the form of an "anti-Crystal", where the fermions preferentially avoid a lattice of positions surrounding any given fermion. Further, we show that configuration densities must be treated with great care as naive application can lead to the identification of crystalline structures which are artifacts of the method and of no physical significance. We analyze the failure of the CD and suggest methods that might be more suitable for characterizing multiparticle correlations which may signal the onset of crystalline order. In particular, we introduce neighbour counting statistics (NCS), which is the full counting statistics of the particle number in a neighborhood of a given particle. We test this on two dimensional systems with emerging triangular and square crystal structures.
- arXiv:1905.10640 (replaced) [pdf, other]
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Title: Modeling work-speed-accuracy trade-offs in a stochastic rotary machineComments: 7 pages, 4 figuresJournal-ref: Phys. Rev. E 101, 032110 (2020)Subjects: Statistical Mechanics (cond-mat.stat-mech); Biological Physics (physics.bio-ph)
Molecular machines are stochastic systems that catalyze the energetic processes keeping living cells alive and structured. Inspired by the examples of F1-ATP synthase and the bacterial flagellum, we present a minimal model of an externally driven stochastic rotary machine. We explore the trade-offs of work, driving speed, and driving accuracy when changing driving strength, speed, and the underlying system dynamics. We find an upper bound on accuracy and work for a particular speed. Our results favor slow driving when tasked with minimizing the work-accuracy ratio and maximizing the rate of successful cycles. Finally, in the parameter regime mapping to the dynamics of F1-ATP synthase, we find a significant decay of driving accuracy at physiological rotation rates, raising questions about how ATP synthase achieves reasonable or even remarkable efficiency in vivo.
- arXiv:1906.02637 (replaced) [pdf, ps, other]
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Title: Quantum quench in PT-symmetric Luttinger liquidComments: 6+1 pages, 3 figuresJournal-ref: Phys. Rev. Lett. 124, 136802 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el); Quantum Gases (cond-mat.quant-gas)
A Luttinger liquid (LL) describes low energy excitations of many interacting one dimensional systems, and exhibits universal response both in and out of equilibrium. We analyze its behaviour in the non-hermitian realm after quantum quenching to a PT-symmetric LL by focusing on the fermionic single particle density matrix. For short times, we demonstrate the emergence of unique phenomena, characteristic to non-hermitian systems, that correlations propagate faster than the conventional maximal speed, known as the Lieb-Robinson bound. These emergent supersonic modes travel with velocities that are multiples of the conventional light-cone velocity. This behaviour is argued to be generic for correlators in non-hermitian systems. In the long time limit, we find typical LL behaviour, extending the LL universality to the non-equilibrium non-hermitian case. Our analytical results are benchmarked numerically and indicate that the dispersal of quantum information is much faster in non-hermitian systems.
- arXiv:1907.04464 (replaced) [pdf, ps, other]
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Title: The stability phase diagram of active Brownian particlesAuthors: Pin Nie, Joyjit Chattoraj, Antonio Piscitelli, Patrick Doyle, Ran Ni, Massimo Pica CiamarraComments: Physical Review Research, to appear. In the revised manuscript, the theoretical model is validated against simulations spanning a larger range of parametersJournal-ref: Phys. Rev. Research 2, 023010 (2020)Subjects: Soft Condensed Matter (cond-mat.soft); Statistical Mechanics (cond-mat.stat-mech)
Phase separation in a low-density gas-like phase and a high-density liquid-like one is a common trait of biological and synthetic self-propelling particles' systems. The competition between motility and stochastic forces is assumed to fix the boundary between the homogeneous and the phase-separated phase. Here we demonstrate that motility does also promote the homogeneous phase allowing particles to resolve their collisions. This new understanding allows quantitatively predicting the spinodal-line of hard self-propelling Brownian particles, the prototypical model exhibiting a motility induced phase separation. Furthermore, we demonstrate that frictional forces control the physical process by which motility promotes the homogeneous phase. Hence, friction emerges as an experimentally variable parameter to control the motility induced phase diagram.
- arXiv:1907.05354 (replaced) [pdf, other]
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Title: Interplay of topology and electron-electron interactions in Rarita-Schwinger-Weyl semimetalsAuthors: Igor BoettcherComments: 4+ pages and supplemental material, published versionJournal-ref: Phys. Rev. Lett. 124, 127602 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el); Superconductivity (cond-mat.supr-con); High Energy Physics - Theory (hep-th)
We study for the first time the effects of strong short-range electron-electron interactions in generic Rarita--Schwinger--Weyl semimetals hosting spin-3/2 electrons with linear dispersion at a four-fold band crossing point. The emergence of this novel quasiparticle, which is absent in high-energy physics, has recently been confirmed experimentally in the solid state. We combine symmetry considerations and a perturbative renormalization group analysis to discern three interacting phases that are prone to emerge in the strongly correlated regime: The chiral topological semimetal breaks a $\mathbb{Z}_2$-symmetry and features four Weyl nodes of monopole charge +1 located at vertices of a tetrahedron in momentum space. The s-wave superconducting state opens a Majorana mass gap for the fermions and is the leading superconducting instability. The Weyl semimetal phase removes the fourfold degeneracy and creates two Weyl nodes with either equal or opposite chirality depending on the anisotropy of the band structure. We find that symmetry breaking occurs at weaker coupling if the total monopole charge remains constant across the transition.
- arXiv:1907.08105 (replaced) [pdf, other]
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Title: The Marginal Stability of the Meta-stable Thouless-Anderson-Palmer StatesAuthors: T.PlefkaComments: 9 Pages, 8 figures, Enlarged version with substantial changes, additional new results and 2 new figuresSubjects: Disordered Systems and Neural Networks (cond-mat.dis-nn); Statistical Mechanics (cond-mat.stat-mech)
The existing investigations on the complexity are extended. In addition to the Edward-Anderson Parameter q_2 the fourth moment q_4 of the magnetizations m_i is included to the set of constrained variables and the constrained complexity is numerically determined. The maximum of the constrained complexity (representing the total complexity) sticks at the boundary for temperatures at and below a new critical temperature. This implies marginal stability. The temperature dependence of lowest value of the Gibbs potential consistent with all requirements is presented.
- arXiv:1907.12231 (replaced) [pdf]
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Title: A Model for Grain Boundary ThermodynamicsAuthors: Reza Darvishi KamachaliComments: 27 pages, 8 figures, original workSubjects: Materials Science (cond-mat.mtrl-sci)
A model is proposed for assessing grain boundary thermodynamics based on available bulk thermodynamic data. A continuous atomic density field and its gradients are introduced to describe the grain boundary region. We derive a density-based Gibbs free energy and compute grain boundary phase diagram. Grain boundary segregation and the coexistence of the bulk and grain boundary phases are discussed. The model is qualitatively demonstrated on the segregation and interfacial phase separation in the Pt-Au system. The relationships between the grain boundary's atomic density, excess free volume, and misorientation angle are discussed. The current density-based model is readily applicable to study phase equilibria in grain boundaries and opens possibilities to develop microstructure design concepts based on segregation engineering.
- arXiv:1908.08723 (replaced) [pdf, other]
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Title: Nonlocal Coulomb interaction and spin-freezing crossover as a route to valence-skipping charge orderJournal-ref: npj Quantum Materials volume 5, Article number: 19 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el)
Multiorbital systems away from global half-filling host intriguing physical properties promoted by Hund's coupling. Despite increasing awareness of this regime dubbed Hund's metal, effect of nonlocal interaction is still elusive. Here we study a three-orbital model with $1/3$ filling (two electrons per site) including the intersite Coulomb interaction ($V$). Using the $GW$ plus extended dynamical mean-field theory, the valence-skipping charge order transition is shown to be driven by $V$. Most interestingly, the instability to this transition is significantly enhanced in the spin-freezing crossover regime, thereby lowering the critical $V$ to the formation of charge order. This behavior is found to be closely related to the population profile of the atomic multiplet states in the spin-freezing regime. In this regime, maximum spin states are dominant in each total charge subspace with substantial amount of one- and three-electron occupations, which leads to almost equal population of one- and the maximum spin three-electron state. Our finding unveils another feature of the Hund's metal, and has potential implications for the broad range of multiorbital systems as well as the recently discovered charge order in iron-pnictides.
- arXiv:1910.00331 (replaced) [pdf, ps, other]
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Title: Active nematics with anisotropic friction: the decisive role of the flow aligning parameterJournal-ref: Soft Matter 16 (2020) 2065--2074Subjects: Soft Condensed Matter (cond-mat.soft)
We use continuum simulations to study the impact of anisotropic hydrodynamic friction on the emergent flows of active nematics. We show that, depending on whether the active particles align with or tumble in their collectively self-induced flows, anisotropic friction can result in markedly different patterns of motion. In a flow-aligning regime and at high anisotropic friction, the otherwise chaotic flows are streamlined into flow lanes with alternating directions, reproducing the experimental laning state that has been obtained by interfacing microtubule-motor protein mixtures with smectic liquid crystals. Within a flow-tumbling regime, however, we find that no such laning state is possible. Instead, the synergistic effects of friction anisotropy and flow tumbling can lead to the emergence of bound pairs of topological defects that align at an angle to the easy flow direction and navigate together throughout the domain. In addition to confirming the mechanism behind the laning states observed in experiments, our findings emphasise the role of the flow aligning parameter in the dynamics of active nematics.
- arXiv:1910.04419 (replaced) [pdf, ps, other]
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Title: Analytical criteria for magnetization reversal in $\varphi_0$ Josephson junctionSubjects: Superconductivity (cond-mat.supr-con)
The $\varphi_0$ Josephson junctions formed by ordinary superconductors and a magnetic non-centrosymmetric interlayer are studied. We derive an analytical solution for the magnetization dynamics induced by an arbitrary current pulse and formulate the criteria for magnetization reversal. Using the obtained results, the form and duration of the current pulse are optimized. The agreement between analytical and numerical investigations is reached in the case of a large product of the ratio Josephson to magnetic energy, strength of spin-orbit interaction and a minimal value of the current pulse. The obtained results allow one to predict magnetization reversal at the chosen system parameters.
- arXiv:1910.05194 (replaced) [pdf, other]
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Title: KITE: high-performance accurate modelling of electronic structure and response functions of large molecules, disordered crystals and heterostructuresAuthors: Simão M. João, Miša Anđelković, Lucian Covaci, Tatiana Rappoport, João M. V. P. Lopes, Aires FerreiraComments: 38 pages, 13 figures, 3 tables. Published versionJournal-ref: R. Soc. open sci. 7, 191809 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci); Computational Physics (physics.comp-ph)
We present KITE, a general purpose open-source tight-binding software for accurate real-space simulations of electronic structure and quantum transport properties of large-scale molecular and condensed systems with tens of billions of atomic orbitals (N~10^10). KITE's core is written in C++, with a versatile Python-based interface, and is fully optimised for shared memory multi-node CPU architectures, thus scalable, efficient and fast. At the core of KITE is a seamless spectral expansion of lattice Green's functions, which enables large-scale calculations of generic target functions with uniform convergence and fine control over energy resolution. Several functionalities are demonstrated, ranging from simulations of local density of states and photo-emission spectroscopy of disordered materials to large-scale computations of optical conductivity tensors and real-space wave-packet propagation in the presence of magneto-static fields and spin-orbit coupling. On-the-fly calculations of real-space Green's functions are carried out with an efficient domain decomposition technique, allowing KITE to achieve nearly ideal linear scaling in its multi-threading performance. Crystalline defects and disorder, including vacancies, adsorbates and charged impurity centers, can be easily set up with KITE's intuitive interface, paving the way to user-friendly large-scale quantum simulations of equilibrium and non-equilibrium properties of molecules, disordered crystals and heterostructures subject to a variety of perturbations and external conditions.
- arXiv:1910.07797 (replaced) [pdf, other]
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Title: On zero-remainder conditions in the Bethe ansatzComments: 14 pages. New version: corrected typos, modified abstract and added referencesJournal-ref: JHEP, article number 178 (2020)Subjects: High Energy Physics - Theory (hep-th); Statistical Mechanics (cond-mat.stat-mech); Mathematical Physics (math-ph)
We prove that physical solutions to the Heisenberg spin chain Bethe ansatz equations are exactly obtained by imposing two zero-remainder conditions. This bridges the gap between different criteria, yielding an alternative proof of a recently devised algorithm based on $QQ$ relations, and solving its minimality issue.
- arXiv:1910.07805 (replaced) [pdf, ps, other]
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Title: On Generalized $Q$-systemsComments: 27 pages. New version: included code, modified sec 3.2, and a few minor changesJournal-ref: JHEP, article number 177 (2020)Subjects: High Energy Physics - Theory (hep-th); Statistical Mechanics (cond-mat.stat-mech); Mathematical Physics (math-ph)
We formulate $Q$-systems for the closed XXZ, open XXX and open quantum-group-invariant XXZ quantum spin chains. Polynomial solutions of these $Q$-systems can be found efficiently, which in turn lead directly to the admissible solutions of the corresponding Bethe ansatz equations.
- arXiv:1910.09023 (replaced) [pdf, ps, other]
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Title: Ultrafast energy absorption and photoexcitation of bulk plasmon in crystalline silicon subjected to intense near-infrared ultrashort laser pulsesJournal-ref: Applied Surface Science 2020Subjects: Optics (physics.optics); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We investigate the non-linear response and energy absorption in bulk silicon irradiated by intense 12-fs near-infrared laser pulses. Depending on the laser intensity, we distinguish two regimes of non-linear absorption of the laser energy: for low intensities, energy deposition and photoionization involve perturbative three-photon transition through the direct bandgap of silicon. For laser intensities near and above 10$^{14}$ W/cm$^2$, corresponding to photocarrier density of order 10$^{22}$ cm$^{-3}$, we find that absorption at near-infrared wavelengths is greatly enhanced due to excitation of bulk plasmon resonance. In this regime, the energy transfer to electrons exceeds a few times the thermal melting threshold of Si. The optical reflectivity of the photoexcited solid is found in good qualitative agreement with existing experimental data. In particular, the model predicts that the main features of the reflectivity curve of photoexcited Si as a function of the laser fluence are determined by the competition between state and band filling associated with Pauli exclusion principle and Drude free-carrier response. The non-linear response of the photoexcited solid is also investigated for irradiation of silicon with a sequence of two strong and temporary non-overlapping pulses. The cumulative effect of the two pulses is non-additive in terms of deposited energy. Photoionization and energy absorption on the leading edge of the second pulse is greatly enhanced due to free carrier absorption.
- arXiv:1911.08043 (replaced) [pdf, other]
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Title: Mapping NP-hard and NP-complete optimisation problems to Quadratic Unconstrained Binary Optimisation problemsAuthors: Bas LodewijksComments: 14 pages, 6 figuresSubjects: Data Structures and Algorithms (cs.DS); Statistical Mechanics (cond-mat.stat-mech); Computational Complexity (cs.CC); Quantum Physics (quant-ph)
We discuss several mappings from well-known NP-hard problems to Quadratic Unconstrained Binary Optimisation problems which are treated incorrectly by Lucas. We provide counterexamples and correct the mappings. We also extend the body of QUBO formulations of NP-complete and NP-hard optimisation problems by discussing additional problems.
- arXiv:1911.12523 (replaced) [pdf, ps, other]
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Title: Weyl superconductor phases in a Weyl-semimetal/superconductor multilayerComments: 11 pages, 8 figuresJournal-ref: Phys. Rev. B 101, 094510 (2020)Subjects: Superconductivity (cond-mat.supr-con)
Topologically nontrivial superconducting phases have been engineered in topological materials by the proximity effect in contact with conventional superconductors. In this paper, by using the method of the Kronig-Penney model, we study the superconducting proximity effect in the bulk electronic states of Weyl semimetals by considering a multilayer structure consisting of Weyl-semimetal and superconductor layers. Due to the proximity effect, two Weyl nodes are decoupled into four nodes of Majorana fermions resulting in Weyl-superconductor phases or three-dimensional extension of topological-superconductor phases. We find that mismatch of the Fermi velocity and potential barriers at the interface gap out Majorana nodes, thus turn Weyl-superconductor phases with four Majorana nodes into Weyl-superconductor phases with half of Majorana nodes and topological-superconductor phases with odd integer Chern numbers.
- arXiv:1911.12620 (replaced) [pdf, ps, other]
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Title: First and Second Order Topological Phases on Ferromagnetic Breathing Kagome LatticeComments: 9 pages, 8 figuresJournal-ref: J. Phys.: Condens. Matter. 32 (2020) 205601Subjects: Strongly Correlated Electrons (cond-mat.str-el)
In this work, topological properties of a ferromagnetic Heisenberg model on a breathing kagome lattice are investigated extensively in the presence of
Dzyaloshinskii-Moriya interaction. While the kagome ferromagnet hosts only a single first order topological phase, the breathing kagome system exhibits multiple first and second order topological phases along with their coexistence. Magnon dispersion relation is obtained by using linear spin wave theory. Flat band and Dirac cones are obtained in the absence of
Dzyaloshinskii-Moriya interaction. A topological phase diagram is presented where several first and second order phases as well as their overlap are identified. Values of thermal Hall conductivity for all the first order phases are obtained. Distinct first order phases are characterized by different sets of Chern numbers in association with the necessary chiral edge states in accordance to the first order bulk-boundary-correspondence rule. Second order phase is characterized by polarization along with the emergence of corner states. Violation of the second order bulk-corner-correspondence rule has been noted in some regions. - arXiv:1912.00599 (replaced) [pdf, other]
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Title: BaHgSn: A Dirac semimetal with surface hourglass fermionsJournal-ref: Phys. Rev. B 101, 115145 (2020)Subjects: Materials Science (cond-mat.mtrl-sci); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We proposed that BaHgSn is a Dirac semimetal (DSM) which can host hourglass-like surface states (HSSs) as protected by nonsymmorphic glide symmetry. Compared to KHgSb, an isostructural topological crystalline insulator with the same HSSs, BaHgSn has an additional band inversion at $\Gamma$ point. This band inversion is induced by the stronger interlayer coupling among Hg-Sn honeycomb layers than that among Hg-Sb-layers in KHgSb, which leads to bulk Dirac nodes in BaHgSn along the layer stacking direction $\Gamma$-$A$. In addition, the mirror Chern number $C_{i}$ protected by the mirror plane $\overline{M}_{z}$ ($k_z$=0) changes from 2 in KHgSb to 3 in BaHgSn. Therefore, when a compressive uniaxial strain is applied along the $y$ axis to break the rotation symmetry protecting the DSM state, BaHgSn becomes a strong topological insulator with $Z_{2}$ indices of $(1;000)$ and the topological surface Dirac cone co-exists with HSSs on the (010) surface. The Wilson-loop spectra have been calculated to verify these topological features. The calculated surface states, the Fermi surfaces and their quasiparticle interference patterns are ready to be compared with experimental measurements.
- arXiv:1912.04258 (replaced) [pdf, other]
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Title: Odd-frequency spin-triplet instability in disordered electron liquidComments: 27 pages, 8 figuresSubjects: Strongly Correlated Electrons (cond-mat.str-el)
We consider a two-dimensional disordered conductor in the regime when the superconducting phase is destroyed by the magnetic field. We observe that the end point of the superconductivity is a quantum critical point separating the conventional superconducting phase from a state with the odd-frequency spin-triplet pairing instability. We speculate that this could shed light on a rather mysterious insulating state observed in strongly disordered superconducting films in a broad region of the magnetic fields.
- arXiv:1912.05747 (replaced) [pdf, ps, other]
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Title: Dynamics of a membrane coupled to an active fluidComments: accepted by Phys Rev EJournal-ref: Phys. Rev. E 101, 042601 (2020)Subjects: Soft Condensed Matter (cond-mat.soft); Biological Physics (physics.bio-ph)
The dynamics of a membrane coupled to an active fluid on top of a substrate is considered theoretically. It is assumed that the director field of the active fluid has rotational symmetry in the membrane plane. This situation is likely to be relevant for in vitro reconstructed actomyosin-membrane system. Different from a membrane coupled to a polar active fluid, this model predicts that only when the viscosity of the fluid above the membrane is sufficiently large, a contractile active fluid is able to slow down the relaxation of the membrane for perturbations with wavelength comparable to the thickness of the active fluid. Hence our model predicts a finite-wavelength instability in the limit of strong contractility, which is different from a membrane coupled to a polar active fluid. On the other hand, a membrane coupled to an extensile active fluid is always unstable against long wavelength perturbations due to splay induced flows.
- arXiv:1912.06937 (replaced) [pdf, other]
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Title: Shape transition and hydrodynamics of vesicles in tube flowComments: 31 pages, 14 figuresJournal-ref: Phys. Rev. Fluids 5:043602, 2020Subjects: Fluid Dynamics (physics.flu-dyn); Soft Condensed Matter (cond-mat.soft)
The steady motion and deformation of a lipid-bilayer vesicle translating through a circular tube in low Reynolds number pressure-driven flow are investigated numerically using an axisymmetric boundary element method. This fluid-structure interaction problem is determined by three dimensionless parameters: reduced volume (a measure of the vesicle asphericity), geometric confinement (the ratio of the vesicle effective radius to the tube radius), and capillary number (the ratio of viscous to bending forces). The physical constraints of a vesicle -- fixed surface area and enclosed volume when it is confined in a tube -- determine critical confinement beyond which it cannot pass through without rupturing its membrane. The simulated results are presented in a wide range of reduced volumes [0.6, 0.98] for different degrees of confinement; the reduced volume of 0.6 mimics red blood cells. We draw a phase diagram of vesicle shapes and propose a shape transition line separating the parachute-like shape region from the bullet-like one in the reduced volume versus confinement phase space. We show that the shape transition marks a change in the behavior of vesicle mobility, especially for highly deflated vesicles. Most importantly, high-resolution simulations make it possible for us to examine the hydrodynamic interaction between the wall boundary and the vesicle surface at conditions of very high confinement, thus providing the limiting behavior of several quantities of interest, such as the thickness of lubrication film, vesicle mobility and its length, and the extra pressure drop due to the presence of the vesicle. This extra pressure drop holds implications for the rheology of dilute vesicle suspensions. Furthermore, we present various correlations and discuss a number of practical applications.
- arXiv:1912.08474 (replaced) [pdf, other]
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Title: Time-dependent spectral functions of the Anderson impurity model in response to a quench with application to time-resolved photoemission spectroscopyComments: 22 pages, 15 figuresJournal-ref: Phys. Rev. B 101, 115117 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el)
We investigate several definitions of the time-dependent spectral function $A(\omega,t)$ of the Anderson impurity model following a quench and within the time-dependent numerical renormalization group method. In terms of the two-time retarded Green function $G^r(t_1,t_2)$, the definitions differ in the choice of the time variable $t$ with respect to $t_1$ and/or $t_2$. In a previous study [Nghiem {\it et al.} Phys. Rev. Lett. 119, 156601 (2017)], we investigated the spectral function, obtained from the Fourier transform of ${\rm Im}[G^r(t_1,t_2)]$ w.r.t. the time difference $t'=t_1-t_2$, with $t=t_2$. Here, we derivie expressions for the retarded Green function for the choices $t=t_1$ and the average time $t=(t_1+t_2)/2$, within the TDNRG approach. We compare and contrast the resulting $A(\omega,t)$ for the different choices of time reference. Expressions for the lesser, greater and advanced Green functions are also derived within TDNRG for all choices of time reference. The average time lesser Green function $G^<(\omega,t)$ is particularly interesting, as it determines the time-dependent occupied density of states $N(\omega,t)=G^<(\omega,t)/(2\pi i)$, a quantity that determines the photoemission current in time-resolved pump-probe photoemission spectroscopy. We present calculations for $N(\omega,t)$ for the Anderson model following a quench, and discuss the resulting time evolution of the spectral features, such as the Kondo resonance and high-energy peaks. We also discuss the issue of thermalization at long times for $N(\omega,t)$. Finally, we use the results for $N(\omega,t)$ to calculate the time-resolved photoemission current for the Anderson model following a quench (acting as the pump) and study the different behaviors that can be observed for different resolution times of a Gaussian probe pulse.
- arXiv:2001.02884 (replaced) [pdf, other]
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Title: Coherence of a driven electron spin qubit actively decoupled from quasi-static noiseAuthors: Takashi Nakajima, Akito Noiri, Kento Kawasaki, Jun Yoneda, Peter Stano, Shinichi Amaha, Tomohiro Otsuka, Kenta Takeda, Matthieu R. Delbecq, Giles Allison, Arne Ludwig, Andreas D. Wieck, Daniel Loss, Seigo TaruchaComments: 10 pages, 7 figuresJournal-ref: Phys. Rev. X 10, 011060 (2020)Subjects: Quantum Physics (quant-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
The coherence of electron spin qubits in semiconductor quantum dots suffers mostly from low-frequency noise. During the last decade, efforts have been devoted to mitigate such noise by material engineering, leading to substantial enhancement of the spin dephasing time for an idling qubit. However, the role of the environmental noise during spin manipulation, which determines the control fidelity, is less understood. We demonstrate an electron spin qubit whose coherence in the driven evolution is limited by high-frequency charge noise rather than the quasi-static noise inherent to any semiconductor device. We employed a feedback control technique to actively suppress the latter, demonstrating a $\pi$-flip gate fidelity as high as $99.04\pm 0.23\,\%$ in a gallium arsenide quantum dot. We show that the driven-evolution coherence is limited by the longitudinal noise at the Rabi frequency, whose spectrum resembles the $1/f$ noise observed in isotopically purified silicon qubits.
- arXiv:2001.03419 (replaced) [pdf, other]
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Title: Universal Error Bound for Constrained Quantum DynamicsComments: 5 pages, 3 figures. Accompanying paper arXiv:2001.03421. Here, we prove the asymptotic bound and provide general ideas for the many-body generalization, which is numerically demonstratedJournal-ref: Phys. Rev. Lett. 124, 210606 (2020)Subjects: Quantum Physics (quant-ph); Quantum Gases (cond-mat.quant-gas); Statistical Mechanics (cond-mat.stat-mech); Strongly Correlated Electrons (cond-mat.str-el); Mathematical Physics (math-ph)
It is well known in quantum mechanics that a large energy gap between a Hilbert subspace of specific interest and the remainder of the spectrum can suppress transitions from the quantum states inside the subspace to those outside due to additional couplings that mix these states, and thus approximately lead to a constrained dynamics within the subspace. While this statement has widely been used to approximate quantum dynamics in various contexts, a general and quantitative justification stays lacking. Here we establish an observable-based error bound for such a constrained-dynamics approximation in generic gapped quantum systems. This universal bound is a linear function of time that only involves the energy gap and coupling strength, provided that the latter is much smaller than the former. We demonstrate that either the intercept or the slope in the bound is asymptotically saturable by simple models. We generalize the result to quantum many-body systems with local interactions, for which the coupling strength diverges in the thermodynamic limit while the error is found to grow no faster than a power law $t^{d+1}$ in $d$ dimensions. Our work establishes a universal and rigorous result concerning nonequilibrium quantum dynamics.
- arXiv:2001.03421 (replaced) [pdf, other]
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Title: Error bounds for constrained dynamics in gapped quantum systems: Rigorous results and generalizationsComments: 19 pages, 9 figures. Accompanying letter arXiv:2001.03419. Here, we prove the exact (rather than asymptotic) bound and rigorously derive the many-body bound without numerical demonstration. Generalization to open systems is also discussedJournal-ref: Phys. Rev. A 101, 052122 (2020)Subjects: Quantum Physics (quant-ph); Quantum Gases (cond-mat.quant-gas); Statistical Mechanics (cond-mat.stat-mech); Strongly Correlated Electrons (cond-mat.str-el); Mathematical Physics (math-ph)
In arXiv:2001.03419 we introduce a universal error bound for constrained unitary dynamics within a well-gapped energy band of an isolated quantum system. Here, we provide the full details on the derivation of the bound. In addition, we generalize the result to isolated quantum many-body systems by employing the local Schrieffer-Wolff transformation, obtaining an error bound that grows polynomially in time. We also generalize the result to Markovian open quantum systems and quantitatively explain the quantum Zeno effect.
- arXiv:2001.07893 (replaced) [pdf, ps, other]
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Title: Transport in two dimensional Rashba electron systems doped with interacting magnetic impuritiesComments: 14 pages, 12 figuresJournal-ref: Phys. Rev. B 101, 115412 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We study the transport properties of two dimensional electron systems with strong Rashba spin-orbit coupling (SOC) doped with interacting magnetic impurities. Interactions between magnetic impurities cause the formation of magnetic clusters with temperature dependent mean sizes (CMSs) distributed randomly on the surface of the system. Treating magnetic clusters as scattering centers, by employing a generalized relaxation time approximation we obtain the non-equilibrium distribution functions of Rashba electrons in both regimes of above and below the band-crossing point (BCP) and present the explicit forms of the conductivity in terms of effective relaxation times. We demonstrate that the combined effects of SOC and magnetic clusters cause the system to be anisotropic and the magneto-resistance strongly depends on both the clusters' mean size and spin, the strengths of SOC and the location of Fermi energy with respect to the BCP. Our results show that there are many contrasts between the transport properties of the system in the two regimes of above and below the BCP. By comparing the anisotropic magneto-resistance (AMR) of the two dimensional Rashba systems with the surface AMR of three dimensional magnetic topological insulators, we also point out the differences between these systems.
- arXiv:2002.03234 (replaced) [pdf, ps, other]
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Title: The dissipation-time uncertainty relationComments: Supplemented by detailed derivationsSubjects: Statistical Mechanics (cond-mat.stat-mech); Soft Condensed Matter (cond-mat.soft); Chaotic Dynamics (nlin.CD); Biological Physics (physics.bio-ph)
We show that the dissipation rate bounds the rate at which physical processes can be performed in stochastic systems far from equilibrium. Namely, for rare processes we prove the fundamental tradeoff $\langle \dot S_\text{e} \rangle \mathcal{T} \geq k_{\text{B}} $ between the entropy flow $\langle \dot S_\text{e} \rangle$ into the reservoirs and the mean time $\mathcal{T}$ to complete a process. This dissipation-time uncertainty relation is a novel form of speed limit: the smaller the dissipation, the larger the time to perform a process.
- arXiv:2002.05065 (replaced) [pdf, other]
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Title: Imaging the breakdown of ohmic transport in grapheneAuthors: A. Jenkins, S. Baumann, H. Zhou, S. A. Meynell, D. Yang, K. Watanabe, T. Taniguchi, A. Lucas, A. F. Young, A. C. Bleszynski JayichComments: Fixed colorscale label Fig. 3bSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Ohm's law describes the proportionality of current density and electric field. In solid-state conductors, Ohm's law emerges due to electron scattering processes that relax the electrical current. Here, we use nitrogen-vacancy center magnetometry to directly image the local breakdown of Ohm's law in a narrow constriction fabricated in a high mobility graphene monolayer. Ohmic flow is visible at room temperature as current concentration on the constriction edges, with flow profiles entirely determined by sample geometry. However, as the temperature is lowered below 200 K, the current concentrates near the constriction center. The change in the flow pattern is consistent with a crossover from diffusive to viscous electron transport dominated by electron-electron scattering processes that do not relax current.
- arXiv:2002.11556 (replaced) [pdf, other]
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Title: Nonequilibrium Phase Transitions in Repulsive Binary MixturesSubjects: Statistical Mechanics (cond-mat.stat-mech); Soft Condensed Matter (cond-mat.soft)
We consider rapid cooling processes in classical, 3-dimensional, purely repulsive binary mixtures in which an initial infinite-temperature configuration is instantly quenched to zero temperature. It is found that such systems display both kinds of possible continuous nonequilibrium transition, characterized by either a conserved or non-conserved order parameter. The type of transition that is observed can be controlled by tuning the interactions between unlike particles, with strong inter-species repulsion leading to chemical ordering in terms of an unmixing process, whereas weak repulsion gives rise to spontaneous crystallization, maintaining chemical homogeneity. In contrast to common first-order equilibrium freezing transitions, this nonequilibrium crystallization phenomenon is continuous in nature, being barrierless and producing grain-size distributions that display scale-invariant features. Furthermore, the results suggest that the dual-type transition behavior is universal for repulsive pair interaction potential-energy functions in general, with the propensity for the continuous freezing transition being related to their behavior in the neighborhood of zero separation.
- arXiv:2002.11859 (replaced) [pdf, other]
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Title: Combining Laue diffraction with Bragg coherent diffraction imaging at 34-ID-CAuthors: Anastasios Pateras, Ross Harder, Wonsuk Cha, Jonathan G. Gigax, J. Kevin Baldwin, Jon Tischler, Ruqing Xu, Wenjun Liu, Mark J. Erdmann, Robert Kalt, Richard L. Sandberg, Saryu Fensin, Reeju PokharelSubjects: Instrumentation and Detectors (physics.ins-det); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci)
Measurement modalities in Bragg coherent diffraction imaging (BCDI) rely on finding signal from a single nanoscale crystal object, which satisfies the Bragg condition among a large number of arbitrarily oriented nanocrystals. However, even when the signal from a single Bragg reflection with (hkl) Miller indices is found, the crystallographic axes on the retrieved three-dimensional (3D) image of the crystal remain unknown, and thus, localizing in reciprocal space other Bragg reflections becomes in reality impossible or requires good knowledge of the orientation of the crystal. We report the commissioning of a movable double-bounce Si (111) monochromator at the 34-ID-C end station of the Advanced Photon Source, which aims at delivering multi-reflection BCDI as a standard tool in a single beamline instrument. The new instrument enables this through rapid switching from monochromatic to broadband (pink) beam permitting the use of Laue diffraction to determine crystal orientation. With a proper orientation matrix determined for the lattice, one can measure coherent diffraction near multiple Bragg peaks, thus providing sufficient information to image the full strain tensor in 3D. We discuss the design, concept of operation, the developed procedures for indexing Laue patterns, and automated measuring of Bragg coherent diffraction data from multiple reflections of the same nanocrystal.
- arXiv:2002.12603 (replaced) [pdf, other]
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Title: Derivative structure enumeration using binary decision diagramAuthors: Kohei Shinohara, Atsuto Seko, Takashi Horiyama, Masakazu Ishihata, Junya Honda, Isao TanakaSubjects: Computational Physics (physics.comp-ph); Materials Science (cond-mat.mtrl-sci)
A derivative structure is a nonequivalent substitutional atomic configuration derived from a given primitive cell. The enumeration of derivative structures plays an essential role in searching for the ground states in multicomponent systems. However, it is computationally hard to enumerate derivative structures if the number of derivative structures of a target system becomes huge. In the present study, we introduce a novel compact data structure of the zero-suppressed binary decision diagram (ZDD) to enumerate derivative structures much more efficiently. The present study shows its simple applications to the enumeration of structures derived from the face-centered cubic and hexagonal close-packed lattices in binary, ternary, and quaternary systems. The present ZDD-based procedure should significantly contribute not only to various computational approaches based on the derivative structures but also to a wide range of combinatorial issues in physics and materials science.
- arXiv:2002.12932 (replaced) [pdf, ps, other]
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Title: Non-Liquid Cellular StatesAuthors: Juven WangComments: 42 pages. Subtitle: Gluing Gauge-(Higher)-Symmetry-Breaking vs -Extension Interfacial DefectsSubjects: Strongly Correlated Electrons (cond-mat.str-el); High Energy Physics - Theory (hep-th); Mathematical Physics (math-ph); Quantum Physics (quant-ph)
The existence of quantum non-liquid states and fracton orders, both gapped and gapless states, challenges our understanding of phases of entangled matter. We generalize Wen's cellular topological states to liquid or non-liquid cellular states. We propose a mechanism to construct more general non-abelian states by gluing gauge-symmetry-breaking vs gauge-symmetry-extension interfaces as extended defects in a cellular network, including defects of higher-symmetries. Our approach also includes the anyonic particle/string condensation and composite string (p-string)/membrane condensations. This also shows gluing the familiar extended topological quantum field theory or conformal field theory data via topology, geometry, and renormalization consistency criteria (via certain modified group cohomology or cobordism theory data) in a tensor network can still guide us to analyze the non-liquid states. (Part of the abelian construction can be understood from the K-matrix Chern-Simons theory approach and coupled-layer-by-junction constructions.) This may also lead us toward a unifying framework for quantum systems of both higher-symmetries and sub-system/sub-dimensional symmetries.
- arXiv:2003.01368 (replaced) [pdf, other]
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Title: What renders bulk metallic glass ductile/brittle? -- new insight from the medium-range orderSubjects: Materials Science (cond-mat.mtrl-sci); Disordered Systems and Neural Networks (cond-mat.dis-nn); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Understanding ductility or brittleness of monolithic bulk metallic glasses (BMGs) requires detailed knowledge of the amorphous structure. The medium range order (MRO) of ductile Pd$_{40}$Ni$_{40}$P$_{20}$ and brittle Zr$_{52.5}$Cu$_{17.9}$Ni$_{14.6}$Al$_{10}$Ti$_5$ (Vit105) was characterized prior to and after notched 3-point bending tests using variable-resolution fuctuation electron microscopy. Here we show the presence of a second larger MRO correlation length in the ductile material which is not present in the brittle material. A comparison with literature suggests that the larger correlation length accounts for larger shear transformation zones (STZs) which increase the heterogeneity. This enables an easier shear band formation and thus explains the difference in deformability.
- arXiv:2003.01702 (replaced) [pdf, other]
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Title: Generalised hydrodynamics with dephasing noiseComments: 7+7 pages, 2 figuresSubjects: Statistical Mechanics (cond-mat.stat-mech); Quantum Gases (cond-mat.quant-gas); Strongly Correlated Electrons (cond-mat.str-el)
We consider the out-of-equilibrium dynamics of an interacting integrable system in the presence of an external dephasing noise. In the limit of large spatial correlation of the noise, we develop an exact description of the dynamics of the system based on a hydrodynamic formulation. This results in an additional term to the standard generalized hydrodynamics theory describing diffusive dynamics in the momentum space of the quasiparticles of the system, with a time- and momentum-dependent diffusion constant. Our analytical predictions are then benchmarked in the classical limit by comparison with a microscopic simulation of the non-linear Schrodinger equation, showing perfect agreement. In the quantum case, our predictions agree with state-of-the-art numerical simulations of the anisotropic Heisenberg spin in the accessible regime of times and with bosonization predictions in the limit of small dephasing times and temperatures.
- arXiv:2003.03117 (replaced) [pdf, other]
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Title: Superconducting properties of the hole-doped three-band \emph{d-p} model studied with minimal-size real-space \emph{d}-wave pairing operatorsSubjects: Superconductivity (cond-mat.supr-con); Strongly Correlated Electrons (cond-mat.str-el)
The three-band \emph{d-p} model is investigated by means of Variational Monte-Carlo (VMC) method with the BCS-like wave-function supplemented by the Gutzwiller and Jastrow correlators. The VMC optimization leads to $d$-$wave$ superconducting state with a characteristic dome-like shape of the order parameter for hole doping $\delta \lesssim 0.4$, in a good agreement with the experimental observations. Also, the off-diagonal pair-pair correlation functions, calculated within VMC, vindicates the results obtained very recently within the diagrammatic expansion of the Gutzwiller wave function method (DE-GWF) [cf. Phys. Rev. B \textbf{99}, 104511 (2019)]. Subsequently, the nature of the $d$-$wave$ pairing is investigated by means of recently proposed \emph{minimal-size real-space d-wave pairing operators} [Phys. Rev. B \textbf{100}, 214502 (2019)]. An emergence of the long-range superconducting ordering for both $d$ and $p$ orbitals is reported by analysing the corresponding off-diagonal pair-pair correlation functions. The dominant character of \emph{d-wave} pairing on $d$ orbitals is confirmed. Additionally, the trial wave-function is used to investigate the magnetic properties of the system. The analysis of spin-spin correlation functions is carried out and shows antiferromagnetic $\mathbf{q}=(\pi,\pi)$, short-range order, as expected. For the sake of completeness, the charge gap has been estimated, which for the parent compound takes the value $\Delta_{CG}\approx1.78\pm0.51\text{ eV}$, and agrees with values reported experimentally for the cuprates.
- arXiv:2003.04166 (replaced) [pdf, other]
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Title: Learning entropy production via neural networksComments: 10 pages, 8 figuresSubjects: Statistical Mechanics (cond-mat.stat-mech); Machine Learning (cs.LG); Machine Learning (stat.ML)
This Letter presents a neural estimator for entropy production, or NEEP, that estimates entropy production (EP) from trajectories without any prior knowledge of the system. For steady state, we rigorously prove that the estimator, which can be built up from different choices of deep neural networks, provides stochastic EP by optimizing the objective function proposed here. We verify the NEEP with the stochastic processes of the bead-spring and discrete flashing ratchet models, and also demonstrate that our method is applicable to high-dimensional data and non-Markovian systems.
- arXiv:2003.05087 (replaced) [pdf, other]
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Title: Machine learning in physics: The pitfalls of poisoned training setsComments: 5 pages, 3 figures, 3 tablesSubjects: Disordered Systems and Neural Networks (cond-mat.dis-nn)
Known for their ability to identify hidden patterns in data, artificial neural networks are among the most powerful machine learning tools. Most notably, neural networks have played a central role in identifying states of matter and phase transitions across condensed matter physics. To date, most studies have focused on systems where different phases of matter and their phase transitions are known, and thus the performance of neural networks is well controlled. While neural networks present an exciting new tool to detect new phases of matter, here we demonstrate that when the training sets are poisoned (i.e., poor training data or mislabeled data) it is easy for neural networks to make misleading predictions.
- arXiv:2003.05850 (replaced) [pdf, other]
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Title: Toward a room temperature Schafroth superconductor based on charged excitonic complexesAuthors: Z. Sun, J. Beaumariage, Q. Cao, K. Watanabe, T. Taniguchi, B. Hunt, I. V. Bondarev, D. W. SnokeSubjects: Superconductivity (cond-mat.supr-con)
In 1954, Schafroth proposed a mechanism for superconductivity that is physically possible, but ended up not being the explanation of the well known BCS superconductors. The proposal argued correctly that a Bose condensate of charged bosons should also be a superconductor. In 1996, V.I. Yudson proposed a way to produce a charged boson by attaching two free charges to an exciton in a semiconductor, to make a "quaternion". While that state was never seen in III-V semiconductors, our calculations show that it is predicted to be stable in structures made with monolayers of transition metal dichalcogenide (TMD) materials. We present experimental spectroscopic measurements that agree with this theory, which indicate that we have observed this charged-boson state in this type of structure. This opens up a new path for pursuing room temperature superconductivity.
- arXiv:cond-mat/0512492 (replaced) [pdf, ps, other]
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Title: Levy--Brownian motion on finite intervals: Mean first passage time analysisComments: 9 pages, 13 figuresJournal-ref: Phys. Rev. E 73, 046104 (2006)Subjects: Statistical Mechanics (cond-mat.stat-mech); Other Condensed Matter (cond-mat.other)
We present the analysis of the first passage time problem on a finite interval for the generalized Wiener process that is driven by L\'evy stable noises. The complexity of the first passage time statistics (mean first passage time, cumulative first passage time distribution) is elucidated together with a discussion of the proper setup of corresponding boundary conditions that correctly yield the statistics of first passages for these non-Gaussian noises. The validity of the method is tested numerically and compared against analytical formulae when the stability index $\alpha$ approaches 2, recovering in this limit the standard results for the Fokker-Planck dynamics driven by Gaussian white noise.
- arXiv:1008.4246 (replaced) [pdf, ps, other]
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Title: Lévy Ratchet in a Weak Noise Limit: Theory and SimulationComments: 14 pages, 11 figures, 63 referencesJournal-ref: Eur. Phys. J. ST 191, 223 (2010)Subjects: Statistical Mechanics (cond-mat.stat-mech); Mathematical Physics (math-ph)
We study the motion of a particle embedded in a time independent periodic potential with broken mirror symmetry and subjected to a L\'evy noise possessing L\'evy stable probability law (L\'evy ratchet). We develop analytical approach to the problem based on the asymptotic probabilistic method of decomposition proposed by P. Imkeller and I. Pavlyukevich [J. Phys. A {\bf39}, L237 (2006); Stoch. Proc. Appl. {\bf116}, 611 (2006)]. We derive analytical expressions for the quantities characterizing the particle motion, namely the splitting probabilities of first escape from a single well, the transition probabilities and the particle current. A particular attention is devoted to the interplay between the asymmetry of the ratchet potential and the asymmetry (skewness) of the L\'evy noise. Intensive numerical simulations demonstrate a good agreement with the analytical predictions for sufficiently small intensities of the L\'evy noise driving the particle.
- arXiv:1406.7096 (replaced) [pdf, other]
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Title: Escape from bounded domains driven by multi-variate $α$-stable noisesComments: 8 pages, 5 figuresJournal-ref: J. Stat. Mech. P06031 (2015)Subjects: Statistical Mechanics (cond-mat.stat-mech)
In this paper we provide an analysis of a mean first passage time problem of a random walker subject to a bi-variate $\alpha$-stable L\'evy type noise from a 2-dimensional disk. For an appropriate choice of parameters the mean first passage time reveals non-trivial, non-monotonous dependence on the stability index $\alpha$ describing jumps' length asymptotics both for spherical and Cartesian L\'evy flights. Finally, we study escape from $d$-dimensional hyper-sphere showing that $d$-dimensional escape process can be used to discriminate between various types of multi-variate $\alpha$-stable noises, especially spherical and Cartesian L\'evy flights.
- arXiv:1406.7810 (replaced) [pdf, other]
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Title: Resonant activation in 2D and 3D systems driven by multi-variate Lévy noisesComments: 7 pages, 4 figuresJournal-ref: J. Stat. Mech. P09022 (2014)Subjects: Statistical Mechanics (cond-mat.stat-mech)
Resonant activation is one of classical effects demonstrating constructive role of noise. In resonant activation cooperative action of barrier modulation process and noise lead to the optimal escape kinetics as measured by the mean first passage time. Resonant activation has been observed in versatilities of systems for various types of barrier modulation processes and noise types. Here, we show that resonant activation is also observed in 2D and 3D systems driven by bi-variate and tri-variate $\alpha$-stable noises. Strength of resonant activation is sensitive to the exact value of the noise parameters. In particular, the decrease in the stability index $\alpha$ results in the disappearance of the resonant activation.
- arXiv:1808.03503 (replaced) [pdf, other]
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Title: Characteristic time and length scales in melts of Kremer-Grest bead-spring polymers with wormlike bending stiffnessComments: Complete rewrite compared to previous versionJournal-ref: Macromolecules 2020Subjects: Soft Condensed Matter (cond-mat.soft)
The Kremer-Grest (KG) model is a standard for studying generic polymer properties. Here we have equilibrated KG melts up to and beyond $200$ entanglements per chain for varying chain stiffness. We present methods for estimating the Kuhn length corrected for incompressibility effects, for estimating the entanglement length corrected for chain stiffness, for estimating bead frictions and Kuhn times taking into account entanglement effects. These are the key parameters for enabling quantitative, accurate, and parameter free comparisons between theory, experiment and simulations of KG polymer models with varying stiffness. We demonstrate this for the mean-square monomer displacements in moderately to highly entangled melts as well as for the shear relaxation modulus for unentangled melts, which are found to be in excellent agreement with the predictions from standard theories of polymer dynamics.
- arXiv:1808.03509 (replaced) [pdf, ps, other]
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Title: Kremer-Grest models for commodity polymer melts: Linking theory, experiment and simulation at the Kuhn scaleComments: Compared to previous versions. Final update and corrections to numbers in tablesJournal-ref: Macromolecules 2020Subjects: Soft Condensed Matter (cond-mat.soft)
The Kremer-Grest (KG) polymer model is a standard model for studying generic polymer properties in Molecular Dynamics simulations. It owes its popularity to its simplicity and computational efficiency, rather than its ability to represent specific polymers species and conditions. Here we show, that by tuning the chain stiffness it is possible to adapt the KG model to model melts of real polymers. In particular, we provide mapping relations from KG to SI units for a wide range of commodity polymers. The connection between the experimental and the KG melts is made at the Kuhn scale, i.e. at the crossover from chemistry-specific small scale to the universal large scale behavior. We expect Kuhn scale-mapped KG models to faithfully represent universal properties dominated by the large scale conformational statistics and dynamics of flexible polymers. In particular, we observe very good agreement between entanglement moduli of our KG models and the experimental moduli of the target polymers.
- arXiv:1906.01888 (replaced) [pdf, other]
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Title: Screening and the Pinch Point Paradox in Spin IceComments: 14 pages, 9 figuresJournal-ref: Phys. Rev. Research 2, 013305 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el); Materials Science (cond-mat.mtrl-sci)
A pinch point singularity in the structure factor characterizes an important class of condensed matter that is a counterpoint to the paradigm of broken symmetry. This class includes water ice, charge ice and spin ice. Of these, dipolar spin ice affords the the pre-eminent model system because it has a well-established Hamiltonian, is simple enough to allow analytical theory and numerical simulation, and is well represented in experiment by Dy$_{2}$Ti$_{2}$O$_{7}$ and Ho$_{2}$Ti$_{2}$O$_{7}$. Nevertheless it is a considerable challenge to resolve the pinch points in simulation or experiment as they represent a very long range correlation. Here we present very high resolution simulations of the polarized neutron scattering structure factor of dipolar spin ice and new analytical theory of the pinch point profiles. We compare these with existing theory and experiment. We find that our simulations are consistent with theories that reveal the pinch points to be infinitely sharp, as a result of unscreened dipolar fields. However, neither simulation nor these theories are consistent with experiments, which instead is quantitatively captured by a theory that allows for screening of the dipolar fields and consequent strong broadening of the pinch points. This striking paradox is not easily resolved: broadening of the pinch points by random disorder seems to have been ruled out by existing theory, while deficiencies in the Hamiltonian description are not relevant. Intriguingly, we are left to consider the role of quantum fluctuations or the possibility of a fundamental correction to either the standard method of simulating dipolar systems, or the theory of polarized neutron scattering. More generally, our results may have relevance far beyond ice systems. For example, spin ice is a model Debye-H\"uckel (magnetic) electrolyte, so our basic observation that the screening length may diverge while...
- arXiv:1906.07387 (replaced) [pdf, other]
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Title: The existence of robust edge currents in Sierpinsky FractalsComments: V1: 5 pages, 6 figures, 1 table; V2: Changed titleJournal-ref: Phys. Rev. Research 2, 013044 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el)
We investigate the Hall conductivity in a Sierpinski carpet, a fractal of Hausdorff dimension $d_f=\ln(8)/\ln(3) \approx 1.893$, subject to a perpendicular magnetic field. We compute the Hall conductivity using linear response and the recursive Green function method. Our main finding is that edge modes, corresponding to a maximum Hall conductivity of at least $\sigma_{xy}=\pm \frac{e^2}{h}$, seems to be generically present for arbitrary finite field strength, no mater how one approaches the thermodynamic limit of the fractal. We discuss a simple counting rule to determine the maximal number of edge modes in terms of paths through the system with a fixed width. This quantized edge conductance, as in the case of the conventional Hofstadter problem, is stable with respect to disorder and thus a robust feature of the system.
- arXiv:1906.11142 (replaced) [pdf, other]
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Title: Strain-induced stripe phase in charge ordered single layer NbSe$_2$Journal-ref: NPG Asia Mater 12, 24 (2020)Subjects: Materials Science (cond-mat.mtrl-sci); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Strongly Correlated Electrons (cond-mat.str-el)
Charge density waves are ubiquitous phenomena in metallic transition metal dichalcogenides. In NbSe$_2$, a triangular $3\times3$ structural modulation is coupled to a charge modulation. Recent experiments reported evidence for a triangular-stripe transition at the surface, due to strain or accidental doping and associated to a $4\times4$ modulation. We employ \textit{ab-initio} calculations to investigate the strain-induced structural instabilities in a pristine single layer and analyse the energy hierarchy of the structural and charge modulations. Our results support the observation of phase separation between triangular and stripe phases in 1H-NbSe$_2$, relating the stripe phase to compressive isotropic strain, favouring the $4\times4$ modulation. The observed wavelength of the charge modulation is also reproduced with good accuracy.
- arXiv:1907.04107 (replaced) [pdf, other]
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Title: Rabi oscillations in a superconducting nanowire circuitAuthors: Yannick Schön, Jan Nicolas Voss, Micha Wildermuth, Andre Schneider, Sebastian T. Skacel, Martin P. Weides, Jared H. Cole, Hannes Rotzinger, Alexey V. UstinovSubjects: Superconductivity (cond-mat.supr-con); Disordered Systems and Neural Networks (cond-mat.dis-nn); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Quantum Physics (quant-ph)
We investigate the circuit quantum electrodynamics of anharmonic superconducting nanowire oscillators. The sample circuit consists of a capacitively shunted nanowire with a width of about 20 nm and a varying length up to 350 nm, capacitively coupled to an on-chip resonator. By applying microwave pulses we observe Rabi oscillations, measure coherence times and the anharmonicity of the circuit. Despite the very compact design, simple top-down fabrication and high degree of disorder in the oxidized (granular) aluminum material used, we observe lifetimes in the microsecond range.
- arXiv:1908.02045 (replaced) [pdf]
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Title: On the influence of uncertainties in scattering potentials on quantitative analysis using keV ionsJournal-ref: Nucl. Inst. Methods Phys. Res. B 470 (2020), 21-27Subjects: Materials Science (cond-mat.mtrl-sci)
Experimental spectra from medium energy ion scattering were compared to Monte-Carlo simulations (employing the TRBS code) to obtain information on the scattering potential. The impact of uncertainties in the interatomic potential on quantification of sample properties such as thickness, composition or electronic stopping was investigated for different scattering geometries: backscattering and transmission. For backscattered He ions with tens of keV primary energy the scattering potential was found to overestimate the multiple scattering background in the energy spectra resulting in an uncertainty of < 3 % in quantitative analysis. Light ions transmitted through a sample for equivalent path length in the medium are only affected minorly by changes in the scattering potential. This effect becomes more distinct for heavier primary ions.
- arXiv:1908.08495 (replaced) [pdf, other]
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Title: Applying machine learning optimization methods to the production of a quantum gasAuthors: Adam J. Barker, Harry Style, Kathrin Luksch, Shinichi Sunami, David Garrick, Felix Hill, Christopher J. Foot, Elliot BentineComments: 19 pages, 7 figures, 1 tableJournal-ref: Mach. Learn.: Sci. Technol. 1 015007 (2020)Subjects: Quantum Gases (cond-mat.quant-gas); Atomic Physics (physics.atom-ph); Computational Physics (physics.comp-ph)
We apply three machine learning strategies to optimize the atomic cooling processes utilized in the production of a Bose-Einstein condensate (BEC). For the first time, we optimize both laser cooling and evaporative cooling mechanisms simultaneously. We present the results of an evolutionary optimization method (Differential Evolution), a method based on non-parametric inference (Gaussian Process regression) and a gradient-based function approximator (Artificial Neural Network). Online optimization is performed using no prior knowledge of the apparatus, and the learner succeeds in creating a BEC from completely randomized initial parameters. Optimizing these cooling processes results in a factor of four increase in BEC atom number compared to our manually-optimized parameters. This automated approach can maintain close-to-optimal performance in long-term operation. Furthermore, we show that machine learning techniques can be used to identify the main sources of instability within the apparatus.
- arXiv:1909.00196 (replaced) [pdf, other]
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Title: Peculiarities of escape kinetics in the presence of athermal noisesComments: 12 pagesJournal-ref: Chaos 30, 013127 (2020)Subjects: Statistical Mechanics (cond-mat.stat-mech)
Stochastic evolution of various dynamic systems and reaction networks is commonly described in terms of noise assisted escape of an overdamped particle from a potential well, as devised by the paradigmatic Langevin equation in which additive Gaussian stochastic force reproduces effects of thermal fluctuations from the reservoir. When implemented for systems close to equilibrium, the approach correctly explains emergence of Boltzmann distribution for the ensemble of trajectories generated by Langevin equation and relates intensity of the noise strength to the mobility.
This scenario can be further generalized to include effects of non-Gaussian, burst-like forcing modeled by L\'evy noise. In this case however, the pulsatile additive noise cannot be treated as the internal (thermal), since the relation between the strength of the friction and variance of the noise is violated.
Heavy tails of L\'evy noise distributions not only facilitate escape kinetics, but more importantly, change the escape protocol by altering final stationary state to a non-Boltzmann, non-equilibrium form. As a result,
contrary to the kinetics induced by a Gaussian white noise, escape rates in environments with L\'evy noise are determined not by the barrier height, but instead, by the barrier width.
We further discuss consequences of simultaneous action of thermal and L\'evy noises on statistics of passage times and population of reactants in double-well potentials. - arXiv:1910.01630 (replaced) [pdf, other]
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Title: Strong planar subsystem symmetry-protected topological phases and their dual fracton ordersComments: 21 pages, 7 figuresJournal-ref: Phys. Rev. Research 2, 012059(R) (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el); Statistical Mechanics (cond-mat.stat-mech); High Energy Physics - Theory (hep-th); Quantum Physics (quant-ph)
We classify subsystem symmetry-protected topological (SSPT) phases in $3+1$D protected by planar subsystem symmetries, which are dual to abelian fracton topological orders. We distinguish between weak SSPTs, which can be constructed by stacking $2+1$D SPTs, and strong SSPTs, which cannot. We identify signatures of strong phases, and show by explicit construction that such phases exist. A classification of strong phases is presented for an arbitrary finite abelian group. Finally, we show that fracton orders realizable via $p$-string condensation are dual to weak SSPTs, while strong SSPTs do not admit such a realization.
- arXiv:1910.03504 (replaced) [pdf, other]
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Title: Random-link matching problems on random regular graphsJournal-ref: J. Stat. Mech. (2020) 033301Subjects: Disordered Systems and Neural Networks (cond-mat.dis-nn); Mathematical Physics (math-ph)
We study the random-link matching problem on random regular graphs, alongside with two relaxed versions of the problem, namely the fractional matching and the so-called "loopy" fractional matching. We estimated the asymptotic average optimal cost using the cavity method. Moreover, we also study the finite-size corrections due to rare topological structures appearing in the graph at large sizes. We estimate these contributions using the cavity approach, and we compare our results with the output of numerical simulations. The analysis also clarifies the meaning of the finite-size contributions appearing in the fully-connected version of the problem, that has been already analyzed in the literature.
- arXiv:1910.05938 (replaced) [pdf, other]
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Title: Appearance of hinge states in second-order topological insulators via the cutting procedureComments: 17 pages, 13 figuresJournal-ref: Phys. Rev. B 101, 115120 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
In recent years, second-order topological insulators have been proposed as a new class of topological insulators. Second-order topological insulators are materials with gapped bulk and surfaces, but with topologically protected gapless states at the intersection of two surfaces. These gapless states are called hinge states. In this paper, we give a general proof that any insulators with inversion symmetry and gapped surface in class A always have hinge states when the $\mathbb{Z}_{4}$ topological index $\mu_{1}$ is $\mu_{1}=2$. We consider a three-dimensional insulator whose boundary conditions along two directions change by changing the hopping amplitudes across the boundaries. We study behaviors of gapless states through continuously changing boundary conditions along the two directions, and reveal that the behaviors of gapless states result from the $\mathbb{Z}_{4}$ strong topological index. From this discussion, we show that gapless states inevitably appear at the hinge of a three-dimensional insulator with gapped surfaces when the strong topological index is $\mathbb{Z}_{4}=2$ and the weak topological indices are $\nu_{1}=\nu_{2}=\nu_{3}=0$.
- arXiv:1910.08030 (replaced) [pdf, other]
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Title: Three-dimensional time-reversal-invariant Hofstadter-Hubbard modelComments: 6 pages, 3 figures + 2 pages, 2 figuresJournal-ref: Phys. Rev. Research 2, 013299 (2020)Subjects: Quantum Gases (cond-mat.quant-gas); Strongly Correlated Electrons (cond-mat.str-el); Quantum Physics (quant-ph)
We report on the three-dimensional time-reversal-invariant Hofstadter model with finite spin-orbit coupling. We introduce three numerical methods for characterizing the topological phases based on twisted boundary conditions, Wilson loops, as well as the local topological marker. Besides the weak and strong topological insulator phases we find a nodal line semimetal in the parameter regime between the two three-dimensional topological insulator phases. Using dynamical mean-field theory combined with the topological Hamiltonian approach we find stabilization of these three-dimensional topological states due to the Hubbard interaction. We study surface states which exhibit an asymmetry between left and right surface originating from the broken parity symmetry of the system. Our results set the stage for further research on inhomogeneous three-dimensional topological systems, proximity effects, topological Mott insulators and non-trivially linked nodal line semimetals.
- arXiv:1911.06509 (replaced) [pdf, ps, other]
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Title: Improved algorithm for neuronal ensemble inference by Monte Carlo methodComments: 14 pages, 3 figuresJournal-ref: Proceedings of NetSci-X 2020, pp.77-90Subjects: Disordered Systems and Neural Networks (cond-mat.dis-nn); Machine Learning (cs.LG); Neurons and Cognition (q-bio.NC)
Neuronal ensemble inference is one of the significant problems in the study of biological neural networks. Various methods have been proposed for ensemble inference from their activity data taken experimentally. Here we focus on Bayesian inference approach for ensembles with generative model, which was proposed in recent work. However, this method requires large computational cost, and the result sometimes gets stuck in bad local maximum solution of Bayesian inference. In this work, we give improved Bayesian inference algorithm for these problems. We modify ensemble generation rule in Markov chain Monte Carlo method, and introduce the idea of simulated annealing for hyperparameter control. We also compare the performance of ensemble inference between our algorithm and the original one.
- arXiv:1911.08345 (replaced) [pdf, other]
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Title: Highly tunable exchange-only singlet-only qubit in a GaAs triple quantum dotComments: 5 pages, 3 figures, plus Supplemental MaterialJournal-ref: Phys. Rev. Research 2, 012062 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We propose an implementation of a singlet-only spin qubit in a GaAs-based triple quantum dot with a (1,4,1) charge occupation. In the central multi-electron dot, the interplay between Coulomb interaction and an out-of-plane magnetic field creates an energy spectrum with a tunable singlet-triplet splitting, which can be exploited to create a six-particle singlet-only qubit with a qubit splitting that can straightforwardly be tuned over tens of $\mu$eV by adjusting the external magnetic field. We confirm the full exchange-based electric control of the qubit and demonstrate its superior coherence properties due to its singlet-only nature.
- arXiv:2002.10555 (replaced) [pdf, other]
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Title: Coupling lattice instabilities across the interface in ultrathin oxide heterostructuresAuthors: T.C. van Thiel, J. Fowlie, C. Autieri, N. Manca, M. Šiškins, D. Afanasiev, S. Gariglio, A.D. CavigliaComments: 5 pages, 4 figuresSubjects: Materials Science (cond-mat.mtrl-sci); Strongly Correlated Electrons (cond-mat.str-el)
Oxide heterointerfaces constitute a rich platform for realizing novel functionalities in condensed matter. A key aspect is the strong link between structural and electronic properties, which can be modified by interfacing materials with distinct lattice symmetries. Here we determine the effect of the cubic-tetragonal distortion of $\text{SrTiO}_3$ on the electronic properties of thin films of $\text{SrIrO}_3$, a topological crystalline metal hosting a delicate interplay between spin-orbit coupling and electronic correlations. We demonstrate that below the transition temperature at 105 K, $\text{SrIrO}_3$ orthorhombic domains couple directly to tetragonal domains in $\text{SrTiO}_3$. This forces the in-phase rotational axis to lie in-plane and creates a binary domain structure in the $\text{SrIrO}_3$ film. The close proximity to the metal-insulator transition in ultrathin $\text{SrIrO}_3$ causes the individual domains to have strongly anisotropic transport properties, driven by a reduction of bandwidth along the in-phase axis. The strong structure-property relationships in perovskites make these compounds particularly suitable for static and dynamic coupling at interfaces, providing a promising route towards realizing novel functionalities in oxide heterostructures.
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Tue, 17 Mar 2020
- arXiv:2003.06483 [pdf]
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Title: Realization of the kagome spin ice state in a frustrated intermetallic compoundAuthors: Kan Zhao, Hao Deng, Hua Chen, Kate A. Ross, Vaclav Petříček, Gerrit Günther, Margarita Russina, Vladimir Hutanu, Philipp GegenwartComments: 4 figures and 2 tables, with the figures slightly different from the formal online versionJournal-ref: Science 367, 1218 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el); Materials Science (cond-mat.mtrl-sci)
Spin ices are exotic phases of matter characterized by frustrated spins obeying local ice rules, in analogy with the electric dipoles in water ice. In two dimensions, one can similarly define ice rules for in-plane Ising-like spins arranged on a kagome lattice. These ice rules require each triangle plaquette to have a single monopole, and can lead to various unique orders and excitations. Using experimental and theoretical approaches including magnetometry, thermodynamic measurements, neutron scattering and Monte Carlo simulations, we establish HoAgGe as a crystalline (i.e. non-artificial) system that realizes the kagome spin ice state. The system features a variety of partially and fully ordered states and a sequence of field-induced phases at low temperatures, all consistent with the kagome ice rule.
- arXiv:2003.06506 [pdf, other]
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Title: Variational and Diffusion Quantum Monte Carlo Calculations with the CASINO CodeSubjects: Computational Physics (physics.comp-ph); Materials Science (cond-mat.mtrl-sci)
We present an overview of the variational and diffusion quantum Monte Carlo methods as implemented in the CASINO program. We particularly focus on developments made in the last decade, describing state-of-the-art quantum Monte Carlo algorithms and software and discussing their strengths and their weaknesses. We review a range of recent applications of CASINO.
- arXiv:2003.06544 [pdf, other]
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Title: Enhanced longevity of the spin helix in low-symmetry quantum wellsComments: 12 pages, 6 figures. Comments welcomeSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
In a semiconductor, collective excitations of spin textures usually decay rather fast due to D'yakonov-Perel' spin relaxation. The latter arises from spin-orbit coupling, which induces wave-vector-dependent spin rotations that, in conjunction with random disorder scattering, generate spin decoherence. However, symmetries occurring under certain conditions can prevent the relaxation of particular homogeneous and inhomogeneous spin textures. The inhomogeneous spin texture, termed as persistent spin helix, is especially appealing as it enables us to manipulate the spin orientation while retaining a long spin lifetime. Recently, it was predicted that such symmetries can be realized in zinc-blende two-dimensional electron gases if at least two growth-direction Miller indices agree in modulus and the coefficients of the Rashba and linear Dresselhaus spin-orbit couplings are suitably matched [PRL 117, 236801 (2016)]. In the present paper, we systematically analyze the impact of the symmetry-breaking cubic Dresselhaus spin-orbit coupling, which generically coexists in these systems, on the stability of the emerging spin helices with respect to the growth direction. We find that, as an interplay between orientation and strength of the effective magnetic field induced by the cubic Dresselhaus terms, the spin relaxation is weakest for a low-symmetry growth direction that can be well approximated by a [225] lattice vector. These quantum wells yield a 30\% spin-helix lifetime enhancement compared to [001]-oriented electron gases and, remarkably, require a negligible Rashba coefficient. The rotation axis of the corresponding spin helix is only slightly tilted out of the quantum-well plane. This makes the experimental study of the spin-helix dynamics readily accessible for conventional optical spin orientation measurements where spins are excited and detected along the quantum-well growth direction.
- arXiv:2003.06553 [pdf, other]
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Title: Topological phase transition in layered magnetic compound MnSb2Te4: Spin-orbit coupling and interlayer coupling dependecesSubjects: Materials Science (cond-mat.mtrl-sci)
Based on the first-principles calculations and theoretical analysis, we investigate the electronic structures, topological phase transition (TPT) and topological properties of layered magnetic compound MnSb2Te4. It has the similar crystal and magnetic structure as the magnetic topological insulator MnBi2Te4. We find that when the spin-orbit coupling (SOC) is considered, the band structure of MnSb2Te4 in antiferromagnetic (AFM) state has no band inversion at {\Gamma}. This is due to the SOC strength of Sb is less than that of Bi. The band inversion can be realized by increasing the SOC of Sb by 0.3 times, which drives MnSb2Te4 from a trivial AFM insulator to an AFM topological insulator (TI) or axion insulator. Uniaxial compressive strain along the layer stacking direction is another way to control the band inversion. The interlayer distance shorten by 5% is needed to drive the similar TPT. For the ferromagnetic (FM) MnSb2Te4 with experimental crystal structure, it is a normal FM insulator. The band inversion can happen when SOC is enhanced by 0.1 times or the interlayer distance is decreased by more than 1%. Thus, FM MnSb2Te4 can be tuned to be the simplest type-I Weyl semimetal with only one pair of Weyl nodes on the three-fold rotational axis. These two Weyl nodes are projected onto (1-10) surface with one Fermi arc connecting them.
- arXiv:2003.06558 [pdf, ps, other]
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Title: Electro-osmotic properties of porous permeable filmsSubjects: Soft Condensed Matter (cond-mat.soft); Chemical Physics (physics.chem-ph)
Permeable porous coatings on a flat solid support significantly impact its electrostatic and electrokinetic properties. Existing work has focused on simplified cases, such as weakly charged and/or thick porous films, with limited theoretical guidance. Here, we consider the general case of coatings of any given volume charge density and obtain analytic formulas for electrostatic potential profiles, valid for any film thickness and salt concentration. They allow us to calculate analytically the difference between potentials at solid support and at interface with an outer electrolyte, that is the key parameter ascertaining the functionality of permeable coatings. Our analysis provides a framework for interpreting and predicting specific for porous films super-properties, from an enhanced ion absorption to a giant amplification of electro-osmotic flows. The results are relevant for hydrogel and zeolite coatings, porous carbon and ion-exchange resins, polyelectrolyte brushes, and more.
- arXiv:2003.06563 [pdf]
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Title: Complementary lateral-spin-orbit building blocks for programmable logic and in-memory computingComments: 22 pages, 4 figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Current-driven switching of nonvolatile spintronic materials and devices based on spin-orbit torques offer fast data processing speed, low power consumption, and unlimited endurance for future information processing applications. Analogous to conventional CMOS technology, it is important to develop a pair of complementary spin-orbit devices with differentiated magnetization switching senses as elementary building blocks for realizing sophisticated logic functionalities. Various attempts using external magnetic field or complicated stack/circuit designs have been proposed, however, plainer and more feasible approaches are still strongly desired. Here we show that a pair of two locally laser annealed perpendicular Pt/Co/Pt devices with opposite laser track configurations and thereby inverse field-free lateral spin-orbit torques (LSOTs) induced switching senses can be adopted as such complementary spin-orbit building blocks. By electrically programming the initial magnetization states (spin down/up) of each sample, four Boolean logic gates of AND, OR, NAND and NOR, as well as a spin-orbit half adder containing an XOR gate, were obtained. Moreover, various initialization-free, working current intensity-programmable stateful logic operations, including the material implication (IMP) gate, were also demonstrated by regarding the magnetization state as a logic input. Our complementary LSOT building blocks provide an applicable way towards future efficient spin logics and in-memory computing architectures.
- arXiv:2003.06574 [pdf, other]
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Title: Mitigating decoherence in hot electron interferometryComments: 5 pages + 3 supplemental material, 5 figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Due to their high energy, hot electrons in quantum Hall edge states can be considered as single particles that have the potential to be used for quantum optics-like experiments. Unlike photons, however, electrons typically undergo scattering processes in transport, which results in a loss of coherence and limits their ability to show true quantum behaviour. Here we study the decoherence of hot electrons in a Mach-Zehnder interferometer, and show that by optimising experimental parameters and employing energy filtration it is possible to minimise decoherence and achieve visibilities over $95\%$ in an interferometer with $10\mu$m arms. This represents a significant improvement over Fermi-level electron quantum optics, and proposes hot-electron charge pumps as an ideal platform for realising coherent nanoelectronic devices.
- arXiv:2003.06575 [pdf, ps, other]
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Title: Zero-energy modes, fractional fermion numbers and the index theorem in a vortex-Dirac fermion systemAuthors: Takashi YanagisawaComments: 8 pagesJournal-ref: Symmetry 12, 373 (2020)Subjects: High Energy Physics - Theory (hep-th); Superconductivity (cond-mat.supr-con)
Physics of topological materials have attracted much attention from both physicists and mathematicians recently. The index and the fermion number of Dirac fermions play an important role in topological insulators and topological superconductors. A zero-energy mode exists when Dirac fermions couple to objects with soliton-like structure such as kinks, vortices, monopoles, strings and branes. We discuss a system of Dirac fermions interacting with a vortex and a kink. This kind of systems will be realized on the surface of topological insulators where Dirac fermions exist. The fermion number is fractionalized and this is related to the presence of fermion zero-energy excitation modes. A zero-energy mode can be regarded as a Majorana fermion mode when the chemical potential vanishes. Our discussion includes the case where there is a half-flux quantum vortex associated with a kink in a magnetic field in a bilayer superconductor. A normalizable wave function of fermion zero-energy mode does not exist in the core of the half-flux quantum vortex. The index of Dirac operator and the fermion number have additional contributions when a soliton scalar field has a singularity.
- arXiv:2003.06597 [pdf, other]
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Title: On the periodicity of superconducting shape resonances in thin filmsComments: 7 pages, 6 figuresSubjects: Superconductivity (cond-mat.supr-con)
The pairing temperature of superconducting thin films is expected to display, within the Bardeen--Cooper--Schrieffer theory, oscillations as a function of the film thickness. We show that the pattern of these oscillations switches between two different periodicities at a density-dependent value of the superconducting coupling. The transition is most abrupt in the anti-adiabatic regime, where the Fermi energy is less than the Debye energy. To support our numerical data, we provide new analytical expressions for the chemical potential and the pairing temperature as a function of thickness, which only differ from the exact solution at weak coupling by exponentially-small corrections.
- arXiv:2003.06601 [pdf, other]
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Title: Lattice protein design using Bayesian learningComments: 9 pages, 8 figuresSubjects: Biological Physics (physics.bio-ph); Statistical Mechanics (cond-mat.stat-mech); Machine Learning (cs.LG); Chemical Physics (physics.chem-ph)
A novel protein design method using Bayesian learning is proposed in this work. We consider a posterior probability of amino acid sequences by taking into account water and assuming a prior of sequences. For some instances of a target conformation of a two-dimensional (2D) lattice Hydrophobic-Polar (HP) model, our method successfully finds an amino acid sequence for which the target conformation has a unique ground state. However, the performance was not as good for 3D lattice HP models compared with 2D models. Furthermore, we find a strong linearity between the chemical potential of water and the number of surface residues, thereby revealing the relationship between protein structure and the effect of water molecules. The advantage of our method is that it greatly reduces computation time, because it does not require long calculations for the partition function corresponding to an exhaustive conformational search. As our method uses a general form of Bayesian learning and statistical mechanics and is not limited to lattice HP proteins, the results presented here elucidate some heuristics used successfully in previous protein design methods.
- arXiv:2003.06607 [pdf, other]
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Title: Universal finite-time thermodynamics of many-body quantum machines from Kibble-Zurek scalingComments: 10 pages, 6 figuresSubjects: Quantum Physics (quant-ph); Statistical Mechanics (cond-mat.stat-mech)
We demonstrate the existence of universal features in the finite-time thermodynamics of quantum machines by considering a many-body quantum Otto cycle in which the working medium is driven across quantum critical points during the unitary strokes. Specifically, we consider a quantum engine powered by dissipative energizing and relaxing baths. We show that under very generic conditions, the output work is governed by the Kibble-Zurek mechanism, i.e., it exhibits a universal power-law scaling with the driving speed through the critical points. We also optimize the finite-time thermodynamics as a function of the driving speed. The maximum power and the corresponding efficiency take a universal form, and are reached for an optimal speed that is governed by the critical exponents. We exemplify our results by considering a transverse Ising spin chain as the working medium. For this model, we also study how engine parameters like efficiency and power vary as the engine becomes critical.
- arXiv:2003.06608 [pdf, other]
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Title: Diffusion quantum Monte Carlo and GW study of the electronic properties of monolayer and bulk hexagonal boron nitrideJournal-ref: Phys. Rev. B 101, 205115 (2020)Subjects: Materials Science (cond-mat.mtrl-sci)
We report diffusion quantum Monte Carlo (DMC) and many-body $GW$ calculations of the electronic band gaps of monolayer and bulk hexagonal boron nitride (hBN). We find the monolayer band gap to be indirect. $GW$ predicts much smaller quasiparticle gaps at both the single-shot $G_0W_0$ and the partially self-consistent $GW_0$ levels. In contrast, solving the Bethe-Salpeter equation on top of the $GW_0$ calculation yields an exciton binding energy for the direct exciton at the $K$ point in close agreement with the DMC value. Vibrational renormalization of the electronic band gap is found to be significant in both the monolayer and the bulk. Taking vibrational effects into account, DMC overestimates the band gap of bulk hBN, while $GW$ theory underestimates it.
- arXiv:2003.06609 [pdf]
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Title: Field induced single molecule magnet behavior in Dy-based coordination polymerComments: 4 pages, 3 figuresSubjects: Materials Science (cond-mat.mtrl-sci); Strongly Correlated Electrons (cond-mat.str-el)
A new mononuclear Dysprosium based Coordination Polymer {Dy-CP} was investigated magnetically using dc and ac magnetic susceptibility. The dc magnetic susceptibility does not exhibit any long-range ordering down to 1.8 K and the negative value of Curie Constant (~ - 4 K) indicate the dominance of antiferromagnetic interactions between the Dy (III) spins. Ac susceptibility exhibits absence of single molecular magnet behavior at zero dc magnetic field and shows signal of quantum tunneling magnetization (QTM) below 8 K. However, on the superimposition of dc magnetic field (3 kOe), frequency dependent relaxation peak emerged at T_f = 5 K and QTM signal suppress at higher fields. The intermediate value of Mydosh parameter calculated from the shift in peak position (T_f) in ac susceptibility reflects the formation of superparamagnetic state. Further, the temperature dependence of Tf is analyzed with Arrhenius and Cole-Cole plot. The magnetic susceptibility analysis yields characteristics pre-relaxation factor 1.40x10^(-12) sec and energy barrier {\Delta}E/k_B = 93.4 K, indicating the slow spin relaxation. The Cole-Cole fit to the ac susceptibility data shows further evidence for the single ion spin relaxation. Thus, the magnetic measurements support the single-molecule magnet behavior in Dy-CP under the application of dc magnetic field.
- arXiv:2003.06619 [pdf, other]
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Title: Optical signatures of shear collective modes in strongly interacting Fermi liquidsAuthors: D. ValentinisComments: 44 pages, 20 figuresSubjects: Strongly Correlated Electrons (cond-mat.str-el)
The concept of Fermi liquid lays a solid cornerstone to the understanding of electronic correlations in quantum matter. This ordered many-body state, entailed by the Pauli exclusion principle, rigorously organizes electrons at zero temperature in progressively higher momentum states, up to the Fermi surface. As such, it displays rigidity against perturbations, with consequences like Fermi-surface resonances manifesting themselves in longitudinal and transverse collective modes, as observed in liquid helium. However, the quest for understanding and probing Fermi-liquid collective modes in charged solid-state systems remains a challenge. In this paper I analyze the transverse shear response of neutral and charged three-dimensional Fermi liquids as a function of temperature, excitation frequency and momentum, for interactions expressed in terms of the first symmetric Landau parameter. I consider the effect of momentum-conserving quasiparticle collisions and momentum-relaxing scattering in relaxation-time approximation on the coupling between photons and Fermi-surface collective modes, thus deriving the Fermi-liquid optical conductivity and dielectric function. In the high-frequency, long-wavelength excitation regime the electrodynamic response entails two coherent and frequency-degenerate polaritons, and its spatial nonlocality is encoded by a frequency- and interaction-dependent Fermi-liquid generalized shear modulus; in the opposite high-momentum low-frequency regime anomalous skin effect takes place. I identify observable signatures of propagating shear collective modes in optical spectroscopy experiments, with applications to the surface impedance and the optical transmission of thin films.
- arXiv:2003.06625 [pdf]
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Title: Prediction of the Reactivity of Argon with Xenon under High PressureComments: 11 pages, 5 figuresJournal-ref: ACS Omega 4, 13640 (2019)Subjects: Materials Science (cond-mat.mtrl-sci); Chemical Physics (physics.chem-ph); Computational Physics (physics.comp-ph)
Pressure significantly modifies the microscopic interactions in condense phase, leading to new patterns of bonding and unconventional chemistry. Both argon and xenon possess closed-shell electronic structures, which renders them chemically unreactive. Using unbiased structure searching techniques combined with first-principles calculations, we demonstrate the reaction of argon with xenon at a pressure as low as 1.1 GPa, producing a novel van der Waals compound XeAr2, which crystallizes in the MgCu2-type Laves phase structure. Due to the pressure-induced delocalization of the electrons in outermost shells, the covalent Xe-Xe and Xe-Ar bonds have been detected which lead XeAr2 to be unexpectedly stable without any phase transition or decomposition at least up to 500 GPa.
- arXiv:2003.06626 [pdf]
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Title: Orbital localization error of density functional theory in shear properties of vanadium and niobiumComments: 27 pages, 5 figures, with Supplementary MaterialJournal-ref: J. Chem. Phys. 152, 024118 (2020)Subjects: Materials Science (cond-mat.mtrl-sci); Computational Physics (physics.comp-ph); Quantum Physics (quant-ph)
It is believed that the density functional theory (DFT) describes most elements with s, p and d orbitals very well, except some materials that having strongly localized and correlated valence electrons. In this work, we find that the widely employed exchange-correlation (xc) functionals, including LDA, GGA and meta-GGA, underestimate the shear modulus and phase stability of V and Nb greatly. The advanced hybrid functional that is usually better for correlated system, on the other hand, completely fails in these two simple metals. This striking failure is revealed due to the orbital localization error in GGA, which is further deteriorated by hybrid functionals. This observation is corroborated by a similar failure of DFT+U and van der Waals functionals when applied to V and Nb. To remedy this problem, an semi-empirical approach of DFT+J is proposed which can delocalize electrons by facilitating the on-site exchange. Furthermore, it is observed that including density derivatives slightly improves the performance of the semi-local functionals, with meta-GGA outperforms GGA, and the latter is better than LDA. This discovery indicates the possibility and necessity to include higher-order density derivatives beyond the Laplacian level for the purpose to remove the orbital localization error (mainly from d orbitals) and delocalization error (mainly from s and p orbitals) completely in V and Nb, so that to achieve a better description of their electronic structures. The same strategy can be applied to other d electron system and f electron system.
- arXiv:2003.06629 [pdf]
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Title: Thermodynamic anomalies and three distinct liquid-liquid transitions in warm dense liquid hydrogenComments: 34 pages, 7 figures, with Supplementary MaterialJournal-ref: Physical Review B 100, 134109 (2019)Subjects: Materials Science (cond-mat.mtrl-sci); Earth and Planetary Astrophysics (astro-ph.EP); Computational Physics (physics.comp-ph)
The properties of hydrogen at high pressure have wide implications in astrophysics and high-pressure physics. Its phase change in the liquid is variously described as a metallization, H2-dissociation, density discontinuity or plasma phase transition. It has been tacitly assumed that these phenomena coincide at a first-order liquid-liquid transition (LLT). In this work, the relevant pressure-temperature conditions are thoroughly explored with first-principles molecular dynamics. We show there is a large dependency on exchange-correlation functional and significant finite size effects. We use hysteresis in a number of measurable quantities to demonstrate a first-order transition up to a critical point, above which molecular and atomic liquids are indistinguishable. At higher temperature beyond the critical point, H2-dissociation becomes a smooth cross-over in the supercritical region that can be modelled by a pseudo-transition, where the H2-2H transformation is localized and does not cause a density discontinuity at metallization. Thermodynamic anomalies and counter-intuitive transport behavior of protons are also discovered even far beyond the critical point, making this dissociative transition highly relevant to the interior dynamics of Jovian planets. Below the critical point, simulation also reveals a dynamic H2-2H chemical equilibrium with rapid interconversion, showing that H2 and H are miscible. The predicted critical temperature lies well below the ionization temperature. Our calculations unequivocally demonstrate that there are three distinct regimes in the liquid-liquid transition of warm dense hydrogen.
- arXiv:2003.06638 [pdf, other]
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Title: Bose-Einstein-like Condensation due to Diffusivity Edge under Periodic ConfinementComments: 13 pages, 3 figures. Comments welcomeSubjects: Statistical Mechanics (cond-mat.stat-mech); Soft Condensed Matter (cond-mat.soft)
A generic class of scalar active matter, characterized at the mean field level by the diffusivity vanishing above some threshold density, was recently introduced [Golestanian R 2019 Phys. Rev. E 100 010601(R)]. In the presence of harmonic confinement, such 'diffusivity edge' was shown to lead to condensation in the ground state, with the associated transition exhibiting formal similarities with Bose-Einstein condensation (BEC). In this work, the effect of a diffusivity edge is addressed in a periodic potential in arbitrary dimensions, where the system exhibits coexistence between many condensates. Using a generalized thermodynamic description of the system, it is found that the overall phenomenology of BEC holds even for finite energy barriers separating each neighbouring pair of condensates. Shallow potentials are shown to quantitatively affect the transition, and introduce non-universality in the values of the scaling exponents.
- arXiv:2003.06641 [pdf, other]
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Title: Hidden symmetry enforced nexus points of nodal lines in layer-stacked dielectric photonic crystalsComments: 9 pages, 4 figuresSubjects: Optics (physics.optics); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
It was demonstrated recently that the connectivities of bands emerging from zero frequency in dielectric photonic crystals are distinct from their electronic counterparts with the same space groups. We discover that, in an AB-layer-stacked photonic crystal made up of anisotropic dielectrics, the unique photonic band connectivity leads to a new kind of symmetry enforced triply degenerate points as the nexuses of two nodal rings and a Kramers-like nodal line. The emergence and intersection of the line nodes are guaranteed by a generalized 1/4-period screw rotation symmetry of Maxwell's equations. The bands with a constant $k_z$ and the iso-frequency surfaces near the nexus point both disperse as a spin-1 Dirac-like cone, giving rise to exotic transport features of light at the nexus point. We show that the spin-1 conical diffraction occurs at the nexus point which can be used to manipulate the charges of optical vortices. Our work reveals that Maxwell's equations can have hidden symmetries induced by the fractional periodicity of the material tensor components and hence paves the way to find novel topological nodal structures unique to photonic systems.
- arXiv:2003.06647 [pdf, other]
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Title: Noninteracting Electrons in a Prototypical One-Dimensional Sinusoidal PotentialAuthors: David C. JohnstonComments: 11 pages, 15 captioned figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Quantum Physics (quant-ph)
A prototypical model of a one-dimensional metallic monatomic solid containing noninteracting electrons is studied, where the argument of the cosine potential energy periodic with the lattice contains the first reciprocal lattice vector G1 = 2 pi/a, where a is the lattice constant. The time-independent Schroedinger equation can be written in reduced variables as a Mathieu equation for which numerically-exact solutions for the band structure and wave functions are obtained. The band structure has band gaps that increase with increasing amplitude q of the cosine potential. In the extended-zone scheme, the energy gaps decrease with increasing index n of the Brillouin-zone boundary ka = n pi where k is the crystal momentum of the electron. The wave functions of the band electron are derived for various combinations of k and q as complex combinations of the real Mathieu functions with even and odd parity and the normalization factor is discussed. The wave functions at the bottoms and tops of the bands are found to be real or imaginary, respectively, corresponding to standing waves at these energies. Irrespective of the wave vector k within the first Brillouin zone, the electron probability density is found to be periodic with the lattice with a relatively small variation versus position for different k values. The Fourier components of the wave functions are derived versus q, which reveal multiple reciprocal-lattice wave vector components with variable amplitudes in the wave functions unless q = 0. The magnitudes of the Fourier components are found to decrease exponentially as a power of n for n ~ 3 to 45 for ka = pi/2 and q = 2 and a precise fit is obtained to the data. Finally, the band structure is calculated from the central equation and compared to the numerically-exact band structure.
- arXiv:2003.06663 [pdf, ps, other]
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Title: On the classification of topological ordersAuthors: Theo Johnson-FreydComments: 28 pages. v2 contains small improvementsSubjects: Category Theory (math.CT); Strongly Correlated Electrons (cond-mat.str-el); Quantum Algebra (math.QA)
We axiomatize the extended operators in topological orders (possibly gravitationally anomalous, possibly with degenerate ground states) in terms of monoidal Karoubi-complete $n$-categories which are mildly dualizable and have trivial centre. Dualizability encodes the word "topological," and we take it as the definition of "multifusion $n$-category"; triviality of the centre implements the physical principle of "remote detectability." We show that such $n$-categorical algebras are Morita-invertible (in the appropriate higher Morita category), thereby identifying topological orders with anomalous fully-extended TQFTs. We identify centreless fusion $n$-categories (i.e. multifusion $n$-categories with indecomposable unit) with centreless braided fusion $(n{-}1)$-categories. We then discuss the classification in low spacetime dimension, proving in particular that all $(1{+}1)$- and $(3{+}1)$-dimensional topological orders, with arbitrary symmetry enhancement, are suitably-generalized topological sigma models. These mathematical results confirm and extend a series of conjectures and proposals by X.G. Wen et al.
- arXiv:2003.06665 [pdf, other]
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Title: Latent Geometry for Complementarity-Driven NetworksAuthors: Maksim KitsakSubjects: Physics and Society (physics.soc-ph); Statistical Mechanics (cond-mat.stat-mech); Social and Information Networks (cs.SI); Data Analysis, Statistics and Probability (physics.data-an)
Networks of interdisciplinary teams, biological interactions as well as food webs are examples of networks that are shaped by complementarity principles: connections in these networks are preferentially established between nodes with complementary properties. We propose a geometric framework for complementarity-driven networks. In doing so we first argue that traditional geometric representations, e.g., embeddings of networks into latent metric spaces, are not applicable to complementarity-driven networks due to the contradiction between the triangle inequality in latent metric spaces and the non-transitivity of complementarity. We then propose the cross-geometric representation for these complementarity-driven networks and demonstrate that this representation (i) follows naturally from the complementarity rule, (ii) is consistent with the metric property of the latent space, (iii) reproduces structural properties of real complementarity-driven networks, if the latent space is the hyperbolic disk, and (iv) allows for prediction of missing links in complementarity-driven networks with accuracy surpassing existing similarity-based methods. The proposed framework challenges social network analysis intuition and tools that are routinely applied to complementarity-driven networks and offers new avenues towards descriptive and prescriptive analysis of systems in science of science and biomedicine.
- arXiv:2003.06676 [pdf, other]
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Title: Existence and computation of generalized Wannier functions for non-periodic systems in two dimensions and higherComments: 56 pages, 14 figures. Resized pictures and added reference to works on hybrid Wannier functionsSubjects: Mathematical Physics (math-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Numerical Analysis (math.NA); Computational Physics (physics.comp-ph)
Exponentially-localized Wannier functions (ELWFs) are a basis of the Fermi projection of a material consisting of functions which decay exponentially fast away from their maxima. When the material is insulating and crystalline, conditions which guarantee existence of ELWFs in dimensions one, two, and three are well-known, and methods for constructing the ELWFs numerically are well-developed. We consider the case where the material is insulating but not necessarily crystalline, where much less is known. In one spatial dimension, Kivelson and Nenciu-Nenciu have proved ELWFs can be constructed as the eigenfunctions of a self-adjoint operator acting on the Fermi projection. In this work, we identify an assumption under which we can generalize the Kivelson-Nenciu-Nenciu result to two dimensions and higher. Under this assumption, we prove that ELWFs can be constructed as the eigenfunctions of a sequence of self-adjoint operators acting on the Fermi projection. We conjecture that the assumption we make is equivalent to vanishing of topological obstructions to the existence of ELWFs in the special case where the material is crystalline. We numerically verify that our construction yields ELWFs in various cases where our assumption holds and provide numerical evidence for our conjecture.
- arXiv:2003.06677 [pdf, other]
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Title: Electrostatic quantum dot confinement in phosphoreneAuthors: B. SzafranSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We consider states localized by electrostatic potentials in phosphorene using an atomistic tight binding approach. From the results of the tight-binding calculations of the confined states we extract effective masses for the conduction band electrons in the armchair and zigzag directions. The masses derived in this way are used for a simple single-band effective mass model which, as we find, reproduces very well the tight-binding energy spectrum in external magnetic field, the probability densities and the interaction effects. Both methods produce Wigner crystallization for the ground-state of the electron pair with the single-electron islands separated in the armchair direction already for small quantum dots.
- arXiv:2003.06681 [pdf, other]
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Title: Universal approach to quantum thermodynamics of strongly coupled systems under nonequilibrium conditions and external drivingSubjects: Statistical Mechanics (cond-mat.stat-mech)
We present an approach based on a density matrix expansion to study thermodynamic properties of a quantum system strongly coupled to two or more baths. For slow external driving of the system, we identify the adiabatic and nonadiabatic contributions to thermodynamic quantities, and we show how the first and second laws of thermodynamics are manifested in the strong coupling regime. Particularly, we show that the entropy production is positive up to second order in the driving speed. The formulation can be applied both for Bosonic and Fermionic systems, and recovers previous results for the equilibrium case (Phys. Rev. B 98, 134306 [2018]). The approach is then demonstrated for the driven resonant level model as well as the driven Anderson impurity model, where the hierarchical quantum master equation method is used to accurately simulate the nonequilibrium quantum dynamics.
- arXiv:2003.06688 [pdf]
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Title: Exceptionally large anomalous Hall effect due to anticrossing of spin-split bands in the antiferromagnetic half-Heusler compound TbPtBiAuthors: Yanglin Zhu, Bahadur Singh, Yu Wang, Cheng-Yi Huang, Wei-Chi Chiu, Baokai Wang, David Graf, Yubo Zhang, Hsin Lin, Jianwei Sun, Arun Bansil, Zhiqiang MaoSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Strongly Correlated Electrons (cond-mat.str-el)
We have investigated magnetotransport properties and the topological electronic structure of the half-Heusler compound TbPtBi. Our experiments reveal an exceptionally large anomalous Hall effect (AHE) in the canted antiferromagnetic state of TbPtBi with the anomalous Hall angle (AHA) reaching ~0.68-0.76, which is a few times larger than the previously reported record in GdPtBi. First-principles electronic structure and the associated anomalous Hall conductivity were computed in order to interpret the experimental results. Our analysis shows that the AHE in TbPtBi does not originate from the Weyl points but that it is driven by the large net Berry curvature produced by the anticrossing of spin-split bands near the Fermi level in TbPtBi.
- arXiv:2003.06690 [pdf, other]
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Title: Landau levels in strained two-dimensional photonic crystalsComments: See ancillary files for supplemental material providing detailed derivationsSubjects: Optics (physics.optics); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
The principal use of photonic crystals is to engineer the photonic density of states, which controls light-matter coupling. We theoretically show that strained 2D photonic crystals can generate artificial electromagnetic fields and highly degenerate Landau levels. Since photonic crystals are not described by tight-binding, we employ a multiscale expansion of the full wave equation. Using numerical simulations, we observe dispersive Landau levels which we show can be flattened by engineering a pseudoelectric field. Artificial fields yield a design principle for aperiodic nanophotonic systems.
- arXiv:2003.06694 [pdf, other]
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Title: Integrable Kondo problemsComments: 33 pages + appendixSubjects: High Energy Physics - Theory (hep-th); Strongly Correlated Electrons (cond-mat.str-el)
We discuss the integrability and wall-crossing properties of chiral Kondo problems, where an 1d impurity is coupled to a 2d chiral CFT and triggers a defect RG flow. We review several new and old examples inspired by constructions in four-dimensional Chern-Simons theory and by affine Gaudin models.
- arXiv:2003.06698 [pdf, other]
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Title: Potassium-intercalated bulk HfS$_2$ and HfSe$_2$: Phase stability, structure, and electronic structureAuthors: Carsten Habenicht, Jochen Simon, Manuel Richter, Roman Schuster, Martin Knupfer, Bernd BüchnerComments: 15 FiguresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We have studied potassium-intercalated bulk HfS$_2$ and HfSe$_2$ by combining transmission electron energy loss spectroscopy, angle-resolved photoemission spectroscopy and density functional theory calculations. Calculations of the formation energies and the evolution of the energies of the charge carrier plasmons as a function of the potassium content show that certain, low potassium concentrations $x$ are thermodynamically unstable. This leads to the coexistence of undoped and doped domains if the provided amount of the alkali metal is insufficient to saturate the whole crystal with the minimum thermodynamically stable potassium stoichiometry. Beyond this threshold concentration the domains disappear, while the alkali metal and charge carrier concentrations increase continuously upon further addition of potassium. At low intercalation levels, electron diffraction patterns indicate a significant degree of disorder in the crystal structure. The initial order in the out-of-plane direction is restored at high $x$ while the crystal layer thicknesses expand by 33-36%. Superstructures emerge parallel to the planes which we attribute to the distribution of the alkali metal rather than structural changes of the host materials. The in-plane lattice parameters change by not more than 1%. The introduction of potassium causes the formation of charge carrier plasmons. The observation of this semiconductor-to-metal transition is supported by calculations of the density of states (DOS) and band structures as well as angle-resolved photoemission spectroscopy. The calculated DOS hint at the presence of an almost ideal two-dimensional electron gas at the Fermi level for $x<0.6$. The plasmons exhibit quadratic momentum dispersions which is in agreement with the behavior expected for an ideal electron gas.
- arXiv:2003.06715 [pdf, ps, other]
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Title: Non-Hermitian three-dimensional two-band Hopf insulatorComments: 9 pages, 9 figures, submittedSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Other Condensed Matter (cond-mat.other)
The Hopf insulator is a three-dimensional topological insulator outside the standard classification of topological insulators. Here we consider two types of non-Hermitian Hopf insulators, one without and one with the non-Hermitian skin effect. The isolated gapless points of the Hermitian model are broadened into finite regimes in the non-Hermitian models. However, the modulus of the Hopf index remains quantized in the gapped regions. The model without the non-Hermitian skin effect allows an accurate evaluation of its generalized Hopf index and energy spectrum, showing an agreement between the gapless-regime estimations from the systems with periodic- and open- boundary conditions. Near the zero-energy plane, Fermi rings can be observed whenever the Hopf index is quantized at nonzero values, and there is a bulk-boundary correspondence between the modulus of the Hopf index and the number of Fermi rings. The other model manifests the non-Hermitian skin effect in the generalized Brillouin zone and shows the skewed profiles of the bulk states. The Hopf index and energy spectrum are shown to be sensitive to the boundary condition in the presence of the non-Hermitian skin effect.
- arXiv:2003.06720 [pdf, other]
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Title: Microscopic Theory of Onset of De-Caging and Bond Breaking Activated Dynamics in Ultra-Dense Fluids with Strong Short Range AttractionsComments: 6 pages, 4 figuresSubjects: Soft Condensed Matter (cond-mat.soft); Statistical Mechanics (cond-mat.stat-mech)
We theoretically study thermally activated elementary dynamical processes that precede full structural relaxation in ultra-dense particle liquids interacting via strong short range attractive forces. Our approach is based on a microscopic theory formulated at the particle trajectory level built on the dynamic free energy concept and an explicit treatment of how attractions control physical bonding. Mean time scales for bond breaking, the early stage of cage escape, and a fixed non-Fickian displacement are analyzed in the repulsive glass, bonded repulsive (attractive) glass, fluid, and dense gel regimes. The theory predicts a strong length-scale-dependent growth of these time scales with attractive force strength at fixed packing fraction, a much weaker slowing down with density at fixed attraction strength, and a strong decoupling of the shorter bond breaking time with the other two time scales that are controlled mainly by perturbed steric caging. All results are in good accord with simulations, and additional testable predictions are made. The classic statistical mechanical projection approximation of replacing all bare attractive and repulsive forces with a single effective force determined by pair structure incurs major errors for describing processes associated with thermally activated escape from transiently localized states.
- arXiv:2003.06738 [pdf, other]
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Title: Magnetic-field-induced tunability of spin Hamiltonians: Resonances and Efimov states in Yb$_2$Ti$_2$O$_7$Comments: 16 pages, 10 figuresSubjects: Strongly Correlated Electrons (cond-mat.str-el)
Universality is a powerful concept that arises from the divergence of a characteristic length scale. For condensed matter systems, this length scale is typically the correlation length, which diverges at critical points separating two different phases. Few-particle systems exhibit a simpler form of universality when the $s$-wave scattering length diverges. A prominent example of universal phenomena is the emergence of an infinite tower of three-body bound states obeying discrete scale invariance, known as the Efimov effect, which has been subject to extensive research in chemical, atomic, nuclear and particle physics. In principle, these universal phenomena can also emerge in the excitation spectrum of condensed matter systems, such as quantum magnets [1]. However, the limited tunability of the effective inter-particle interaction relative to the kinetic energy has precluded so far their observation. Here we demonstrate that a high degree of magnetic-field-induced tunability can also be achieved in quantum magnets with strong spin-orbit coupling: a two-magnon resonance condition can be achieved in Yb$_2$Ti$_2$O$_7$ with a field of $\sim$ 13 T along the [110] direction, which leads to the formation of Efimov states in the three-magnon spectrum of this material. Raman scattering experiments can reveal the field-induced two-magnon resonance, as well as the Efimov three-magnon bound states that emerge near the resonance condition.
- arXiv:2003.06776 [pdf, ps, other]
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Title: Stability of two-dimensional asymmetric materials with a quadratic band crossing point under four-fermion interaction and impurity scatteringComments: 18 pages, 16 figuresSubjects: Strongly Correlated Electrons (cond-mat.str-el); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We investigate the impacts of combination of fermion-fermion interactions and impurity scatterings on the low-energy stabilities of two-dimensional asymmetric materials with a quadratic band crossing point by virtue of the renormalization group that allows to treat distinct sorts of physical ingredients on the same footing. The coupled flow evolutions of all interaction parameters which carry the central physical information are derived by taking into account one-loop corrections. Several intriguing results are manifestly extracted from these entangled evolutions. At first, we realize that the quadratic band touching structure is particularly robust once the fermionic couplings flow towards the Gaussian fixed point. Otherwise, it can either be stable or broken down against the impurity scattering in the vicinity of nontrivial fixed points. In addition, we figure out two parameters $\eta$ and $\lambda$ that measure rotational and particle-hole asymmetries are closely energy-dependent and exhibit considerably abundant behaviors depending upon the fates of fermion-fermion couplings and different types of impurities. Moreover, as both $\eta$ and $\lambda$ can be remarkably increased or heavily reduced in the low-energy regime, asymmetric system exhibits a sensational phenomenon that transition either from rotational or particle-hole asymmetry to symmetric situation would be activated under certain restricted condition.
- arXiv:2003.06784 [pdf, ps, other]
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Title: Diffusion in inhomogeneous media with periodic microstructuresSubjects: Analysis of PDEs (math.AP); Statistical Mechanics (cond-mat.stat-mech); Mathematical Physics (math-ph)
Diffusion in inhomogeneous materials can be described by both the Fick and Fokker--Planck diffusion equations. Here, we study a mixed Fick and Fokker-Planck diffusion problem with coefficients rapidly oscillating both in space and time. We obtain macroscopic models performing the homogenization limit by means of the unfolding technique.
- arXiv:2003.06787 [pdf, other]
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Title: Coarsening in the 2D incompressible Toner-Tu equation: Signatures of turbulenceComments: Main text: 5 pages, 4 figures. Supplemental Material: 4 pages, 6 figuresSubjects: Fluid Dynamics (physics.flu-dyn); Soft Condensed Matter (cond-mat.soft)
We investigate coarsening dynamics in the two-dimensional (2D), incompressible Toner-Tu equation. We show that coarsening proceeds via a vortex merger events, and the dynamics crucially depend on the Reynolds number (Re). For low Re, the coarsening process has similarities with Ginzburg-Landau dynamics. On the other hand, for high Reynolds number, coarsening shows signatures of turbulence. In particular, we show the presence of an enstrophy cascade from the inter-vortex separation scale to the dissipation scale.
- arXiv:2003.06809 [pdf, ps, other]
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Title: Diffusion properties of self-propelled particles in cellular flowsSubjects: Statistical Mechanics (cond-mat.stat-mech); Soft Condensed Matter (cond-mat.soft)
We study the dynamics of a self-propelled particle advected by a steady laminar flow. The persistent motion of the self-propelled particle is described by an active Ornstein-Uhlenbeck process. We focus on the diffusivity properties of the particle as a function of persistence time and free-diffusion coefficient, revealing non-monotonic behaviors, with the occurrence of a minimum and steep growth in the regime of large persistence time. In the latter limit, we obtain an analytical prediction for the scaling of the diffusion coefficient with the parameters of the active force. Our study sheds light on the effect of an inhomogeneous environment on the diffusion of active particles, such as living microorganisms and motile phytoplankton in fluids.
- arXiv:2003.06813 [pdf, ps, other]
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Title: Charge-based Modeling of Ultra Narrow Cylindrical Nanowire FETsComments: 5 pages, 2 figuresSubjects: Applied Physics (physics.app-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
This brief proposes an analytical approach to model the dc electrical behavior of extremely narrow cylindrical junctionless nanowire field-effect transistor (JLNW-FET). The model includes explicit expressions, taking into account the first-order perturbation theory for calculating eigenstates and corresponding wave functions obtained by the Schrodinger equation in the cylindrical coordinate. Assessment of the proposed model with technology computer-aided design (TCAD) simulations and measurement results confirms its validity for all regions of operation. This represents an essential step toward the analysis of circuits mainly biosensors based on junctionless nanowire transistors.
- arXiv:2003.06825 [pdf]
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Title: Magnetic critical behavior of the van der Waals Fe5GeTe2 crystal with near room temperature ferromagnetismAuthors: Zhengxian Li, Wei Xia, Hao Su, Zhenhai Yu, Yunpeng Fu, Leiming Chen, Xia Wang, Na Yu, Zhiqiang Zou, Yanfeng GuoComments: 22 pages, 2 tables, 6 figuresSubjects: Strongly Correlated Electrons (cond-mat.str-el)
The van der Waals ferromagnet Fe5GeTe2 has a Curie temperature TC of about 270 K, which can be raised above room temperature by tuning the Fe deficiency content. To achieve insights into its ferromagnetic exchange, we have studied the critical behavior by measuring the magnetization in bulk Fe5GeTe2 crystal around the ferromagnetic to paramagnetic phase transition. The analysis of the magnetization by employing various techniques including the modified Arrott plot, Kouvel-Fisher plot and critical isotherm analysis achieved a set of reliable critical exponents with TC = 273.7 K, beta = 0.3457, gamma = 1.40617, and delta = 5.021, suggesting a three-dimensional magnetic exchange with the distance decaying as J(r) ~ (r)$^-4.916, which is close to that of a three-dimensional Heisenberg model with long-range magnetic coupling.
- arXiv:2003.06828 [pdf, other]
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Title: Topological quantum control: Edge currents via Floquet depinning of skyrmions in the $ν= 0$ graphene quantum Hall antiferromagnetComments: 6 pages including refs, 4 figuresJournal-ref: Phys. Rev. B 101, 241403(R) (1st June 2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Statistical Mechanics (cond-mat.stat-mech); Strongly Correlated Electrons (cond-mat.str-el)
We propose a defect-to-edge topological quantum quench protocol that can efficiently inject electric charge from defect-core states into a chiral edge current of an induced Chern insulator. The initial state of the system is assumed to be a Mott insulator, with electrons bound to topological defects that are pinned by disorder. We show that a "critical quench" to a Chern insulator mass of order the Mott gap shunts charge from defects to the edge, while a second stronger quench can trap it there and boost the edge velocity, creating a controllable current. We apply this idea to a skyrmion charge in the $\nu = 0$ quantum Hall antiferromagnet in graphene, where the quench into the Chern insulator could be accomplished via Floquet driving with circularly polarized light.
- arXiv:2003.06830 [pdf, other]
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Title: Inaccessible entanglement in symmetry protected topological phasesComments: 16 pages, 7 figuresSubjects: Quantum Physics (quant-ph); Strongly Correlated Electrons (cond-mat.str-el)
We study the entanglement structure of symmetry-protected topological (SPT) phases from an operational point of view by considering entanglement distillation in the presence of symmetries. We demonstrate that non-trivial SPT phases in one-dimension necessarily contain some entanglement which is inaccessible if the symmetry is enforced. More precisely, we consider the setting of local operations and classical communication (LOCC) where the local operations commute with a global onsite symmetry group $G$, which we call $G$-LOCC, and we define the inaccessible entanglement $E_{inacc}$ as the entanglement that cannot be used for distillation under $G$-LOCC. We derive a tight bound on $E_{inacc}$ which demonstrates a direct relation between inaccessible entanglement and the SPT phase, namely $\log(D_\omega^2) \leq E_{inacc} \leq \log(|G|)$, where $D_\omega$ is the topologically protected edge mode degeneracy of the SPT phase $\omega$ with symmetry $G$. For particular phases such as the Haldane phase, $D_\omega = \sqrt{|G|}$ so the bound becomes an equality. We numerically investigate the distribution of states throughout the bound, and show that typically the region near the upper bound is highly populated, and also determine the nature of those states lying on the upper and lower bounds. We then discuss the relation of $E_{inacc}$ to string order parameters, and also the extent to which it can be used to distinguish different SPT phases of matter.
- arXiv:2003.06833 [pdf, other]
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Title: The Futility of Being Selfish -- The Impact of Selfish Routing on Uncoordinated and Optimized Transportation NetworksSubjects: Physics and Society (physics.soc-ph); Statistical Mechanics (cond-mat.stat-mech)
Optimizing traffic flow is essential for easing congestion. However, even when globally-optimal, coordinated and individualized routes are provided, users may choose alternative routes which offer lower individual costs. By analyzing the impact of selfish route-choices on performance using the cavity method, we find that a small ratio of selfish route-choices improves the global performance of uncoordinated transportation networks, but degrades the efficiency of optimized systems. Remarkably, compliant users always gain in the former and selfish users may gain in the latter, under some parameter conditions. The theoretical results are in good agreement with large-scale simulations. Iterative route-switching by a small fraction of selfish users leads to Nash equilibria close to the globally optimal routing solution. Our theoretical framework also generalizes the use of the cavity method, originally developed for the study of equilibrium states, to analyze iterative game-theoretical problems. These results shed light on the feasibility of easing congestion by route coordination when not all vehicles follow the coordinated routes.
- arXiv:2003.06835 [pdf]
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Title: New quantum phases of matter: Topological MaterialsComments: 9 pages, 4 FiguresJournal-ref: RESONANCE-JOURNAL OF SCIENCE EDUCATION 2020Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci)
In this article, we provide an overview of the basic concepts of novel topological materials. This new class of materials developed by combining the Weyl/Dirac fermionic electron states and magnetism, provide a materials-science platform to test predictions of the laws of topological physics. Owing to their dissipationless transport, these materials hold high promises for technological applications in quantum computing and spintronics devices.
- arXiv:2003.06837 [pdf, other]
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Title: $GW$ study of pressure-induced topological insulator transition in group IV-telluridesComments: 8 pages, 4 figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Strongly Correlated Electrons (cond-mat.str-el)
We calculate the electronic structure of the narrow gap semiconductors PbTe, SnTe and GeTe in the cubic phase using density functional theory (DFT) and the $G_0W_0$ method. Within DFT, we show that the band ordering obtained with a conventional semilocal exchange-correlation approximation is correct for SnTe and GeTe but wrong for PbTe. The correct band ordering at the high-symmetry point L is recovered adding $G_0W_0$ quasiparticle corrections. However, one-shot $G_0W_0$ produces artifacts in the band structure due to the wrong orbital character of the DFT single-particle states at the band edges close to L. We show that in order to correct these artifacts it is enough to consider the off-diagonal elements of the $G_0W_0$ self-energy corresponding to these states. We also investigate the pressure dependence of the band gap for these materials and the possibility of a transition from a trivial to a non-trivial topology of the band structure. For PbTe, we predict the band crossover and topological transition to occur at around 4.8 GPa. For GeTe, we estimate the topological transition to occur at 1.9 GPa in the constrained cubic phase, a pressure lower than the one of the structural phase transition from rombohedral to cubic. SnTe is a crystalline topological insulator at ambient pressure, and the transition into a trivial topology would take place under a volume expansion of approximately $10\%$.
- arXiv:2003.06847 [pdf, other]
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Title: Second sound in the BEC-BCS crossoverAuthors: Daniel Kai Hoffmann, Vijay Pal Singh, Thomas Paintner, Manuel Jäger, Wolfgang Limmer, Ludwig Mathey, Johannes Hecker DenschlagComments: 25 pages, 7 figuresSubjects: Quantum Gases (cond-mat.quant-gas); Atomic Physics (physics.atom-ph)
Second sound is an entropy wave which propagates in the superfluid component of a quantum liquid. Because it is an entropy wave, it probes the thermodynamic properties of the quantum liquid which are determined, e.g., by the interaction strength between the particles of the quantum liquid and their temperature. Here, we study second sound propagation for a large range of interaction strengths within the crossover between a Bose-Einstein condensate (BEC) and the Bardeen-Cooper-Schrieffer (BCS) superfluid. In particular, we investigate the strongly-interacting regime where currently theoretical predictions only exist in terms of an interpolation between the BEC, BCS and unitary regimes. Working with a quantum gas of ultracold fermionic $^6$Li atoms with tunable interactions, we show that the second sound speed varies only slightly in the crossover regime. We gain deeper insights into sound propagation and excitation of second sound by varying the excitation procedure which ranges from a sudden force pulse to a gentle heating pulse at the cloud center. These measurements are accompanied by classical-field simulations which help with the interpretation of the experimental data. Furthermore, we determine the spatial extension of the superfluid phase and estimate the superfluid density. In the future, this may be used to construct the so far unknown equation of state throughout the crossover.
- arXiv:2003.06853 [pdf, other]
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Title: Pairing patterns in one-dimensional spin- and mass-imbalanced Fermi gasesSubjects: Quantum Gases (cond-mat.quant-gas)
We study spin- and mass-imbalanced mixtures of spin-$\tfrac{1}{2}$ fermions interacting via an attractive contact potential in one spatial dimension. Specifically, we address the influence of unequal particle masses on the pair formation by means of the complex Langevin method. By computing the pair-correlation function and the associated pair-momentum distribution we find that inhomogeneous pairing is present for all studied spin polarizations and mass imbalances. To further characterize the pairing behavior, we analyze the density-density correlations in momentum space, the so-called shot noise, which is experimentally accessible through time-of-flight imaging. At finite spin polarization, the latter is known to show distinct maxima at momentum configurations associated with the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) instability. Besides those maxima, we find that additional features emerge in the noise correlations when mass imbalance is increased, revealing the stability of FFLO-type correlations against mass imbalance and furnishing an experimentally accessible signature to probe this type of pairing.
- arXiv:2003.06861 [pdf, ps, other]
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Title: Active matter, microreversibility, and thermodynamicsSubjects: Soft Condensed Matter (cond-mat.soft); Statistical Mechanics (cond-mat.stat-mech); Pattern Formation and Solitons (nlin.PS); Chemical Physics (physics.chem-ph)
Active matter, comprising many active agents interacting and moving in fluids or more complex environments, is a commonly occurring state of matter in biological and physical systems. By its very nature active matter systems exist in nonequilibrium states. In this paper the active agents are small Janus colloidal particles that use chemical energy provided by chemical reactions occurring on their surfaces for propulsion through a diffusiophoretic mechanism. As a result of interactions among these colloids, either directly or through fluid velocity and concentration fields, they may act collectively to form structures such as dynamic clusters. A general nonequilibrium thermodynamics framework for the description of such systems is presented that accounts for both self-diffusiophoresis and diffusiophoresis due to external concentration gradients, and is consistent with microreversibility. It predicts the existence of a reciprocal effect of diffusiophoresis back onto the reaction rate for the entire collection of colloids in the system, as well as the existence of a clustering instability that leads to nonequilibrium inhomogeneous system states.
- arXiv:2003.06900 [pdf, other]
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Title: Vacancy diffusion in multi-principal element alloys: the role of chemical disorder in the ordered latticeSubjects: Materials Science (cond-mat.mtrl-sci)
Many of the purported virtues of Multi-Principal Element Alloys (MPEAs), such as corrosion, high-temperature oxidation and irradiation resistance, are highly sensitive to vacancy diffusivity. Similarly, solute interdiffusion is governed by vacancy diffusion -- it is often unclear whether MPEAs are truly stable, or effectively stabilized by slow interdiffusion. The considerable composition space afforded to these alloys makes optimizing for desired properties a daunting task; theoretical and computational tools are necessary to guide alloy development. For diffusion, such tools depend on both a knowledge of the vacancy migration barriers within a given alloy and an understanding of how these barriers influence vacancy diffusivity. We present a generalized theory of vacancy diffusion in rugged energy landscapes, paired with Kinetic Monte Carlo simulations of MPEA vacancy diffusion. The barrier energy statistics are informed by nudged elastic band calculations in the equiatomic CoNiCrFeMn alloy. Theory and simulations show that vacancy diffusion in solid-solution MPEAs is not necessarily sluggish, but can potentially be tuned, and that trap models are an insufficient explanation for sluggish diffusion in the CoNiCrFeMn HEA. These results also show that any model that endeavors to faithfully represent diffusion-related phenomena must account for the full nature of the energy landscape, not just the migration barriers.
- arXiv:2003.06901 [pdf]
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Title: Solving constrained optimization problems without Lagrange multipliersAuthors: Cyril CayronComments: 18 pages, 10 figuresSubjects: Optimization and Control (math.OC); Materials Science (cond-mat.mtrl-sci)
Constrained optimization problems exist in many domains of science, such as thermodynamics, mechanics, economics, etc. These problems are classically solved with the help of the Lagrange multipliers and the Lagrangian function. However, the disadvantage of this approach is that it artificially increases the dimensionality of the problem. Here, we show that the determinant of the Jacobian of the problem (function to optimize and constraints) is null. This extra equation transforms any equality-constrained optimization problem into a solving problem of same dimension. We also introduced the constraint matrices as the largest square submatrices of the Jacobian of the constraints. The boundaries of the constraint domain are given by the nullity of their determinants. The constraint matrices also permit to write the function to be optimized as a Taylor series of any of its variable, with its coefficients algebraically determined by an iterative process of partial derivation.
- arXiv:2003.06904 [pdf, other]
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Title: Probing the interactions between interstitial hydrogen atoms in niobium through density functional theory calculationsSubjects: Materials Science (cond-mat.mtrl-sci)
Past experiments about hydrogen absorption in niobium have revealed specific properties about interactions between interstitial hydrogen atoms. It has been reported that there are long-range attractive and short-range repulsive interactions between interstitial hydrogen atoms in niobium. It has also been reported that these interactions are of many-body nature. While previous understanding of these interactions is based on experimental inferences from past experiments, through these calculations, for the first time, we can understand the nature of the interactions at a fundamental level. In this work, we use Density Functional Theory calculations to study the interactions of interstitial hydrogen atoms in niobium. We report here that these interactions are a combination of an attractive, indirect image interaction and a repulsive, direct interaction. Through our calculations, we also infer here that these interactions indeed have many-body characteristics.
- arXiv:2003.06905 [pdf, other]
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Title: Model of bosonization by flux attachment on hamiltonian lattices of arbitrary dimensionSubjects: Mathematical Physics (math-ph); Strongly Correlated Electrons (cond-mat.str-el); High Energy Physics - Lattice (hep-lat); High Energy Physics - Theory (hep-th)
We present and prove the correctness of a bosonization prescription for fermionic lattice models in arbitrary dimensions. Our bosonized model is subject to constraints, which are interpreted in the language of lattice $\mathbb{Z}_2$ gauge theory. Complete solutions of the constraints is found in the case of even-even spatial lattices. Further possible relations with other topologically non-trivial lattice models are discussed.
- arXiv:2003.06921 [pdf, ps, other]
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Title: Projected Gross-Pitaevskii equation for ring-shaped Bose-Einstein condensatesSubjects: Quantum Gases (cond-mat.quant-gas)
We propose an alternative implementation of the Projected Gross-Pitaevskki equation adapted for numerical modeling of the atomic Bose-Einstein condensate trapped in a toroidally-shaped potential. We present an accurate and efficient scheme to evaluate the required matrix elements and calculate time evolution of the matter wave field. We analyze the stability and accuracy of the developed method for equilibrium and nonequilibrium solutions in a ring-shaped trap with additional barrier potential corresponding to recent experimental realizations.
- arXiv:2003.06947 [pdf]
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Title: Mapping nanoscale dynamic properties of suspended and supported multi-layer graphene membranes via contact resonance and ultrasonic scanning probe microscopiesAuthors: Marta Mucientes, Robert McNair, Adrian Peasey, Shouqi Shao, Joshua Wengraf, Kunal Lulla, Benjamin J. Robinson, Oleg KolosovSubjects: Applied Physics (physics.app-ph); Materials Science (cond-mat.mtrl-sci)
Graphene (GR) remarkable mechanical and electrical properties - such as its Young's modulus, low mass per unit area, natural atomic flatness and electrical conductance - would make it an ideal material for micro and nanoelectromechanical systems (MEMS and NEMS). However, the difficulty of attaching GR to supports coupled with naturally occurring internal defects in a few-layer GR can significantly adversely affect the performance of such devices. Here, we have used a combined contact resonance atomic force microscopy (CR-AFM) and ultrasonic force microscopy (UFM) approach to characterise and map with nanoscale spatial resolution GR membrane properties inaccessible to most conventional scanning probe characterisation techniques. Using a multi-layer GR plate (membrane) suspended over a round hole we show that this combined approach allows access to the mechanical properties, internal structure and attachment geometry of the membrane providing information about both the supported and suspended regions of the system. We show that UFM allows the precise geometrical position of the supported membrane-substrate contact to be located and provides indication of the local variation of its quality in the contact areas. At the same time, we show that by mapping the position sensitive frequency and phase response of CR-AFM response, one can reliably quantify the membrane stiffness, and image the defects in the suspended area of the membrane. The phase and amplitude of experimental CR-AFM measurements show excellent agreement with an analytical model accounting for the resonance of the combined CR-AFM probe-membrane system. The combination of UFM and CR-AFM provide a beneficial combination for investigation of few-layer NEMS systems based on two dimensional materials.
- arXiv:2003.07011 [pdf]
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Title: Machine learning identifies scale-free properties in disordered materialsComments: 44 pages, 15 figuresSubjects: Optics (physics.optics); Disordered Systems and Neural Networks (cond-mat.dis-nn); Computational Physics (physics.comp-ph); Data Analysis, Statistics and Probability (physics.data-an)
The vast amount of design freedom in disordered systems expands the parameter space for signal processing, allowing for unique signal flows that are distinguished from those in regular systems. However, this large degree of freedom has hindered the deterministic design of disordered systems for target functionalities. Here, we employ a machine learning (ML) approach for predicting and designing wave-matter interactions in disordered structures, thereby identifying scale-free properties for waves. To abstract and map the features of wave behaviours and disordered structures, we develop disorder-to-localization and localization-to-disorder convolutional neural networks (CNNs). Each CNN enables the instantaneous prediction of wave localization in disordered structures and the instantaneous generation of disordered structures from given localizations. We demonstrate that CNN-generated disordered structures have scale-free properties with heavy tails and hub atoms, which exhibit an increase of multiple orders of magnitude in robustness to accidental defects, such as material or structural imperfection. Our results verify the critical role of ML network structures in determining ML-generated real-space structures, which can be used in the design of defect-immune and efficiently tunable devices.
- arXiv:2003.07022 [pdf, other]
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Title: Creation of nanometric magnetic skyrmions by global application of circularly polarized microwave magnetic fieldComments: 10 pages, 6 figures, accepted for publication in Physical Review BSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
From a theoretical perspective, we demonstrate that nanometric magnetic skyrmions are created by application of a circularly polarized microwave magnetic field to a thin-plate Dzyaloshinskii-Moriya ferromagnet with fabricated rectangular holes. This phenomenon is caused by an effective steady magnetic field perpendicular to the microwave-polarization plane induced by the rotating magnetic field and the intense interference of spin waves excited by this magnetic field due to the hole structure, which causes reversals of local magnetizations and results in the formation of skyrmions. Our proposal provides a new option to write or create magnetic textures the sizes of which are much smaller than the spot size of the external stimulus such as magnetic field, light, and microwave.
- arXiv:2003.07034 [pdf, ps, other]
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Title: Theoretical study on stabilization and destabilization of magnetic skyrmions by uniaxial-strain-induced anisotropic Dzyaloshinskii--Moriya interactionsComments: 9 pages, 5 figuresJournal-ref: Physical Review Materials 4, 034404 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Strongly Correlated Electrons (cond-mat.str-el)
Magnetic skyrmions in chiral-lattice ferromagnets are currently attracting enormous research interest because of their potential applications in spintronic devices. However, they emerge in bulk specimens only in a narrow window of temperature and magnetic field. This limited stability regime is recognized as an obstacle to technical applications. Recent experiments demonstrated that the thermodynamic stability of magnetic skyrmions is enhanced or suppressed by the application of a uniaxial strain depending on its axial direction in bulk chiral-lattice ferromagnets MnSi [Y. Nii et al., Nat. Commun. 6, 8539 (2015), A. Chacon et al., Phys. Rev. Lett. 115, 267202 (2015)] and Cu2OSeO3 [S. Seki et al., Phys. Rev. B 96, 220404(R) (2017)]. Motivated by these experimental discoveries, we theoretically investigated the effects of anisotropic Dzyaloshinskii--Moriya interactions on the stability of magnetic skyrmions caused by this uniaxial strain. We find that magnetic skyrmions are significantly stabilized (destabilized) in the presence of anisotropic DM interactions when an external magnetic field lies perpendicular (parallel) to the anisotropy axis, along which the DM coupling is strengthened. Our results account completely for the experimentally observed strain-induced stabilization and destabilization of magnetic skyrmions and provide a firm ground for possible strain engineering of skyrmion-based electronic devices.
- arXiv:2003.07038 [pdf, other]
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Title: Fractional Quantum Hall Effect at $ν=2+4/9$Comments: 14 pages, 12 figures (includes supplemental material)Subjects: Strongly Correlated Electrons (cond-mat.str-el); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Motivated by two independent experiments revealing a resistance minimum at the Landau level (LL) filling factor $\nu=2+4/9$, characteristic of fractional quantum Hall effect (FQHE) and suggesting electron condensation into a yet unknown quantum liquid, we propose that this state belongs in a parton sequence, put forth recently to understand the emergence of FQHE at $\nu=2+6/13$. While the $\nu=2+4/9$ state proposed here directly follows three simpler parton states, all known to occur in the second LL, it is topologically distinct from the Jain composite fermion (CF) state which occurs at the same $\nu=4/9$ filling of the lowest LL. We predict experimentally measurable properties of the $4/9$ parton state that can reveal its underlying topological structure and definitively distinguish it from the $4/9$ Jain CF state.
- arXiv:2003.07039 [pdf, other]
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Title: Detection of magnetic impurities using electron vortex beamsComments: 11 pages, 7figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Electron microscopy stands out as electron waves providing higher spatial resolving power compared to their optical counterpart. Here we investigate theoretically the interaction of twisted electrons generated in transmission electron microscope (TEM) and magnetic impurity, in which the magnetic dipole moment is taken as a demonstration element. In addition to the usual optical phase, the inhomogeneous vector potential generated by the magnetic dipole moment makes additional contribution to the intrinsic orbital angular momentum of electrons, resulting in a Gouy phase shift. By interfering the outgoing twisted electron beam with a reference Gaussian-cylindrical wave, one can determine the magnitude and orientation of magnetic dipole directly via the rotational and deformed interference pattern. The obtained results demonstrate the usefulness of twisted electron beams for probing the atomic- and nanoscale magnetism of impurity by TEM and the proposed model provides the conceptual basis for future developments of the TEM method.
- arXiv:2003.07047 [pdf, ps, other]
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Title: Kinetics of actin networks formation measured by time resolved particle-tracking microrheologyAuthors: Maayan Levin, Raya Sorkin, David Pine, Rony Granek, Anne Bernheim-Groswasser, Yael RoichmanComments: 15 pages 8 figuresSubjects: Soft Condensed Matter (cond-mat.soft); Materials Science (cond-mat.mtrl-sci); Biological Physics (physics.bio-ph)
Actin is one of the most studied cytoskeleton proteins showing a very rich span of structures. It can self-assemble actively into dynamical structures that govern the mechanical properties of the cell, its motility and its division. However, only very few studies characterize the kinetics of the active actin self-assembly process beyond the formation of an entangled network. Here, we follow actin polymerization kinetics and organization into entangled networks using time resolved passive microrheology. We establish a relationship between the initial concentration of monomers, the active polymerization and network formation kinetics, and the viscoelastic properties from the onset of actin polymerization upto the formation of a steady state entangled network. Surprisingly, we find that at high enough initial monomer concentrations the elastic modulus of the forming actin networks overshoots and then relaxes with a -2/5 power law, that we attribute to rearrangements of the network into a steady state structure.
- arXiv:2003.07052 [pdf, other]
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Title: Topological superconductivity in EuS/Au/superconductor heterostructuresComments: 6 pages, 3 figures. Comments are welcomeSubjects: Superconductivity (cond-mat.supr-con); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
In recent years, signatures of Majorana fermions have been demonstrated experimentally in several superconducting systems. However, finding systems which can be scaled up to accommodate a large number of Majorana fermions for quantum computation remains a major challenge for experimentalists. In a recent work [1], signatures of a pair of Majorana zero modes (MZMs) were found in a new experimental platform formed by EuS islands deposited on top of a gold wire which were made superconducting through proximity coupling to a superconductor. In this work, we provide a theoretical explanation for how MZMs can be formed in EuS/Au/superconductor heterostructures. This simple experimental setup provides a new route for realizing a large number of Majorana fermions for quantum computations.
- arXiv:2003.07056 [pdf, ps, other]
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Title: Probing the singlet-triplet splitting in double quantum dots: Implications of the ac field amplitudeComments: 10 pagesSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We consider a double quantum dot whose energy detuning is controlled by an ac electric field. We demonstrate an energy configuration for which the ac-induced current flowing through the double dot directly probes the spin-orbit anticrossing point for small ac field amplitudes. On the contrary, as the ac amplitude increases a current antiresonance is formed, and the direct information about the spin-orbit interaction is lost. This result indicates that a large ac amplitude is not necessarily advantageous for the spectroscopy of spin-orbit coupled two-spin states. Moreover, we investigate the ac-induced current peaks versus the ac amplitude and show a current suppression when the ac field forms spin blocked states. This effect gives rise to a characteristic pattern for the current which can be controlled at will by tuning the ac amplitude. Our results can be explored by performing electronic transport measurements in the spin blockade regime.
- arXiv:2003.07063 [pdf, ps, other]
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Title: Covid-19 spread: Reproduction of data and prediction using a SIR model on Euclidean networkComments: 4 pages, 3 figuresSubjects: Physics and Society (physics.soc-ph); Statistical Mechanics (cond-mat.stat-mech); Populations and Evolution (q-bio.PE)
We study the datafor the cumulative as well as daily number of cases in the Covid-19 outbreak in China. The cumulative data can be fit to an empirical form obtained from a Susceptible-Infected-Removed (SIR) model studied on an Euclidean network previously. Plotting the number of cases against the distance from the epicenter for both China and Italy, we find an approximate power law variation with an exponent $\sim 1.85$ showing strongly that the spatial dependence plays a key role, a factor included in the model. We report here that the SIR model on the Eucledean network can reproduce with a high accuracy the data for China for given parameter values, and can also predict when the epidemic, at least locally, can be expected to be over.
- arXiv:2003.07079 [pdf]
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Title: Spin orbit field in a physically defined p type MOS silicon double quantum dotAuthors: Marian Marx, Jun Yoneda, Ángel Gutiérrez Rubio, Peter Stano, Tomohiro Otsuka, Kenta Takeda, Sen Li, Yu Yamaoka, Takashi Nakajima, Akito Noiri, Daniel Loss, Tetsuo Kodera, Seigo TaruchaComments: 21 pages, 4 figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Applied Physics (physics.app-ph); Quantum Physics (quant-ph)
We experimentally and theoretically investigate the spin orbit (SO) field in a physically defined, p type metal oxide semiconductor double quantum dot in silicon. We measure the magnetic field dependence of the leakage current through the double dot in the Pauli spin blockade. A finite magnetic field lifts the blockade, with the lifting least effective when the external and SO fields are parallel. In this way, we find that the spin flip of a tunneling hole is due to a SO field pointing perpendicular to the double dot axis and almost fully out of the quantum well plane. We augment the measurements by a derivation of SO terms using group symmetric representations theory. It predicts that without in plane electric fields (a quantum well case), the SO field would be mostly within the plane, dominated by a sum of a Rashba and a Dresselhaus like term. We, therefore, interpret the observed SO field as originated in the electric fields with substantial in plane components.
- arXiv:2003.07081 [pdf, other]
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Title: Field-induced phase transitions of the Kitaev material $α$-RuCl$_3$ probed by thermal expansion and magnetostrictionAuthors: S. Gass, P. M. Cônsoli, V. Kocsis, L. T. Corredor, P. Lampen-Kelley, D. G. Mandrus, S. E. Nagler, L. Janssen, M. Vojta, B. Büchner, A. U. B. WolterComments: 6 + 8 pages, 2 + 6 figuresSubjects: Strongly Correlated Electrons (cond-mat.str-el)
High-resolution thermal expansion and magnetostriction measurements were performed on single crystals of $\alpha$-RuCl$_3$ in magnetic fields applied parallel to the Ru-Ru bonds. The length changes were measured in the direction perpendicular to the honeycomb planes. Our data show clear thermodynamic characteristics for the field-induced phase transition at the critical field $\mu_0H_{c1} = 7.8(2)$ T where the antiferromagnetic zigzag order is suppressed. At higher fields, a kink in the magnetostriction coefficient signals an additional phase transition around $\mu_0H_{c2} \approx 11$ T. The extracted Gr\"uneisen parameter shows typical hallmarks for quantum criticality near $H_{c1}$, but also displays anomalous behavior above $H_{c1}$. We compare our experimental data with linear spin-wave calculations employing a minimal Kitaev-Heisenberg model in the semiclassical limit. Most of the salient features are in agreement with each other, however, the peculiar features in the high-field region above $H_{c1}$ cannot be accounted for in our modelling and hence suggest a genuine quantum nature. We construct a phase diagram for $\alpha$-RuCl$_3$ showing two low-temperature transitions induced by an in-plane field along the Ru-Ru bonds.
- arXiv:2003.07089 [pdf, ps, other]
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Title: Exact quantization of the XXZ spin chain embedded in a topological manifoldComments: 5 pages, 3 figuresSubjects: Mathematical Physics (math-ph); Statistical Mechanics (cond-mat.stat-mech); High Energy Physics - Theory (hep-th)
A novel Bethe Ansatz scheme is proposed to deal with topological quantum integrable systems. As an example, the anti-periodic XXZ spin chain, a typical correlated many-body system embedded in a topological manifold, is examined. Conserved "momentum" and "charge" operators are constructed despite the absence of translational invariance and $U(1)$ symmetry. The ground state energy and elementary excitations are derived exactly. It is found that two intrinsic fractional (one half) zero modes exist in most of the eigenstates. The elementary excitations show quite a different picture from that in the periodic boundary case. This method can be applied to other quantum integrable models with nontrivial topology or boundary conditions.
- arXiv:2003.07093 [pdf]
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Title: AC-frequency switchable correlated transports in rare-earth perovskite nickelatesAuthors: Jikun Chen, Haifan Li, Jiaou Wang, Xinyou Ke, Binghui Ge, Jinhao Chen, Hongliang Dong, Yong Jiang, Nuofu ChenSubjects: Materials Science (cond-mat.mtrl-sci)
Whilst electron correlations were previously recognized to trigger beyond conventional direct current (DC) electronic transportations (e.g. metal-to-insulator transitions, bad metal, thermistors), their respective influences to the alternation current (AC) transport are largely overlooked. Herein, we demonstrate active regulations in the electronic functionalities of d-band correlated rare-earth nickelate (ReNiO3) thin films, by simply utilizing their electronic responses to AC-frequencies (fAC). Assisted by temperature dependent near edge X-ray absorption fine structure analysis, we discovered positive temperature dependences in Coulomb viscosity of ReNiO3 that moderates their AC impedance. Distinguished crosslinking among R(Real)-fAC measured in nearby temperatures is observed that differs to conventional oxides. It enables active adjustability in correlated transports of ReNiO3, among NTCR-, TDelta- and PTCR- thermistors, via fAC from the electronic perspective without varying materials or device structures. The TDelta-fAC relationship can be further widely adjusted via Re composition and interfacial strains. The AC-frequency sensitivity discovered in ReNiO3 brings in a new freedom to regulating and switching the device working states beyond the present semiconductor technologies. It opens a new paradigm for enriching novel electronic applications catering automatic transmission or artificial intelligence in sensing temperatures and frequencies.
- arXiv:2003.07102 [pdf, other]
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Title: Ideal circle microswimmers in crowded mediaComments: 10 pages, 7 figuresJournal-ref: Soft Matter, 2019,15, 452-461Subjects: Biological Physics (physics.bio-ph); Soft Condensed Matter (cond-mat.soft)
Microswimmers are exposed in nature to crowded environments and their transport properties depend in a subtle way on the interaction with obstacles. Here, we investigate a model for a single ideal circle swimmer exploring a two-dimensional disordered array of impenetrable obstacles. The microswimmer moves on circular orbits in the freely accessible space and follows the surface of an obstacle for a certain time upon collision. Depending on the obstacle density and the radius of the circular orbits, the microswimmer displays either long-range transport or is localized in a finite region. We show that there are transitions from two localized states to a diffusive state each driven by an underlying static percolation transition. We determine the non-equilibrium state diagram and calculate the mean-square displacements and diffusivities by computer simulations. Close to the transition lines transport becomes subdiffusive which is rationalized as a dynamic critical phenomenon.
- arXiv:2003.07143 [pdf, other]
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Title: Unconventional phases in a Haldane model of dice latticeComments: 11 pages, 12 figuresJournal-ref: Phys. Rev. B 101, 235406 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We propose a Haldane-like model of dice lattice analogous to graphene and explore its topological properties within the tight-binding formalism. The topological phase boundary of the system is identical to that of Haldane model of graphene but the phase diagram is richer than the latter due to existence of a distorted flat band. The system supports phases which have a "gapped-out" valence (conduction) band and an indirect overlap between the conduction (valence) band and the distorted flat band. The overlap of bands imparts metallic character to the system. These phases may be further divided into topologically trivial and nontrivial ones depending on the Chern number of the "gapped-out" band. The semimetallic phases exist as distinct points that are well separated from each other in the phase diagram and exhibit spin-1 Dirac-Weyl dispersion at low energies. The Chern numbers of the bands in the Chern-insulating phases are $0$ and $\pm2$. This qualifies the system to be candidate for quantum anomalous Hall effect with two chiral channels per edge. Counterpropagating edge states emanate from the flat band in certain topologically trivial phases. The system displays beating pattern in Shubnikov de Haas oscillations for unequal magnitude of mass terms in the two valleys. We show that the chemical potential and ratio of topological parameters of the system viz. Semenoff mass and next-neighbor hopping amplitude may be experimentally determined from the number of oscillations between the beating nodes and the beat frequency, respectively.
- arXiv:2003.07147 [pdf, other]
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Title: Skyrmion Interactions and Lattices in Solvable Chiral MagnetsComments: 18 pages, 8 figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); High Energy Physics - Theory (hep-th)
We study two-body interactions of magnetic skyrmions on the plane and apply them to a (mostly) analytic description of a skyrmion lattice. This is done in the context of the solvable line, a particular choice of a potential for magnetic anisotropy and Zeeman terms, where analytic expressions for skyrmions are available. Along the solvable line the interaction energy for a pair of skyrmions is repulsive with power law fall off in contrast to the exponential decay found when the potential consists of just a Zeeman term. Using the interaction energy expressions we construct an inhomogeneous skyrmion lattice state, which is a candidate ground states for the model in particular parameter regions. We also study the instability of the ferromagnetic phase and find the phase boundary between the ferromagnetic and lattice phases. Finally we estimate the transition between the skyrmion lattice and an inhomogeneous spiral state.
- arXiv:2003.07151 [pdf, ps, other]
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Title: Enhancing spin-phonon and spin-spin interactions using linear resources in a hybrid quantum systemComments: 7 + 11 pages, and 5 + 9 figuresSubjects: Quantum Physics (quant-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Hybrid spin-mechanical setups offer a versatile platform for quantum science and technology, but improving the spin-phonon as well as the spin-spin couplings of such systems remains a crucial challenge. Here, we propose and analyze an experimentally feasible and simple method for exponentially enhancing the spin-phonon, and the phonon-mediated spin-spin interactions in a hybrid spin-mechanical setup, using only \emph{ linear resources}. Through modulating the spring constant of the mechanical cantilever with a time-dependent pump, we can acquire a tunable and nonlinear (two-phonon) drive to the mechanical mode, thus amplifying the mechanical zero-point fluctuations and directly enhancing the spin-phonon coupling. Our method allows the spin-mechanical system to be driven from the weak-coupling regime to the strong-coupling regime, and even the ultrastrong coupling regime. In the dispersive regime, this method gives rise to a large enhancement of the phonon-mediated spin-spin interaction between distant solid-state spins, typically\emph{two orders of magnitude larger} than that without modulation. As an example, we show that the proposed scheme can apply to generating entangled states of multiple spins with high fidelities even in the presence of large dissipations.
- arXiv:2003.07152 [pdf, other]
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Title: Transport and tumbling of polymers in viscoelastic shear flowSubjects: Statistical Mechanics (cond-mat.stat-mech); Soft Condensed Matter (cond-mat.soft)
Polymers in shear flow are ubiquitous and we study their motion in a viscoelastic fluid under shear. Employing dumbbells as representative, we find that the center of mass motion follows: $\langle x^2_c(t) \rangle \sim \dot{\gamma}^2 t^{\alpha+2}, ~0< \alpha <1$, generalizing the earlier result: $\langle x^2_c(t) \rangle \sim \dot{\gamma}^2t^3 ~(\alpha = 1)$. Motion of the relative coordinate, on the other hand, is quite intriguing in that $\langle x^2_r(t) \rangle \sim t^\beta$ with $\beta = 2(1-\alpha)$ for small $\alpha$. This implies nonexistence of the steady state. We remedy this pathology by introducing a nonlinear spring with FENE-LJ interaction and study tumbling dynamics of the dumbbell. The overall effect of viscoelasticity is to slow down the dynamics in the experimentally observed ranges of the Weissenberg number. We numerically obtain the characteristic time of tumbling and show that small changes in $\alpha$ result in large changes in tumbling times.
- arXiv:2003.07155 [pdf, ps, other]
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Title: Application of the diffusion equation to prove scaling invariance on the transition from limited to unlimited diffusionSubjects: Chaotic Dynamics (nlin.CD); Statistical Mechanics (cond-mat.stat-mech); Applied Physics (physics.app-ph)
The scaling invariance for chaotic orbits near a transition from unlimited to limited diffusion in a dissipative standard mapping is explained via the analytical solution of the diffusion equation. It gives the probability of observing a particle with a specific action at a given time. We show the diffusion coefficient varies slowly with the time and is responsible to suppress the unlimited diffusion. The momenta of the probability are determined and the behavior of the average squared action is obtained. The limits of small and large time recover the results known in the literature from the phenomenological approach and, as a bonus, a scaling for intermediate time is obtained as dependent on the initial action. The formalism presented is robust enough and can be applied in a variety of other systems including time dependent billiards near a transition from limited to unlimited Fermi acceleration as we show at the end of the letter and in many other systems under the presence of dissipation as well as near a transition from integrability to non integrability.
- arXiv:2003.07156 [pdf, other]
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Title: Exact results on diffusion in a piecewise linear potential with a rectangular sinkSubjects: Statistical Mechanics (cond-mat.stat-mech); Other Condensed Matter (cond-mat.other)
We propose a new method for finding the exact analytical solution in Laplace domain for the problem where the probability density of a random walker in a piece-wise linear potential in presence of a rectangular sink of arbitrary width and height. The motion of the random walker is modelled by using Smoluchowski equation. For our model we have derived exact analytical expression for rate constants. This is the first model where the exact analytical solution in closed form is possible in the case of a sink of arbitrary width for position dependent potential. This model is better for understanding reaction-diffusion systems than all other existing models available in literature.
- arXiv:2003.07157 [pdf, ps, other]
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Title: Stirling engine operating at low temperature differenceAuthors: Alejandro RomanelliComments: 16 pages, 7 figuresJournal-ref: American Journal of Physics, Vol. 88, Issue 4, 2020-03-20Subjects: Statistical Mechanics (cond-mat.stat-mech)
The paper develops the dynamics and thermodynamics of Stirling engines that run with temperature differences below 100 0C. The working gas pressure is analytically expressed using an alternative thermodynamic cycle. The shaft dynamics is studied using its rotational equation of motion. It is found that the initial volumes of the cold and hot working gas play a non-negligible role in the functioning of the engine.
- arXiv:2003.07171 [pdf, ps, other]
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Title: Unified framework for generalized quantum statistics: canonical partition function, maximum occupation number, and permutation phase of wave functionSubjects: Statistical Mechanics (cond-mat.stat-mech)
Beyond Bose and Fermi statistics, there still exist various kinds of generalized quantum statistics. Two ways to approach generalized quantum statistics: (1) in quantum mechanics, generalize the permutation symmetry of the wave function and (2) in statistical mechanics, generalize the maximum occupation number of quantum statistics. The connection between these two approaches, however, is obscure. In this paper, we suggest a unified framework to describe various kinds of generalized quantum statistics. We first provide a general formula of canonical partition functions of ideal $N$-particle gases obeying various kinds of generalized quantum statistics. Then we reveal the connection between the permutation phase of the wave function and the maximum occupation number, through constructing a method to obtain the permutation phase and the maximum occupation number from the canonical partition function. In our scheme, the permutation phase of wave functions is generalized to a matrix phase, rather than a number. It is commonly accepted that different kinds of statistics are distinguished by the maximum number. We show that the maximum occupation number is not sufficient to distinguish different kinds of generalized quantum statistics. As examples, we discuss a series of generalized quantum statistics in the unified framework, giving the corresponding canonical partition functions, maximum occupation numbers, and the permutation phase of wave functions. Especially, we propose three new kinds of generalized quantum statistics which seem to be the missing pieces in the puzzle. The mathematical basis of the scheme are the mathematical theory of the invariant matrix, the Schur-Weyl duality, the symmetric function, and the representation theory of the permutation group and the unitary group. The result in this paper builds a bridge between the statistical mechanics and such mathematical theories.
- arXiv:2003.07178 [pdf, other]
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Title: Width dependent auto-oscillating properties of constriction based spin Hall nano-oscillatorsSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Applied Physics (physics.app-ph)
We study the current tunable microwave signal properties of nano-constriction based spin Hall nano-oscillators (SHNOs) in oblique magnetic fields as a function of the nano-constriction width, $w=$~50--140 nm. The threshold current is found to scale linearly with $w$, defining a constant threshold current density of $J_{th}=$ 1.7 $\times$ 10$^{8}$ A/cm$^2$. While the current dependence of the microwave frequency shows the same generic non-monotonic behavior for all $w\geqslant$ 80 nm, the quality of the generated microwave signal improves strongly with $w$, showing a linear $w$ dependence for both the total power and the linewidth. As a consequence, the peak power for a 140 nm nano-constriction is about an order of magnitude higher than that of a 80 nm nano-constriction. The smallest nano-constriction, $w=$ 50 nm, exhibits a different behavior with a higher power and a worse linewidth indicating a crossover into a qualitatively different narrow-constriction regime.
- arXiv:2003.07179 [pdf, other]
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Title: Dark state localization of quantum emitters in a cavityAuthors: Thomas Botzung, David Hagenmüller, Stefan Schütz, Jérôme Dubail, Guido Pupillo, Johannes SchachenmayerSubjects: Quantum Physics (quant-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Quantum Gases (cond-mat.quant-gas)
We study a disordered ensemble of quantum emitters collectively coupled to a lossless cavity mode. The latter is found to modify the localization properties of the "dark" eigenstates, which exhibit a novel character of being localized on multiple, non-contiguous sites. We denote such states as semi-localized and characterize them by means of standard localization measures. We show that those states can very efficiently contribute to coherent energy transport. Our work underlines the important role of dark states in systems with strong light-matter coupling.
- arXiv:2003.07181 [pdf]
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Title: Signature of band inversion in the perovskite thin-film alloys BaSn$_{1-x}$Pb$_x$O$_3$Authors: Junichi Shiogai, Takumaru Chida, Kenichiro Hashimoto, Kohei Fujiwara, Takahiko Sasaki, Atsushi TsukazakiComments: 19 pages, 4 figuresSubjects: Materials Science (cond-mat.mtrl-sci); Strongly Correlated Electrons (cond-mat.str-el)
Perovskite oxides ABO$_3$ containing heavy B-site elements are a class of candidate materials to host topological metals with a large spin-orbit interaction. In contrast to the band insulator BaSnO$_3$, the semimetal BaPbO$_3$ is proposed to be a typical example with an inverted band structure, the conduction band of which is composed of mainly the O-2p orbital. In this study, we exemplify a band-gap modification by systematic structural, optical, and transport measurements in BaSn$_{1-x}$Pb$_x$O$_3$ films. A sudden suppression of the conductivity and an enhancement of the weak antilocalization effect at $x$ = 0.9 indicate the presence of a singular point in the electronic structure as a signature of the band inversion. Our findings provide an intriguing platform for combining topological aspects and electron correlation in perovskite oxides based on band-gap engineering.
- arXiv:2003.07196 [pdf, other]
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Title: The Josephson Effect RevisitedComments: 6 pages, 8 figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
The radio-frequency (RF) signal, observed in a Josephson junction, is shown to stem from bound electrons, tunneling periodically through the insulating film. This holds also for the microwave mediated tunneling. The Josephson effect is found to be conditioned by the same prerequisite worked out previously for persistent currents and thermal equilibrium. The observed negative resistance behaviour turns out to be unrelated to the Josephson effect and originates from the properties of the superconducting current, flowing through the Josephson junction.
- arXiv:2003.07211 [pdf, ps, other]
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Title: Anomalous 2D-confined electronic transport in layered organic charge-glass systemsComments: 5 pages, 4 figuresSubjects: Strongly Correlated Electrons (cond-mat.str-el)
To get insight into the nature of the electronic fluid in the frustration-driven charge glasses, we investigate in-plane and out-of-plane charge transport for several quasi-triangular-lattice organic systems, $\theta$-(BEDT-TTF)$_2$X [X=RbZn(SCN)$_4$, CsZn(SCN)$_4$ and I$_3$]. These compounds host a charge order, charge glass and Fermi liquid, depending on the strength of charge frustration. We find that the resistivity exhibits extremely two-dimensional (2D) anisotropy and contrasting temperature dependence between in the in-plane and out-of-plane directions in the charge glass phase, qualitatively distinguished from the charge order and metallic states. The experimental features indicate that the frustration-induced charge glass carries an anomalous 2D-confined electronic fluid with possible charge excitations other than conventional quasiparticles.
- arXiv:2003.07213 [pdf]
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Title: Observation of a three-dimensional fractional Hall response in HfTe5Authors: S. Galeski, X. Zhao, R. Wawrzyńczak, T. Meng, T. Förster, S. Honnali, N. Lamba, T. Ehmcke, A. Markou, W. Zhu, J. Wosnitza, C. Felser, G. F. Chen, J. GoothComments: 35 pages with 17 figuresSubjects: Strongly Correlated Electrons (cond-mat.str-el); Materials Science (cond-mat.mtrl-sci)
Interacting electrons in two dimensions can bind magnetic flux lines to form composite quasiparticles with fractional electric charge, manifesting themselves in the fractional quantum Hall effect (FQHE). Although the FQHE has also been predicted to occur in three dimensions, it has not yet been experimentally observed. Here, we report the observation of fractional plateaus in the Hall conductivity of the bulk semimetal HfTe5 at magnetic fields beyond the quantum limit. The plateaus are accompanied by Shubnikov-de Haas minima of the longitudinal electrical resistivity. The height of the Hall plateaus is given by twice the Fermi wave vector in the direction of the applied magnetic field and scales with integer and particular fractional multiples of the conductance quantum. Our findings are consistent with strong electron-electron interactions, stabilizing a fractionalized variant of the Hall effect in three dimensions.
- arXiv:2003.07215 [pdf, other]
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Title: Chiral anomalies induced transport in Weyl semimetals in quantizing magnetic fieldComments: 11 pages, 8 figures, Comments are welcomeSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Weyl semimetals host relativistic chiral quasiparticles, which display quantum anomalies in the presence of external electromagnetic fields. Here, we study the manifestations of chiral anomalies in the longitudinal and planar magneto-transport coefficients of Weyl semimetals, in the presence of a quantizing magnetic field. We present a general framework for calculating all the transport coefficients in the regime where multiple Landau levels are occupied. We explicitly show that all the longitudinal and planar transport coefficients show Shubnikov-de Haas like quantum oscillations which are periodic in 1/B. Our calculations recover the quadratic-B dependence in the semiclassical regime, and predict a linear-B dependence in the ultra-quantum limit for all the transport coefficients.
- arXiv:2003.07217 [pdf, other]
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Title: A novel class of translationally invariant spin chains with long-range interactionsComments: Typeset in LaTeX, 37 pages, 4 figuresSubjects: Statistical Mechanics (cond-mat.stat-mech); High Energy Physics - Theory (hep-th); Mathematical Physics (math-ph); Exactly Solvable and Integrable Systems (nlin.SI)
We introduce a new class of open, translationally invariant spin chains with long-range interactions depending on both spin permutation and polarized spin reversal operators, which includes the Haldane-Shastry chain as a degenerate case. The new class is characterized by the fact that the Hamiltonian is invariant under "twisted" translations, combining an ordinary translation with a spin flip at one end of the chain. When the spin-spin interactions depend on the inverse square of the distance, we are able to compute in closed form the model's partition function and hence study several statistical properties of its spectrum. In particular, we show that this model possesses a highly degenerate spectrum, which suggests the existence of an underlying twisted Yangian symmetry.
- arXiv:2003.07236 [pdf, other]
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Title: Analysis of a fourth order exponential PDE arising from a crystal surface jump process with Metropolis-type transition ratesComments: 21 pages, 5 figures, comments welcome!Subjects: Analysis of PDEs (math.AP); Materials Science (cond-mat.mtrl-sci); Statistical Mechanics (cond-mat.stat-mech)
We analytically study a fourth order PDE modeling rough crystal surface diffusion on the macroscopic level. The PDE, originally derived by the second author, is the continuum limit of a microscopic model of the surface dynamics, specified as a Markov jump process with Metropolis type transition rates. We discuss existence of solutions globally in time and long time dynamics for the PDE model. We also outline the derivation of the PDE from the microscopic dynamics, connecting it with previous derivations for dynamics in which the transition rates relate to bond-breaking. In addition, we provide numerical evidence for the convergence to the PDE from the microscopic model as well as numerical studies of the dynamics of the PDE model itself.
- arXiv:2003.07245 [pdf, other]
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Title: Stability analysis of charge-controlled soft dielectric platesSubjects: Soft Condensed Matter (cond-mat.soft)
We examine the stability of a soft dielectric plate deformed by the coupled effects of a mechanical pre-stress applied on its lateral faces and an electric field applied through its thickness under charge control. The electric field is created by spraying charges on the major faces of the plate: although in practice this mode of actuation is harder to achieve than a voltage-driven deformation, here we find that it turns out to be much more stable in theory and in simulations.
First we show that the electromechanical instability based on the Hessian criterion associated with the free energy of the system does not occur at all for charge-driven dielectrics for which the electric displacement is linear in the electric field. Then we show that the geometric instability associated with the formation of small-amplitude wrinkles on the faces of the plate that arises under voltage control does not occur either under charge control. This is in complete contrast to voltage-control actuation, where Hessian and wrinkling instabilities can occur once certain critical voltages are reached.
For the mechanical pre-stresses, two modes that can be implemented in practice are used: equi-biaxial and uni-axial. We confirm the analytical and numerical stability results of homogeneous deformation modes with Finite Element simulations of real actuations, where inhomogeneous fields may develop. We find complete agreement in the equi-biaxial case, and very close agreement in the uni-axial case, when the pre-stress is due to a dead-load weight. In the latter case, the simulations show that small inhomogeneous effects develop near the clamps, and eventually a compressive lateral stress emerges, leading to a breakdown of the numerics. - arXiv:2003.07246 [pdf, ps, other]
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Title: Theory of the highly viscous flowAuthors: U. BuchenauComments: theory complementedSubjects: Disordered Systems and Neural Networks (cond-mat.dis-nn); Soft Condensed Matter (cond-mat.soft)
In an undercooled liquid close to the glass transition, the flow begins by many thermally activated back-and-forth jumps, structural Eshelby rearrangements of strained regions. Together, they lead at short times t to the Kohlrausch t^beta shear relaxation, with beta around 1/2, before the jumps become irreversible and the viscous flow begins. The Kohlrausch behavior is not yet well understood. Here, a theoretical explanation is given, starting from an exact result for the irreversible jumps, the lifetime distribution of the critical Eshelby region. The barrier for the Eshelby transitions is decomposed into a sum over all vibrational modes which have to find a new minimum. A new close-packing picture is proposed for the numerically found string motion in soft vibrations and low-barrier relaxations in glasses. It enables a quantitative calculation of the Kohlrausch exponent for metallic glasses. A continuity relation between the irreversible and the reversible Kohlrausch relaxation time distribution is derived. The full spectrum can be used in many ways, not only to describe shear relaxation data, but also to relate shear relaxation data to dielectric and bulk relaxation spectra, and to predict aging from shear relaxation data, as demonstrated for a very recent aging experiment.
- arXiv:2003.07247 [pdf]
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Title: Manufacture and Characterization of Graphene Membranes with Suspended Silicon Proof Masses for MEMS and NEMS ApplicationsAuthors: Xuge Fan (1), Anderson D. Smith (3), Fredrik Forsberg (1), Stefan Wagner (2), Stephan Schröder (1), Sayedeh Shirin Afyouni Akbari (4), Andreas C. Fischer (1, 5) Luis Guillermo Villanueva (4), Mikael Östling (3), Max C. Lemme (2, 3), Frank Niklaus (1) ((1) Division of Micro and Nanosystems, KTH Royal Institute of Technology, (2) Faculty of Electrical Engineering and Information Technology, RWTH Aachen University, (3) Division of Integrated Devices and Circuits, KTH Royal Institute of Technology, (4) Advanced NEMS Group, École Polytechnique Fédérale de Lausanne (EPFL), (5) Silex Microsystems AB)Comments: 39 pages, 15 figuresSubjects: Applied Physics (physics.app-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Unparalleled strength, chemical stability, ultimate surface-to-volume ratio and excellent electronic properties of graphene make it an ideal candidate as a material for membranes in micro- and nanoelectromechanical systems (MEMS and NEMS). However, the integration of graphene into MEMS or NEMS devices and suspended structures such as proof masses on graphene membranes raises several technological challenges, including collapse and rupture of the graphene. We have developed a robust route for realizing membranes made of double-layer CVD graphene and suspending large silicon proof masses on membranes with high yields. We have demonstrated the manufacture of square graphene membranes with side lengths from 7 micro meter to 110 micro meter and suspended proof masses consisting of solid silicon cubes that are from 5 micro meter multiply 5 micro meter multiply 16.4 micro meter to 100 micro meter multiply 100 micro meter multiply 16.4 micro meter in size. Our approach is compatible with wafer-scale MEMS and semiconductor manufacturing technologies, and the manufacturing yields of the graphene membranes with suspended proof masses were greater than 90%, with more than 70% of the graphene membranes having more than 90% graphene area without visible defects. The graphene membranes with suspended proof masses were extremely robust and were able to withstand indentation forces from an atomic force microscope (AFM) tip of up to ~7000 nN. The measured resonance frequencies of the realized structures ranged from tens to hundreds of kHz, with quality factors ranging from 63 to 148. The proposed approach for the reliable and large-scale manufacture of graphene membranes with suspended proof masses will enable the development and study of innovative NEMS devices with new functionalities and improved performances.
- arXiv:2003.07261 [pdf, other]
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Title: Protected helical transport in magnetically doped quantum wires: beyond the 1D paradigmComments: Slightly polished version, improved bibliographySubjects: Strongly Correlated Electrons (cond-mat.str-el); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
One-dimensional (1D) quantum wires, which are functionalized by magnetic ad-atoms, can host ballistic helical transport. Helicity protects transport from an undesirable influence of material imperfections and makes the magnetically doped wire very promising elements for nanoelectronics and spintronics. However, fabricating purely 1D conductors is experimentally very challenging and not always feasible. In this paper, we show that the protected helical transport can exist even in quasi-1D wires. We model the quasi-1D magnetically doped wire as two coupled dense 1D Kondo chains. Each chain consists of itinerant electrons interacting with localized quantum magnetic moments - Kondo impurities. We have analyzed the regimes of weak-, intermediate- and strong inter-chain coupling and found conditions necessary for the origin of the aforementioned protected transport. Our results give a push for experimental realizations of the helical states in magnetically doped wires.
- arXiv:2003.07267 [pdf, other]
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Title: Recovery of damaged information and the out-of-time-ordered correlatorsComments: 5+1 pages, 3+3 figures; V2: Improved presentation, new model study addedSubjects: Quantum Physics (quant-ph); Statistical Mechanics (cond-mat.stat-mech); Chaotic Dynamics (nlin.CD)
A time-reversed dynamics unwinds information scrambling, which is induced during the time-forward evolution with a complex Hamiltonian. We show that if the scrambled information is, in addition, partially damaged by a local measurement, then such a damage can still be treated by application of the time-reversed protocol. This information recovery is described by the long-time saturation value of a certain out-of-time-ordered correlator of local variables. We also propose a simple test that distinguishes between quantum and reversible classical chaotic information scrambling.
- arXiv:2003.07271 [pdf, ps, other]
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Title: Spin-orbit torques originating from bulk and interface in Pt-based structuresSubjects: Materials Science (cond-mat.mtrl-sci); Applied Physics (physics.app-ph)
The origin of spin-orbit torques in prototypical Pt-based spintronic devices strongly depends on the choice of the ferromagnetic layer. We show that, in a Pt/Ni bilayer, the bulk spin Hall effect in the Pt layer is responsible for both damping-like and field-like torques. In contrast, the interfacial spin-orbit coupling dominates the damping-like torque in a Pt/Fe bilayer, where the Ni layer is replaced with Fe, despite the strong spin Hall effect in the Pt layer. The reason for this is that the strong spin-orbit coupling at the Pt/Fe interface generates the sizable damping-like torque, while it suppresses the damping-like torque arising from the bulk through the dissipation of the spin Hall current at the interface. Although the bulk spin Hall effect plays a minor role in the generation of the damping-like torque in the Pt/Fe bilayer, the bulk effect is significant in the generation of the field-like torque, which arises from a rotation of the spin direction of the spin Hall current at the Pt/Fe interface. We found that the direction of the field-like torque originating from the spin Hall effect is opposite between the Pt/Ni and Pt/Fe bilayers. This difference is attributed to the opposite sign of the imaginary part of the spin-mixing conductance due to different spin-dependent potentials at the Pt/Ni and Pt/Fe interfaces. These results show that the bulk spin-orbit torques, as well as the interfacial spin-orbit torques, can be controlled by the interface engineering.
- arXiv:2003.07280 [pdf, other]
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Title: Restricted Boltzmann machine representation for the groundstate and excited states of Kitaev Honeycomb modelComments: 18 pages, 9 figures, 4 tablesSubjects: Disordered Systems and Neural Networks (cond-mat.dis-nn); Strongly Correlated Electrons (cond-mat.str-el)
In this work, the capability of restricted Boltzmann machines (RBMs) to find solutions for the Kitaev honeycomb model is investigated. The measured groundstate (GS) energy of the system is compared and shown to reside within less than $5\%$ error of the analytically derived value of the energy. Moreover, given a set of single shot measurements of exact solutions of the model, an RBM is used to perform quantum state tomography and the obtained result has a $97\%$ overlap with the exact analytic result. Furthermore, the possibility of realizing anyons in the RBM is discussed and an algorithm is given to build these anyonic excitations and braid them as a proof of concept for performing quantum gates and doing quantum computation.
- arXiv:2003.07296 [pdf]
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Title: Faraday effect and fragmentation of ferromagnetic layers in multilayer Co/Cu(111) nanofilmsAuthors: Irene N. Lukienko, Mykola F. Kharchenko, Alexey V. Fedorchenko, Ivan A. Kharlan, Olga P. Tutakina, Olexandr N. Stetsenko, Cristina S. Neves, Andrei N. SalakComments: 10 pages, 9 figuresJournal-ref: J. Magn. Magn. Mat. 505 (2020) 166706Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
With purpose to investigate influence of magnetically non-active metal layers on the Faraday effect in multilayer Ferromagnetic/Normal metal films, dependences of the Faraday rotation angles of the light polarization plane on magnetic field have been studied in multilayer [Co/Cu] nanofilms. It was revealed that the Faraday rotation varies with thickness of the Cu layers. This dependence of the Faraday rotation on the Cu layer thickness consists of the monotonic component, namely a gradual rise of the angle with increase of the Cu layer thickness, and the non-monotonic one represented by two minima. The monotonic changes of the Faraday rotation were satisfactory described in frames of the effective medium method. Two minima are explained with the Co layers fragmentation due to influence of size electron quantization in the Cu layers on formation of Co clusters during deposition of the films.
- arXiv:2003.07303 [pdf, other]
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Title: Topological Hall signatures of magnetic hopfionsComments: 6 pages, 4 figuresJournal-ref: Physical Review Research 2, 013315 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Strongly Correlated Electrons (cond-mat.str-el)
Magnetic hopfions are topologically protected three-dimensional solitons that are constituted by a tube which exhibits a topologically nontrivial spin texture in the cross-section profile and is closed to a torus. Here we show that the hopfion's locally uncompensated emergent field leads to a topological Hall signature, although the topological Hall effect vanishes on the global level. The topological Hall signature is switchable by magnetic fields or electric currents and occurs independently of the anomalous and conventional Hall effects. It can therefore be exploited to electrically detect hopfions in experiments and even to distinguish them from other textures like skyrmion tubes. Furthermore, it can potentially be utilized in spintronic devices. Exemplarily, we propose a hopfion-based racetrack data storage device and simulate the electrical detection of the hopfions as carriers of information.
- arXiv:2003.07313 [pdf, ps, other]
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Title: Clustering in two models of interacting motorsSubjects: Statistical Mechanics (cond-mat.stat-mech); Soft Condensed Matter (cond-mat.soft)
We study a two-species bidirectional exclusion process, and a single species variant, which is motivated by the motion of organelles and vesicles along microtubules. Specifically, we are interested in the clustering of the particles and appearance of a single large cluster as the ratio $Q$ of the translation to switching rates is varied. We find that, although for a finite system, there is a clustering phenomenon in which the probability of finding a single large cluster changes from being negligible to having finite values, the phenomenon shifts to larger $Q$ values as the system size is increased. This suggests that the observed clustering is not a true (nonequilibrium) transition in the thermodynamic sense but rather a finite-size effect.
- arXiv:2003.07327 [pdf, other]
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Title: Modelling inelastic granular media using Dynamical Density Functional TheorySubjects: Statistical Mechanics (cond-mat.stat-mech)
We construct a new mesoscopic model for granular media using Dynamical Density Functional Theory (DDFT). The model includes both a collision operator to incorporate inelasticity and the Helmholtz free energy functional to account for external potentials, interparticle interactions and volume exclusion. We use statistical data from event-driven microscopic simulations to determine the parameters not given analytically by the closure relations used to derive the DDFT. We numerically demonstrate the crucial effects of each term in the DDFT, and the importance of including an accurately parametrised pair correlation function.
- arXiv:2003.07346 [pdf, other]
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Title: Structure and charge transport of amorphous $Cu$-doped $Ta_2O_5$ : An ab initio studyJournal-ref: Phys. Rev. Materials 4, 064603, (2020)Subjects: Materials Science (cond-mat.mtrl-sci); Disordered Systems and Neural Networks (cond-mat.dis-nn)
In this paper, we present ab initio computer models of Cu-doped amorphous Ta2O5 , a promising candidate for Conducting Bridge Random Access Memory (CBRAM) memory devices, and study the structural, electronic, charge transport and vibrational properties based on plane-wave density functional methods. We offer an atomistic picture of the process of phase segregation/separation between Cu and Ta2O5 subnetworks. Electronic calculations show that the models are conducting with extended Kohn-Sham orbitals around the Fermi level. In addition to that, we also characterize the electronic transport using the Kubo-Greenwood formula modified suitably to calculate the space-projected conductivity (SPC). Our SPC calculations show that Cu clusters and under-coordinated Ta adjoining the Cu are the conduction-active parts of the network. We also report information about the dependence of the electrical conductivity on the connectivity of the Cu sub-matrix. Vibrational calculations for one of the models has been undertaken with an emphasis on localization and animation of representative modes.
Replacements
- arXiv:1705.10235 (replaced) [pdf, other]
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Title: High pressure Raman study of the quantum magnet (C$_4$H$_{12}$N$_2$)Cu$_2$Cl$_6$Authors: Simon Bettler, Gediminas Simutis, Gérard Perren, Dominic Blosser, Severian Gvasaliya, Andrey ZheludevJournal-ref: Phys. Rev. B 96, 174431 (2017)Subjects: Strongly Correlated Electrons (cond-mat.str-el)
Magnetic and lattice excitations in the quantum antiferromagnet (C$_4$H$_{12}$N$_2$)Cu$_2$Cl$_6$ (PHCC) are studied across two pressure-induced phase transition at $P_c=4.3~\mathrm{kbar}$ and $P_1=13.4~\mathrm{kbar}$ using Raman spectroscopy. It is confirmed that neither transition is a result of a structural transformation. Magnetic scattering is detected. It shows a pronounced pressure dependence and undergoes substantial changes at both transitions. The results are in clear contradiction with previous neutron studies, which detected only minor changes of the magnon spectrum at $P_1$. A number of phonons show anomalous frequency shifts at low temperatures. This effect is pressure dependent and for two of the observed phonons dramatically reverses sign at around $P_1$. The anomalous behavior is attributed to strong magnetoelastic coupling in PHCC.
- arXiv:1712.08775 (replaced) [pdf, other]
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Title: Note on Green Function Formalism and Topological InvariantsComments: 19 pages, 3 figuresJournal-ref: J. Stat. Mech. (2020) 033101Subjects: High Energy Physics - Theory (hep-th); Strongly Correlated Electrons (cond-mat.str-el); Mathematical Physics (math-ph); Algebraic Topology (math.AT)
It has been discovered previously that the topological order parameter could be identified from the topological data of the Green's function, namely the (generalized) TKNN invariant in general dimensions, for both non-interacting and interacting systems. In this note, we show that this phenomenon has a clear geometric derivation. This proposal could be regarded as an alternative proof for the identification of the corresponding topological invariant and the topological order parameter.
- arXiv:1811.08349 (replaced) [pdf, ps, other]
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Title: Spinning Gyroscope in an Acoustic Black Hole : Precession Effects and Observational AspectsComments: 12 pages including 4 figures, accepted for publication in EPJCJournal-ref: Eur. Phys. J. C 80:493 (2020)Subjects: General Relativity and Quantum Cosmology (gr-qc); Other Condensed Matter (cond-mat.other); High Energy Physics - Theory (hep-th)
The exact precession frequency of a freely-precessing test gyroscope is derived for a $2+1$ dimensional rotating acoustic black hole analogue spacetime, without making the somewhat unrealistic assumption that the gyroscope is static. We show that, as a consequence, the gyroscope crosses the acoustic ergosphere of the black hole with a finite precession frequency, provided its angular velocity lies within a particular range determined by the stipulation that the Killing vector is timelike over the ergoregion. Specializing to the `Draining Sink' acoustic black hole, the precession frequency is shown to diverge near the acoustic horizon, instead of the vicinity of the ergosphere. In the limit of an infinitesimally small rotation of the acoustic black hole, the gyroscope still precesses with a finite frequency, thus confirming a behaviour analogous to geodetic precession in a physical non-rotating spacetime like a Schwarzschild black hole. Possible experimental approaches to detect acoustic spin precession and measure the consequent precession frequency, are discussed.
- arXiv:1902.02301 (replaced) [pdf, ps, other]
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Title: Relativistic Impulse Approximation in Compton ScatteringAuthors: Chen-Kai Qiao, Hsin-Chang Chi, Lei Zhang, Peng Gu, Cheng-Pang Liu, Chang-Jian Tang, Shin-Ted Lin, Keh-Ning HuangComments: 20 pages, 13 figures, 1 table and 5 Appendices. Originally created in Feb 2019, V2 and V3: minor revision; V4: major revision, add 2 Appendices; V5: accepted manuscript; V6: published versionJournal-ref: Journal of Physics B: Atomic, Molecular and Optical Physics, 53(07), 075002 (2020)Subjects: Atomic Physics (physics.atom-ph); Other Condensed Matter (cond-mat.other)
Relativistic impulse approximation (RIA) has been widely used in atomic, condensed matter, nuclear, and elementary particle physics. In former treatments of RIA formulation, differential cross sections for Compton scattering processes were factorized into atomic Compton profiles by performing further simplified approximations in the integration. In this study, we develop an ``exact'' numerical method without using any further simplified approximations or factorization treatments. The validity of the approximations and factorizations used in former RIA treatments can be tested using our approach. Calculations for C, Cu, Ge, and Xe atomic systems are carried out using Dirac-Fock wavefunctions, and comparisons between the proposed approach and former treatments of RIA are performed and discussed in detail. Numerical results indicate that these simplified approximations work reasonably in the Compton peak region, and our results have little difference with the best of the former RIA treatments in the entire energy region. While in regions far from the Compton peak, the RIA results become inaccurate, even when our ``exact'' numerical treatment is used.
- arXiv:1902.08376 (replaced) [pdf]
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Title: Crystallisation From Volatile Deep Eutectic SolventsComments: 42 pages, 23 figures, 1 TableSubjects: Chemical Physics (physics.chem-ph); Materials Science (cond-mat.mtrl-sci)
A new class of deep eutectic solvents are presented where one component of the system is inherently volatile, enabling a premeditated, auto-destructive capability which leads inexorably to a series of novel crystal structures. These volatile deep eutectic solvents are easily-formed liquids with a greatly depressed melting point and exhibit all of the physical characteristics of classical deep eutectic solvents, with the exception that the hydrogen-bond donor component is volatile when exposed to the atmosphere at room temperature. We demonstrate the effectiveness of this concept through the exquisite control of pharmaceutical polymorphism, among which is a more efficacious form of acetaminophen, which can be formed spontaneously for the first time at room temperature.
- arXiv:1903.05336 (replaced) [pdf, other]
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Title: Topology by Dissipation: Transport propertiesComments: Published version. 14 pages, 12 figuresJournal-ref: Phys. Rev. B 101, 125412 (2020)Subjects: Quantum Gases (cond-mat.quant-gas); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Strongly Correlated Electrons (cond-mat.str-el)
Topological phases of matter are the center of much current interest, with promising potential applications in, e.g., topologically-protected transport and quantum computing. Traditionally such states are prepared by tuning the system Hamiltonian while coupling it to a generic bath at very low temperatures; This approach is often ineffective, especially in cold-atom systems. It was recently shown that topological phases can emerge much more efficiently even in the absence of a Hamiltonian, by properly engineering the interaction of the system with its environment, to directly drive the system into the desired state. Here we concentrate on dissipatively-induced 2D Chern insulator (lattice quantum Hall) states. We employ open quantum systems tools to explore their transport properties, such as persistent currents and the conductance in the steady state, in the presence of various Hamiltonians. We find that, in contrast with equilibrium systems, the usual relation between the Chern topological number and the Hall conductance is broken. We explore the intriguing edge behaviors and elucidate under which conditions the Hall conductance is quantized.
- arXiv:1905.07611 (replaced) [pdf, ps, other]
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Title: Large fluctuations in non-ideal coarse-grained systemsComments: 5 pages 3 figuresSubjects: Computational Physics (physics.comp-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Using the recently introduced Molecular Dynamics Lattice Gas (MDLG) approach, we test fluctuations of coarse-grained quantities. We show that as soon as the system can no longer be considered an ideal gas fluctuations fail to diminish upon coarse-graining as is usually expected. These results suggest that current approaches to simulating fluctuating hydrodynamics may have to be augmented to achieve quantitative results for systems with a non-ideal equation of state. The MDLG method gives a guidance to the exact nature of the fluctuation in such systems.
- arXiv:1905.08808 (replaced) [pdf, other]
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Title: Dissipation assisted Thouless pumping in the Rice-Mele modelComments: 21 pages, 8 figuresJournal-ref: J. Stat. Mech. (2020) 043101Subjects: Quantum Gases (cond-mat.quant-gas); Quantum Physics (quant-ph)
We investigate the effect of dissipation from a thermal environment on topological pumping in the periodically-driven Rice-Mele model. We report that dissipation can improve the robustness of pumping quantisation in a regime of finite driving frequencies. Specifically, in this regime, a low-temperature dissipative dynamics can lead to a pumped charge that is much closer to the Thouless quantised value, compared to a coherent evolution. We understand this effect in the Floquet framework: dissipation increases the population of a Floquet band which shows a topological winding, where pumping is essentially quantised. This finding is a step towards understanding a potentially very useful resource to exploit in experiments, where dissipation effects are unavoidable. We consider small couplings with the environment and we use a Bloch-Redfield quantum master equation approach for our numerics: Comparing these results with an exact MPS numerical treatment we find that the quantum master equation works very well also at low temperature, a quite remarkable fact.
- arXiv:1906.02709 (replaced) [pdf, other]
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Title: Higher-Order Topological Superconductivity of Spin-Polarized FermionsComments: 6+13 pages, 2+1 figures; accepted versionJournal-ref: Phys. Rev. Research 2, 012060 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Superconductivity (cond-mat.supr-con)
We study the superconductivity of spin-polarized electrons in centrosymmetric ferromagnetic metals. Due to the spin-polarization and the Fermi statistics of electrons, the superconducting pairing function naturally has odd parity. According to the parity formula proposed by Fu, Berg, and Sato, odd-parity pairing leads to conventional first-order topological superconductivity when a normal metal has an odd number of Fermi surfaces. Here, we derive generalized parity formulae for the topological invariants characterizing higher-order topology of centrosymmetric superconductors. Based on the formulae, we systematically classify all possible band structures of ferromagnetic metals that can induce inversion-protected higher-order topological superconductivity. Among them, doped ferromagnetic nodal semimetals are identified as the most promising normal state platform for higher-order topological superconductivity. In two dimensions, we show that odd-parity pairing of doped Dirac semimetals induces a second-order topological superconductor. In three dimensions, odd-parity pairing of doped nodal line semimetals generates a nodal line topological superconductor with monopole charges. On the other hand, odd-parity pairing of doped monopole nodal line semimetals induces a three-dimensional third-order topological superconductor. Our theory shows that the combination of superconductivity and ferromagnetic nodal semimetals opens up a new avenue for future topological quantum computations using Majorana zero modes.
- arXiv:1906.09663 (replaced) [pdf, other]
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Title: Rejuvenation and Shear-Banding in model amorphous solidsJournal-ref: Phys. Rev. E 101, 033001 (2020)Subjects: Materials Science (cond-mat.mtrl-sci)
We measure the local yield stress, at the scale of small atomic regions, in a deeply quenched two-dimensional glass model undergoing shear banding in response to athermal quasistatic (AQS) deformation. We find that the occurrence of essentially a single plastic event suffices to bring the local yield stress distribution to a well-defined value for all strain orientations, thus essentially erasing the memory of the initial structure. It follows that in a well-relaxed sample, plastic events cause the abrupt (nucleation-like) emergence of a local softness contrast and thus precipitate the formation of a band, which, in its early stages, is measurably softer than the steady-state flow. Moreover, this postevent yield stress ensemble presents a mean value comparable to that of the inherent states of a supercooled liquid around the mode-coupling temperature $T_{\rm MCT}$. This, we argue, explains that the transition between brittle and ductile yielding in amorphous materials occurs around a comparable parent temperature. Our data also permit to capture quantitatively the contributions of pressure and density changes and demonstrate unambiguously that they are negligible compared with the changes of softness caused by structural rejuvenation.
- arXiv:1907.00383 (replaced) [pdf, other]
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Title: Split-ring polariton condensates as macroscopic two-level quantum systemsComments: 9 pages, 7 figures, supplementary materialsSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Quantum Physics (quant-ph)
Superposition states of circular currents of exciton-polaritons mimic the superconducting flux qubits. The phase of a polariton fluid must change by an integer number of $2\pi$, when going around the ring. If one introduces a $\pi$-phase delay line in the ring, the fluid is obliged to propagate a clockwise or anticlockwise circular current to reduce the total phase gained over one round-trip to zero or to build it up to $2\pi$. We show that such a $\pi$-delay line can be provided by a dark soliton pinned to a potential well created by a C-shape non-resonant pump-spot. The resulting split-ring polariton condensates exhibit pronounced coherent oscillations passing periodically through clockwise and anticlockwise current states. These oscillations may persist far beyond the coherence time of polariton condensates. The qubits based on split-ring polariton condensates are expected to possess very high figures of merit that makes them a valuable alternative to superconducting qubits. We propose a design of the $i$SWAP gate based on a pair of coupled polariton qubits.
- arXiv:1907.01855 (replaced) [pdf, other]
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Title: Thermodynamics from first principles: correlations and nonextensivityComments: 6 pages, 1 figure, 1 table, and 3 pages of supplemental material. v4: comments are welcomeJournal-ref: Phys. Rev. E 101, 060101(R) (2020)Subjects: Statistical Mechanics (cond-mat.stat-mech); Classical Physics (physics.class-ph)
The standard formulation of thermostatistics, being based on the Boltzmann-Gibbs distribution and logarithmic Shannon entropy, describes idealized uncorrelated systems with extensive energies and short-range interactions. In this letter, we use the fundamental principles of ergodicity (via Liouville's theorem), the self-similarity of correlations, and the existence of the thermodynamic limit to derive generalized forms of the equilibrium distribution for long-range-interacting systems. Significantly, our formalism provides a justification for the well-studied nonextensive thermostatistics characterized by the Tsallis distribution, which it includes as a special case. We also give the complementary maximum entropy derivation of the same distributions by constrained maximization of the Boltzmann-Gibbs-Shannon entropy. The consistency between the ergodic and maximum entropy approaches clarifies the use of the latter in the study of correlations and nonextensive thermodynamics.
- arXiv:1907.04107 (replaced) [pdf, other]
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Title: Rabi oscillations in a superconducting nanowire circuitAuthors: Yannick Schön, Jan Nicolas Voss, Micha Wildermuth, Andre Schneider, Sebastian T. Skacel, Martin P. Weides, Jared H. Cole, Hannes Rotzinger, Alexey V. UstinovSubjects: Superconductivity (cond-mat.supr-con); Disordered Systems and Neural Networks (cond-mat.dis-nn); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Quantum Physics (quant-ph)
We investigate the circuit quantum electrodynamics of anharmonic superconducting nanowire oscillators. The sample circuit consists of a capacitively shunted nanowire with a width of about 20 nm and a varying length up to 350 nm, capacitively coupled to an on-chip resonator. By applying microwave pulses we observe Rabi oscillations, measure coherence times and the anharmonicity of the circuit. Despite the very compact design, simple top-down fabrication and high degree of disorder in the oxidized (granular) aluminum material used, we observe lifetimes in the microsecond range.
- arXiv:1907.08241 (replaced) [pdf, other]
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Title: Spontaneous symmetry breaking and Nambu-Goldstone modes in open classical and quantum systemsComments: 29 pages, 3 figures; typos corrected, published versionJournal-ref: Prog Theor Exp Phys (2020)Subjects: High Energy Physics - Theory (hep-th); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Quantum Gases (cond-mat.quant-gas); High Energy Physics - Phenomenology (hep-ph)
We discuss spontaneous symmetry breaking of open classical and quantum systems. When a continuous symmetry is spontaneously broken in an open system, a gapless excitation mode appears corresponding to the Nambu-Goldstone mode. Unlike isolated systems, the gapless mode is not always a propagation mode, but it is a diffusion one. Using the Ward-Takahashi identity and the effective action formalism, we establish the Nambu-Goldstone theorem in open systems, and derive the low-energy coefficients that determine the dispersion relation of Nambu-Goldstone modes. Using these coefficients, we classify the Nambu-Goldstone modes into four types: type-A propagation, type-A diffusion, type-B propagation, and type-B diffusion modes.
- arXiv:1907.11116 (replaced) [pdf, other]
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Title: Magnetic memory effect in ensembles of interacting anisotropic magnetic nanoparticlesComments: 13 pages, 10 figuresSubjects: Materials Science (cond-mat.mtrl-sci)
We explore the influence of demagnetization interaction on magnetic memory effect by varying organization geometry of anisotropic ZnFe$_2$O$_4$ nanoparticles in an ensemble. The static and dynamic behaviour of two differently organized ensembles, compact ensemble (CE) and hollow core ensemble (HCE), are extensively studied by both dc and ac susceptibility, magnetic memory effect and spin relaxation. The frequency-dependence peak shifting of freezing temperature in both the systems is analyzed properly with the help of two dynamic scaling models: Vogel-Fulcher law and power law. Presence of cluster spin-glass phase is reflected from Vogel-Fulcher temperature $T_0$ $\simeq$ 142.58 K for CE, $\simeq$ 97 K for HCE and characteristic time constant $\tau_0$ $\simeq$ $8.85\times10^{-9}$ s for CE, $\simeq$ $3.8\times10^{-10}$ s for HCE; along with $\delta$T$_{Th}$ $\sim$ 0.1 for CE and 0.2 for HCE. The power law fitting with dynamic exponent $zv'$ = 6.2 $\pm$ 1.1 for CE, 6.3 $\pm$ 0.5 for HCE and single spin flip $\tau^*$ $\simeq$ $7.7\times10^{-11}$ s for CE, $\simeq$ $1.3\times10^{-10}$ s for HCE provide firm confirmation of cluster spin-glass phase. The progressive spin freezing across multiple metastable states with prominent memory effects is reflected in both the systems via nonequilibrium dynamics study. The hollow core geometry with anisotropic nanoparticles on surface with closer proximity leads to complex anisotropy energy landscape with enhanced demagnetizing field resulting highly frustrated surface spins. As a consequence, more prominent magnetic memory effect is observed in HCE with higher activation energy, reduced blocking temperature and enhanced coercivity than that of CE.
- arXiv:1908.02066 (replaced) [pdf, other]
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Title: Non-Hermitian Floquet topological phases in the double-kicked rotorComments: 13 pages, 9 figuresJournal-ref: Phys. Rev. A 100, 053608 (2019)Subjects: Quantum Physics (quant-ph); Other Condensed Matter (cond-mat.other); Quantum Gases (cond-mat.quant-gas)
Dynamical kicking systems possess rich topological structures. In this work, we study Floquet states of matter in a non-Hermitian extension of double kicked rotor model. Under the on-resonance condition, we find various non-Hermitian Floquet topological phases, with each being characterized by a pair of topological winding numbers. A generalized mean chiral displacement is introduced to detect these winding numbers dynamically in two symmetric time frames. Furthermore, by mapping the system to a periodically quenched lattice model, we obtain the topological edge states and unravel the bulk-edge correspondence of the non-Hermitian double kicked rotor. These results uncover the richness of Floquet topological states in non-Hermitian dynamical kicking systems.
- arXiv:1908.03388 (replaced) [pdf, other]
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Title: Sustained coherent spin wave emission using frequency combsComments: 7 pages, 7 figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Applied Physics (physics.app-ph)
We demonstrate sustained coherent emission of spin waves in NiFe films using rapid demagnetization from high repetition rate femtosecond laser pulse trains. As the pulse separation is shorter than the magnon decay time, magnons having a frequency equal to a multiple of the 1 GHz repetition-rate are coherently amplified. Using scanning micro-Brillouin Light Scattering (BLS) we observe this coherent amplification as strong peaks spaced 1 GHz apart. The BLS counts vs. laser power exhibit a stronger than parabolic dependence consistent with counts being proportional to the square of the magnetodynamic amplitude, and the demagnetization pulse strength being described by a Bloch law. Spatial spin wave mapping demonstrates how both localized and propagating spin waves can be excited, and how the propagation direction can be directly controlled. Our results demonstrate the versatility of BLS spectroscopy for rapid demagnetization studies and enable a new platform for photo-magnonics where sustained coherent spin waves can be utilized.
- arXiv:1909.00545 (replaced) [pdf, other]
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Title: Two floating camphor particles interacting through lateral capillary forceAuthors: Yuhei Hirose, Yusuke Yasugahira, Mamoru Okamoto, Yuki Koyano, Hiroyuki Kitahata, Masaharu Nagayama, Yutaka SuminoComments: 9 pages, 6 figuresSubjects: Pattern Formation and Solitons (nlin.PS); Soft Condensed Matter (cond-mat.soft)
We consider a mathematical model for a two-particle system driven by the spatial gradient of a concentration field of chemicals with conservative attractive interactions in one dimension. This setup corresponds to an experimental system with floating camphor particles at a water surface. Repulsive interaction is introduced, as well as self-propelling force, through the concentration field of camphor molecules at the water surface. Here we newly adopt the attractive lateral capillary force due to the deformation of the water surface. The particles experience competing dissipative repulsion and conservative attraction. We numerically investigated the mathematical model, and found six different modes of motion. The theoretical approach revealed that some of such mode transitions can be understood in terms of bifurcation.
- arXiv:1909.02482 (replaced) [pdf, other]
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Title: Nanoscale phase separation and pseudogap in the hole-doped cuprates from fluctuating Cu-O-Cu bondsAuthors: Sergi Julià-Farré, Alexandre Dauphin, Ravindra W. Chhajlany, Piotr T. Grochowski, Simon Wall, Maciej Lewenstein, Przemysław R. GrzybowskiComments: 10 pages, 8 figures, 1 table. Revised version published in Physical Review BJournal-ref: Phys. Rev. B 101, 125107 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el)
The pseudogap phenomenology is one of the enigmas of the physics of high-Tc superconductors. Many members of the cuprate family have now been characterized with high resolution in both real and momentum space, which revealed highly anisotropic Fermi arcs and local domain which break rotational symmetry in the CuO2 plane at the intraunit cell level. While most theoretical approaches to date have focused on the role of electronic correlations and doping-induced disorder to explain these features, we show that many features of the pseudogap phase can be reproduced by considering the interplay between electronic and nonlinear electron-phonon interactions within a model of fluctuating Cu-O-Cu bonds. Remarkably, we find electronic segregation arises naturally without the need to explicitly include disorder. Our approach points not only to the key role played by the oxygen bond in the pseudogap phase, but opens different directions to explore how nonequilibrium lattice excitation can be used to control the properties of the pseudogap phase.
- arXiv:1909.04590 (replaced) [pdf, other]
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Title: Nonlinear thermoelectricity with electron-hole symmetric systemsComments: biblio information updatedJournal-ref: Phys. Rev. Lett. 124, 106801 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Statistical Mechanics (cond-mat.stat-mech); Superconductivity (cond-mat.supr-con)
In the linear regime, thermo-electric effects between two conductors are possible only in the presence of an explicit breaking of the electron-hole symmetry. We consider a tunnel junction between two electrodes and show that this condition is no longer required outside the linear regime. In particular, we demonstrate that a thermally-biased junction can display an absolute negative conductance (ANC), and hence thermo-electric power, at a small but finite voltage bias, provided that the density of states of one of the electrodes is gapped and the other is monotonically decreasing. We consider a prototype system that fulfills these requirements, namely a tunnel junction between two different superconductors where the Josephson contribution is suppressed. We discuss this nonlinear thermo-electric effect based on the spontaneous breaking of electron-hole symmetry in the system, characterize its main figures of merit and discuss some possible applications.
- arXiv:1909.10797 (replaced) [pdf, other]
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Title: Dynamical characterization of non-Hermitian Floquet topological phases in one-dimensionAuthors: Longwen ZhouComments: 9 pages, 4 figuresJournal-ref: Phys. Rev. B 100, 184314 (2019)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Quantum Physics (quant-ph)
Non-Hermitian topological phases in static and periodically driven systems have attracted great attention in recent years. Finding dynamical probes for these exotic phases would be of great importance in the detection and application of their topological properties. In this work, we propose a systematic approach to dynamically characterize non-Hermitian Floquet topological phases in one-dimension with chiral symmetry. We show that the topological invariants of a chiral symmetric Floquet system can be fully determined by measuring the winding angles of its time-averaged spin textures. We further purpose a piecewise quenched lattice model with rich non-Hermitian Floquet topological phases, in which our theoretical predictions are numerically demonstrated and compared with another approach utilizing the mean chiral displacement of a wavepacket.
- arXiv:1909.13855 (replaced) [pdf, other]
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Title: Topological skyrmion phases of matterAuthors: Ashley M. CookComments: 10 pages, 4 figures, updated introduction, expanded discussion on topological invariant and tight-binding model in main text, expanded discussion of type-II topological phase transition, added discussion on relevance to the ten-fold way, further discussion of experimental signaturesSubjects: Superconductivity (cond-mat.supr-con); Other Condensed Matter (cond-mat.other); Strongly Correlated Electrons (cond-mat.str-el)
We introduce topological phases of matter defined by non-trivial homotopy groups into the literature, the chiral and helical topological skyrmion phases of matter, which generalize and extend the concepts of the Chern insulator and quantum spin Hall insulator, respectively. Chiral and helical topological skyrmion phases of matter also possessing particle-hole symmetry may be realized in centrosymmetric superconductors. In this work, we consider tight-binding models for spin-triplet superconductivity in transition metal oxide compounds and find that such models can realize each of these topological skyrmion phases of matter. The chiral topological skyrmion superconductor phase is furthermore realized for a model and parameter set characterizing Sr$_2$RuO$_4$ with spin-triplet superconductivity. As well, one kind of topological phase transition by which the skyrmion number can change occurs without the closing of energy gaps in a system described by a quadratic Hamiltonian, without breaking the protecting symmetries, which contradicts the "flat band" limit assumption used in the development, for instance, of the entanglement spectrum, Wilson loops, and the ten-fold way classification scheme.
- arXiv:1910.01174 (replaced) [pdf, other]
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Title: Spatial Strength Centrality and the Effect of Spatial Embeddings on Network ArchitectureSubjects: Physics and Society (physics.soc-ph); Statistical Mechanics (cond-mat.stat-mech); Social and Information Networks (cs.SI); Combinatorics (math.CO); Adaptation and Self-Organizing Systems (nlin.AO)
For many networks, it is useful to think of their nodes as being embedded in a latent space, and such embeddings can affect the probabilities for nodes to be adjacent to each other. In this paper, we extend existing models of synthetic networks to spatial network models by first embedding nodes in Euclidean space and then modifying the models so that progressively longer edges occur with progressively smaller probabilities. We start by extending a geographical fitness model by employing Gaussian-distributed fitnesses, and we then develop spatial versions of preferential attachment and configuration models. We define a notion of "spatial strength centrality" to help characterize how strongly a spatial embedding affects network structure, and we examine spatial strength centrality on a variety of real and synthetic networks.
- arXiv:1910.03513 (replaced) [pdf, ps, other]
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Title: Hydrodynamic Bulge Testing: Materials Characterization without Measuring DeformationComments: 14 pages, 8 figures and 4 pages supplementary material with 1 figure; v2: minor corrections, fixing typos; v3: minor fixesJournal-ref: ASME Journal of Applied Mechanics 87, 051012 (2020)Subjects: Soft Condensed Matter (cond-mat.soft)
Characterizing the elastic properties of soft materials through bulge testing relies on accurate measurement of deformation, which is experimentally challenging. To avoid measuring deformation, we propose a hydrodynamic bulge test for characterizing the material properties of thick, pre-stressed elastic sheets via their fluid--structure interaction with a steady viscous fluid flow. Specifically, the hydrodynamic bulge test relies on a pressure drop measurement across a rectangular microchannel with a deformable top wall. We develop a mathematical model using first-order shear-deformation theory of plates with stretching, and the lubrication approximation for Newtonian fluid flow. Specifically, a relationship is derived between the imposed flow rate and the total pressure drop. Then, this relationship is inverted numerically to yield estimates of the Young's modulus (given the Poisson ratio), if the pressure drop is measured (given the steady flow rate). Direct numerical simulations of two-way-coupled fluid--structure interaction are carried out in ANSYS to determine the cross-sectional membrane deformation and the hydrodynamic pressure distribution. Taking the simulations as ``ground truth,'' a hydrodynamic bulge test is performed using the simulation data to ascertain the accuracy and validity of the proposed methodology for estimating material properties. An error propagation analysis is performed via Monte Carlo simulation to characterize the susceptibility of the hydrodynamic bulge test estimates to noise. We find that, while a hydrodynamic bulge test is less accurate in characterizing material properties, it is less susceptible to noise, in the input (measured) variable, than a hydrostatic bulge test.
- arXiv:1910.09766 (replaced) [pdf, other]
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Title: Probing Band-center Anomaly with the Kernel Polynomial MethodComments: 8 pages, 2 figuresSubjects: Disordered Systems and Neural Networks (cond-mat.dis-nn)
We investigate the anomalous behavior of localization length of a non-interacting one-dimensional Anderson model at zero temperature. We report numerical calculations of the Thouless expression of localization length, based on the Kernel polynomial method (KPM), which has an O(N ) computational complexity, where N is the system size. The KPM results show an excellent agreement with perturbative result in large system size limit, confirming the validity of Thouless formula. Thus, contrary to the previous numerical results, the KPM approximation of the Thouless expression produce the correct localization length at the band center. The Thouless expression relates localization length in terms of density of states in a one-dimensional disordered system. By calculating the KPM estimates of density of states, we find a cusp-like behavior around the band center in the perturbative regime. This cusp-like singularity can not be obtained by an approximate analytical calculations with in the second-order approximations, reflects the band-center anomaly.
- arXiv:1910.10728 (replaced) [pdf, other]
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Title: Orthogonality Catastrophe as a Consequence of the Quantum Speed LimitComments: 4.5+1 pages. 3+1 figures. Close to published versionJournal-ref: Phys. Rev. Lett. 124, 110601 (2020)Subjects: Quantum Physics (quant-ph); Quantum Gases (cond-mat.quant-gas); Statistical Mechanics (cond-mat.stat-mech)
A remarkable feature of quantum many-body systems is the orthogonality catastrophe which describes their extensively growing sensitivity to local perturbations and plays an important role in condensed matter physics. Here we show that the dynamics of the orthogonality catastrophe can be fully characterized by the quantum speed limit and, more specifically, that any quenched quantum many-body system whose variance in ground state energy scales with the system size exhibits the orthogonality catastrophe. Our rigorous findings are demonstrated by two paradigmatic classes of many-body systems -- the trapped Fermi gas and the long-range interacting Lipkin-Meshkov-Glick spin model.
- arXiv:1910.11000 (replaced) [pdf, other]
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Title: Fluctuations of work in realistic equilibrium states of quantum systems with conserved quantitiesComments: 12 pages, 1 fig. Contribution to Proceedings of the 24th European Conference on Few-Body Problems in Physics (EFB24). Matches journal version published under CC BY 4.0Journal-ref: SciPost Phys. Proc. 3, 024 (2020)Subjects: Quantum Physics (quant-ph); Statistical Mechanics (cond-mat.stat-mech); Atomic Physics (physics.atom-ph)
The out-of-equilibrium dynamics of quantum systems is one of the most fascinating problems in physics, with outstanding open questions on issues such as relaxation to equilibrium. An area of particular interest concerns few-body systems, where quantum and thermal fluctuations are expected to be especially relevant. In this contribution, we present numerical results demonstrating the impact of conserved quantities (or 'charges') in the outcomes of out-of-equilibrium measurements starting from realistic equilibrium states on a few-body system implementing the Dicke model.
- arXiv:1911.00174 (replaced) [pdf, other]
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Title: Nieh-Yan Anomaly: Torsional Landau Levels, central charge and anomalous thermal Hall effectComments: 6 pages, 3 figures. Published versionJournal-ref: Phys. Rev. B 101, 125201 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
The Nieh-Yan anomaly is the anomalous breakdown of the chiral U(1) symmetry caused by the interaction between torsion and fermions. We study this anomaly from the point of view of torsional Landau levels. It was found that the torsional Landau levels are gapless, while their contributions to the chiral anomaly are canceled, except those from the lowest torsional Landau levels. Hence, the dimension is effectively reduced from (3+1)-dimensional to (1+1)-dimensional. We further show that the coefficient of the Nieh-Yan anomaly is the free energy density in (1+1) dimensions. Especially, at finite temperature, the thermal Nieh-Yan anomaly is proportional to the central charge. The anomalous thermal Hall conductance in Weyl semimetals is then shown to be proportional to the central charge, which is the experimental fingerprint of the thermal Nieh-Yan anomaly.
- arXiv:1911.00739 (replaced) [pdf, other]
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Title: Model for growth and morphology of fungal myceliumComments: 12 pages, 10 figuresSubjects: Statistical Mechanics (cond-mat.stat-mech); Biological Physics (physics.bio-ph); Cell Behavior (q-bio.CB)
We present a minimal driven lattice gas model which generates the morphological characteristics associated with single colony mycelium arising from the growth and branching process of fungal hyphae, which is fed by a single source of nutrients. We first analyze the growth and transport process in the primary hypha modeled as a growing 1-d lattice, which is subject to particle (vesicle) loss due to presence of dynamically created branching sites. We show that the spatial profile of vesicles along the growing lattice is an exponential distribution, while the length grows logarithmically with time. We also find that the probability distribution of length of the hypha tends to a Gaussian distribution function at late times. In contrast, the probability distribution function of the time required for growth to a specific length tends to a broad log-normal distribution. We simulate the resultant 2-d morphology generated by the growing primary hypha, quantifying the motility behavior and morphological characteristics of the colony. Analysis of the temporal behavior and morphological characteristics of the resultant 2-d morphology reveals a wide variability of these characteristics which depend on the input parameters which characterize the branching and elongation dynamics of the hyphae. By calibrating the input parameters for our model, we make some quantitative comparison of the predictions of our model with the observed experimental growth characteristics of fungal hyphae and the morphological characteristics of single colony fungal mycelium.
- arXiv:1911.00931 (replaced) [pdf, other]
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Title: Dimension-free path-integral molecular dynamics without preconditioningComments: 13 pages, 6 figures. New results (for the 2 fs time-step) are added in Figure 1(d), y-axes of figure 6 are rescaled and a few typos are correctedJournal-ref: J. Chem. Phys. 152, 104102 (2020)Subjects: Chemical Physics (physics.chem-ph); Statistical Mechanics (cond-mat.stat-mech); Computational Engineering, Finance, and Science (cs.CE); Probability (math.PR)
Convergence with respect to imaginary-time discretization is an essential part of any path-integral-based calculation. However, an unfortunate property of existing non-preconditioned numerical integration schemes for path-integral molecular dynamics (PIMD) - including ring-polymer molecular dynamics (RPMD) and thermostatted RPMD (T-RPMD) - is that for a given MD timestep, the overlap between the exact ring-polymer Boltzmann-Gibbs distribution and that sampled using MD becomes zero in the infinite-bead limit. This has clear implications for hybrid Metropolis Monte-Carlo/MD sampling schemes. We show that these problems can be avoided through the introduction of "dimension-free" numerical integration schemes for which the sampled ring-polymer position distribution has non-zero overlap with the exact distribution in the infinite-bead limit for the case of a harmonic potential. We show that dimension freedom can be achieved via mollification of the forces from the physical potential and with the BCOCB integration scheme. The dimension-free numerical integration schemes yield finite error bounds for a given MD timestep as the number of beads is taken to infinity; these conclusions are proven for harmonic potential and borne out numerically for anharmonic systems, including water. The numerical results for BCOCB are particularly striking, allowing for three-fold increases in the stable timestep for liquid water with respect to the Bussi-Parrinello (OBABO) and Leimkuhler (BAOAB) integrators while introducing negligible errors in the statistical properties and absorption spectrum. Importantly, the dimension-free, non-preconditioned integration schemes introduced here preserve ergodicity and global second-order accuracy, and they remain simple, black-box methods that avoid additional computational costs, tunable parameters, or system-specific implementations.
- arXiv:1911.02456 (replaced) [pdf, other]
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Title: Anomalous Behavior of Magnetic Susceptibility Obtained by Quench Experiments in Isolated Quantum SystemsComments: 7 pages, 2 figures and Supplemental MaterialJournal-ref: Phys. Rev. Lett. 124, 110609 (2020)Subjects: Statistical Mechanics (cond-mat.stat-mech); Quantum Physics (quant-ph)
We examine how the magnetic susceptibility obtained by the quench experiment on isolated quantum systems is related to the isothermal and adiabatic susceptibilities defined in thermodynamics. Under the conditions similar to the eigenstate thermalization hypothesis, together with some additional natural ones, we prove that for translationally invariant systems the quench susceptibility as a function of wave vector k is discontinuous at k=0. Moreover, its values at k=0 and the k to 0 limit coincide with the adiabatic and the isothermal susceptibilities, respectively. We give numerical predictions on how these particular behaviors can be observed in experiments on the XYZ spin chain with tunable parameters, and how they deviate when the conditions are not fully satisfied.
- arXiv:1911.05006 (replaced) [pdf, other]
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Title: Driven Imposters: Controlling Expectations in Many-Body SystemsComments: 5 pages, 3 figures, will be accompanied by an extended submissionJournal-ref: Phys. Rev. Lett. 124, 183201 (2020)Subjects: Quantum Physics (quant-ph); Strongly Correlated Electrons (cond-mat.str-el)
We present a framework to control and track the observables of a general solid state system driven by an incident laser field. The main result is a non-linear equation of motion for tracking an observable, together with a constraint on the size of expectations which may be reproduced via tracking. Among other applications, this model provides a potential route to the design of laser fields which cause photo-induced superconductivity in materials above their critical temperature. As a first test, the strategy is used to make the expectation value of the current conform to an arbitrary function under a range of model parameters. Additionally, using two reference spectra for materials in the conducting and insulating regimes respectively, the tracking algorithm is used to make each material mimic the optical spectrum of the other.
- arXiv:1911.09907 (replaced) [pdf, other]
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Title: Boundary conformal spectrum and surface critical behaviors of the classical spin systems: a tensor network renormalization studyComments: 12 pages, 12 figuresJournal-ref: Phys. Rev. B 101, 155418 (2020)Subjects: Statistical Mechanics (cond-mat.stat-mech); Strongly Correlated Electrons (cond-mat.str-el); High Energy Physics - Lattice (hep-lat); High Energy Physics - Theory (hep-th)
We numerically obtain the conformal spectrum of several classical spin models on a two-dimensional lattice with open boundaries, for every boundary fixed point obtained by the Cardy's derivation [J. L. Cardy, Nucl. Phys. B 324, 581 (1989)]. In order to extract accurate conformal data, we implement the tensor network renormalization algorithm [G. Evenbly and G. Vidal, Phys. Rev. Lett. 115, 180405 (2015)] extended so as to be applicable to a square lattice with open boundaries. We successfully compute the boundary conformal spectrum consistent with the underlying boundary conformal field theories (BCFTs) for the Ising, tri-critical Ising, and 3-state Potts models on the lattice, which allows us to confirm the validity of the BCFT analyses for the surface critical behaviors of those lattice models.
- arXiv:1911.10899 (replaced) [pdf, ps, other]
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Title: Lifting of Coulomb Blockade by Alternating Voltages in Small Josephson Junctions with Electromagnetic Environment-Based Renormalization EffectsComments: 11 pages, 2 figures, 1 table (Supplementary Material: 8 pages, 3 figures), To be submitted to Physical Review BSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Other Condensed Matter (cond-mat.other)
The standard theory of Coulomb blockade [$P(E)$ theory] in ultra-small tunnel junctions has been formulated on the basis of phase-phase correlations by several authors. It was recently extended by several experimental and theoretical works to account for novel features ranging from time-reversal asymmetry to electromagnetic environment-based renormalization effects. Despite this progress, the theory remains elusive in the case of one dimensional arrays. Here, we apply path integral formalism to derive the Cooper-pair current and the BCS quasi-particle current in single small Josephson junctions and extend it to include long Josephson junction arrays as effective single junctions. We consider renormalization effects due to the electromagnetic environment in the single junction as well as the array. As is the case in the single junction, we find that the spectrum of applied oscillating electromagnetic fields is renormalized by the same complex-valued factor $\Xi(\omega) = |\Xi(\omega)|\exp i\eta(\omega)$ that modifies the environmental impedance in the $P(E)$ function. This factor acts as a linear response function for applied oscillating electromagnetic fields driving the quantum circuit, leading to a mass gap in the thermal spectrum of the electromagnetic field. The mass gap can be modeled as a pair of exotic particle excitation with quantum statistics determined by the argument $\eta(\omega)$. In the case of the array, this pair corresponds to a bosonic charge soliton/anti-soliton pair injected into the array by the electromagnetic field. Possible application of these results is in dynamical Coulomb blockade experiments where long arrays are used as electromagnetic power detectors.
- arXiv:1911.10976 (replaced) [pdf, ps, other]
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Title: Intermolecular Cross-Correlations in the Dielectric Response of GlycerolAuthors: Jan Philipp Gabriel, Parvaneh Zourchang, Florian Pabst, Andreas Helblingand, Peter Weigland, Till Böhmer, Thomas BlochowiczSubjects: Soft Condensed Matter (cond-mat.soft); Chemical Physics (physics.chem-ph)
We suggest a way to disentangle self- from cross-correlation contributions in the dielectric spectra of glycerol. Recently it was demonstrated for monohydroxy alcohols that a detailed comparison of the dynamic susceptibilities of photon correlation and broadband dielectric spectroscopy allows to unambiguously disentangle a collective relaxation mode known as the Debye process, which could arises due to supramolecular structures, and the $\alpha$-relaxation, which proves to be identical in both methods. In the present paper, we apply the same idea and analysis to the paradigmatic glass former glycerol. For that purpose we present new light scattering data from photon correlation spectroscopy measurements and combine these with literature data to obtain a data set covering a dynamic range from $10^{-4}-10^{13}\,$Hz. Then we apply the above mentioned analysis by comparing this data set with a corresponding set of broadband dielectric data. Our finding is that even in a polyalcohol self- and cross-correlation contributions can approximately be disentangled in that way and that the emerging picture is very similar to that in monohydroxy alcohols. This is further supported by comparing the data with fast field cycling NMR measurements and dynamic shear relaxation data from the literature, and it turns out that, within the described approach, the $\alpha$-process appears very similar in all methods, while the pronounced differences observed in the spectral density are due to a different expression of the slow collective relaxational contribution. In the dielectric spectra the strength of this peak is reasonably well estimated by the Kirkwood correlation factor, which supports the view that it arises due to dynamic cross-correlations, which were previously often assumed to be negligible in dielectric measurements.
- arXiv:1911.11978 (replaced) [pdf, other]
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Title: Non-Hermitian Floquet topological superconductors with multiple Majorana edge modesAuthors: Longwen ZhouComments: 15 pages, 7 figuresJournal-ref: Phys. Rev. B 101, 014306 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Quantum Physics (quant-ph)
Majorana edge modes are candidate elements of topological quantum computing. In this work, we purpose a Floquet engineering approach to generate arbitrarily many non-Hermitian Majorana zero and $\pi$ modes at the edges of a one-dimensional topological superconductor. Focusing on a Kitaev chain with periodically kicked superconducting pairings and gain/losses in the chemical potential or nearest neighbor hopping terms, we found rich non-Hermitian Floquet topological superconducting phases, which are originated from the interplay between drivings and non-Hermitian effects. Each of the phases is characterized by a pair of topological winding numbers, which can in principle take arbitrarily large integer values thanks to the applied driving fields. Under open boundary conditions, these winding numbers also predict the number of degenerate Majorana edge modes with quasienergies zero and $\pi$. Our findings thus expand the family of Floquet topological phases in non-Hermitian settings, with potential applications in realizing environmentally robust Floquet topological quantum computations.
- arXiv:1911.12206 (replaced) [pdf, ps, other]
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Title: Uncertainty relation for angle from a quantum-hydrodynamical perspectiveComments: 7 pages, no figure, discussions and references are addedJournal-ref: Ann. Phys. 416, 168159 (2020)Subjects: Quantum Physics (quant-ph); Statistical Mechanics (cond-mat.stat-mech); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Theory (hep-th)
We revisit the problem of the uncertainty relation for angle by using quantum hydrodynamics formulated in the stochastic variational method (SVM), where we need not define the angle operator. We derive both the Kennard and Robertson-Schroedinger inequalities for canonical variables in polar coordinates. The inequalities have state-dependent minimum values which can be smaller than \hbar/2 and then permit a finite uncertainty of angle for the eigenstate of the angular momentum. The present approach provides a useful methodology to study quantum behaviors in arbitrary canonical coordinates.
- arXiv:1911.12839 (replaced) [pdf, other]
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Title: Correlated dynamics of fermionic impurities induced by the counterflow of an ensemble of fermionsComments: 21 pages, 14 figuresJournal-ref: Phys. Rev. A 101, 053619 (2020)Subjects: Quantum Gases (cond-mat.quant-gas); Atomic Physics (physics.atom-ph); Quantum Physics (quant-ph)
We investigate the nonequilibrium quantum dynamics of a single and two heavy fermionic impurities being harmonically trapped and repulsively interacting with a finite ensemble of majority fermions. A quench of the potential of the majority species from a double-well to a harmonic trap is applied, enforcing its counterflow which in turn perturbs the impurities. For weak repulsions it is shown that the mixture undergoes a periodic mixing and demixing dynamics, while stronger interactions lead to a more pronounced dynamical spatial separation. In the presence of correlations the impurity exhibits an expansion dynamics which is absent in the Hartree-Fock case resulting in an enhanced degree of miscibility. We generalize our results to different impurity masses and demonstrate that the expansion amplitude of the impurity reduces for a larger mass. Furthermore, we showcase that the majority species is strongly correlated and a phase separation occurs on the two-body level. Most importantly, signatures of attractive impurity-impurity induced interactions mediated by the majority species are identified in the time-evolution of the two-body correlations of the impurities, a result that is supported by inspecting their spatial size.
- arXiv:1911.13184 (replaced) [pdf, other]
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Title: Excitons in Cu2O -- from Quantum Wells to Bulk Crystals and Additional Boundary Conditions for Rydberg Exciton-PolaritonsComments: 9 pages, 7 figuresJournal-ref: Phys. Rev. B 101, 205202 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Optics (physics.optics)
We propose a scheme for calculation of optical functions of a semiconductor with Rydberg excitons, for a wide interval of dimensions. We start with 2-dimensional structure, then going to thin films and ending on 3-dimensional bulk crystals. The calculations including the polaritons are performed, the case of large number of polariton branches is discussed and obtained theoretical absorption spectra show good agreement with experimental data.
- arXiv:1912.02952 (replaced) [pdf, other]
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Title: Hyperuniform monocrystalline structures by spinodal solid-state dewettingAuthors: Marco Salvalaglio, Mohammed Bouabdellaoui, Monica Bollani, Abdennacer Benali, Luc Favre, Jean-Benoit Claude, Jerome Wenger, Pietro de Anna, Francesca Intonti, Axel Voigt, Marco AbbarchiComments: 6 pages, 4 figures, supplementary information (7 pages) enclosedSubjects: Materials Science (cond-mat.mtrl-sci)
Materials featuring anomalous suppression of density fluctuations over large length scales are emerging systems known as disordered hyperuniform. The underlying hidden order renders them appealing for several applications, such as light management and topologically protected electronic states. These applications require scalable fabrication, which is hard to achieve with available top-down approaches. Theoretically it is known that spinodal decomposition can lead to disordered hyperuniform architectures. Spontaneous formation of stable patterns could thus be a viable path for the implementation of this peculiar class of materials via bottom-up approaches. We show that mono-crystalline semiconductor-based structures, in particular Si$_{1-x}$Ge$_{x}$ layers deposited on silicon-on-insulator substrates, can undergo spinodal solid-state dewetting and indeed lead to correlated disorder with an effective hyperuniform character. Nano- to micrometric sized structures targeting specific morphologies and hyperuniform character can be obtained, proving the generality of the approach and paving the way for technological applications of disordered hyperuniform metamaterials. Phase-field simulations explain the underlying non-linear dynamics and the physical origin of the emerging patterns.
- arXiv:1912.04907 (replaced) [pdf, other]
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Title: Particle-Hole Duality, Emergent Fermi Liquids and Fractional Chern Insulators in Moiré FlatbandsComments: 6+5 pages, 3+2 figures. PRL Editors' SuggestionJournal-ref: Phys. Rev. Lett. 124, 106803 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci); Strongly Correlated Electrons (cond-mat.str-el)
Moir\'e flatbands, occurring, e.g., in twisted bilayer graphene at magic angles, have attracted ample interest due to their high degree of experimental tunability and the intriguing possibility of generating novel strongly interacting phases. Here we consider the core problem of Coulomb interactions within fractionally filled spin and valley polarized Moir\'e flatbands and demonstrate that the dual description in terms of holes, which acquire a nontrivial hole dispersion, provides key physical intuition and enables the use of standard perturbative techniques for this strongly correlated problem. In experimentally relevant examples such as ABC stacked trilayer and twisted bilayer graphene aligned with boron nitride, it leads to emergent interaction-driven Fermi liquid states at electronic filling fractions down to around $1/3$ and $2/3$ respectively. At even lower filling fractions, the electron density still faithfully tracks the single-hole dispersion while exhibiting distinct non-Fermi liquid behavior. Most saliently, we provide microscopic evidence that high temperature fractional Chern insulators can form in twisted bilayer graphene aligned with hexagonal boron nitride.
- arXiv:1912.05367 (replaced) [pdf, other]
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Title: Robust cycloid crossover driven by anisotropy in the skyrmion host GaV$_\mathbf{4}$S$_\mathbf{8}$Authors: E. M. Clements, R. Das, G. Pokharel, M. H. Phan, A. D. Christianson, D. Mandrus, J. C. Prestigiacomo, M. S. Osofsky, H. SrikanthComments: 12 pages, 9 figures, minor figure corrections, expanded explanations in Secs. I & IIIB.,CJournal-ref: Phys. Rev. B 101, 094425 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci); Strongly Correlated Electrons (cond-mat.str-el)
We report on the anomalous magnetization dynamics of the cycloidally-modulated spin textures under the influence of uniaxial anisotropy in multiferroic $\mathrm{GaV_4S_8}$. The temperature and field dependence of the linear ac susceptibility [$\chi_{1\omega}^{\prime}(T,H)$], ac magnetic loss [$\chi_{1\omega}^{\prime\prime}(T,H)$], and nonlinear ac magnetic response [$M_{3\omega}(T,H)$] are examined across the magnetic phase diagram in the frequency range $f = 10-10000$ Hz. According to recent theory, skyrmion vortices under axial crystal symmetry are confined along specific orientations, resulting in enhanced robustness against oblique magnetic fields and altered spin dynamics. We characterize the magnetic response of each spin texture and find that the dynamic rigidity of the N\'eel skyrmion lattice appears enhanced compared to Bloch-type skyrmions in cubic systems, even in the multidomain state. Anomalous $M_{3\omega}$ and strong dissipation emerge over the same phase regime where strong variations in the cycloid pitch were observed on lowering temperature in recent small-angle neutron scattering experiments [White et al., Phys. Rev. B 97, 020401(R) (2018)]. Here, we show that strong anisotropy also drives an extended crossover of the zero-field cycloid texture in $\mathrm{GaV_4S_8}$. The frequency dependence of these dynamic signatures is consistent with that of a robust anharmonic spin texture exhibiting a correlated domain arrangement. The results underpin the essential role of magnetic anisotropy in enhancing the rigidity of topological spin textures for diverse applications.
- arXiv:1912.05916 (replaced) [pdf, other]
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Title: Deep-learning estimation of band gap with the reading-periodic-table method and periodic convolution layerAuthors: Tomohiko KonnoComments: 8 pages for bodySubjects: Machine Learning (cs.LG); Materials Science (cond-mat.mtrl-sci)
In this study, the deep learning method named reading periodic table, which utilizes deep learning to read the periodic table and the laws of the elements, was extended. The method now also learns the periodicity behind the periodic table, that is, the left- and right-most columns are adjacent to one another behind the table at the learning representation level. While the original method handles the table as it is, the extended method treats the periodic table as if its two edges are connected. This is achieved using novel layers named periodic convolution layers, which can handle inputs having periodicity and may be applied to other problems related to computer vision, time series, and so on if the data possesses some periodicity. In the reading periodic table method, no input of any material feature or descriptor is required. We verified that the method is also applicable for estimating the band gap of materials other than superconductors, for which the method was originally applied. We demonstrated two types of deep learning estimation: methods to estimate the existence of a band gap and those to estimate the value of the band gap given that the materials were known to have one. Finally, we discuss the limitations of the dataset and model evaluation method. We may be unable to distinguish good models based on the random train--test split scheme; thus, we must prepare an appropriate dataset where the training and test data are temporally separate.
- arXiv:1912.06549 (replaced) [pdf, ps, other]
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Title: Density functional theory for collisionless plasmas -- equivalence of fluid and kinetic approachesAuthors: Giovanni ManfrediComments: To appear in the Special Issue "The many facets of the Vlasov equation", published by the Journal of Plasma Physics, from the Vlasovia 2019 conference, Strasbourg, France, July 2019Subjects: Plasma Physics (physics.plasm-ph); Strongly Correlated Electrons (cond-mat.str-el)
Density functional theory (DFT) is a powerful theoretical tool widely used in such diverse fields as computational condensed matter physics, atomic physics, and quantum chemistry. DFT establishes that a system of $N$ interacting electrons can be described uniquely by its single-particle density $n(\boldsymbol{r})$, instead of the $N$-body wave function, yielding an enormous gain in terms of computational speed and memory storage space. Here, we use time-dependent DFT to show that a classical collisionless plasma can always, in principle, be described by a set of fluid equations for the single-particle density and current. The results of DFT guarantee that an exact closure relation, fully reproducing the Vlasov dynamics, necessarily exists, although it may be complicated (nonlocal in space and time, for instance) and difficult to obtain in practice. This goes against the common wisdom in plasma physics that the Vlasov and fluid descriptions are mutually incompatible, with the latter inevitably missing some "purely kinetic" effects.
- arXiv:1912.09078 (replaced) [pdf, other]
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Title: Floquet topological phases with fourfold-degenerate edge modes in a driven spin-1/2 Creutz ladderComments: 10 pages, 5 figuresJournal-ref: Phys. Rev. A 101, 033607 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Floquet engineering has the advantage of generating new phases with large topological invariants and many edge states by simple driving protocols. In this work, we propose an approach to obtain Floquet edge states with fourfold degeneracy and even-integer topological characterizations in a spinful Creutz ladder model, which is realizable in current experiments. Putting the ladder under periodic quenches, we found rich Floquet topological phases in the system, which belong to the symmetry class CII. Each of these phases is characterized by a pair of even integer topological invariants $(w_{0},w_{\pi}) \in 2\mathbb{Z} \times 2 \mathbb{Z}$, which can take arbitrarily large values with the increase of driving parameters. Under the open boundary condition, we further obtain multiple quartets of topological edge states with quasienergies zero and $\pi$ in the system. Their numbers are determined by the bulk topological invariants $(w_{0},w_{\pi})$ due to the bulk-edge correspondence. Finally, we propose a way to dynamically probe the Floquet topological phases in our system by measuring a generalized mean chiral displacement. Our findings thus enrich the family of Floquet topological matter, and put forward the detection of their topological properties.
- arXiv:1912.10930 (replaced) [pdf, other]
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Title: Nonlinear quasilocalized excitations in glasses. I. True representatives of soft spotsComments: 15 pages, 9 figures, accepted manuscriptJournal-ref: Phys. Rev. E 101, 032130 (2020)Subjects: Soft Condensed Matter (cond-mat.soft)
Structural glasses formed by quenching a melt possess a population of soft quasilocalized excitations --- often called `soft spots' --- that are believed to play a key role in various thermodynamic, transport and mechanical phenomena. Under a narrow set of circumstances, quasilocalized excitations assume the form of vibrational (normal) modes, that are readily obtained by a harmonic analysis of the multi-dimensional potential energy. In general, however, direct access to the population of quasilocalized modes via harmonic analysis is hindered by hybridizations with other low-energy excitations, e.g.~phonons. In this series of papers we re-introduce and investigate the statistical-mechanical properties of a class of low-energy quasilocalized modes --- coined here \emph{nonlinear quasilocalized excitations} (NQEs) --- that are defined via an anharmonic (nonlinear) analysis of the potential energy landscape of a glass, and do not hybridize with other low-energy excitations. In this first paper, we review the theoretical framework that embeds a micromechanical definition of NQEs. We demonstrate how harmonic quasilocalized modes hybridize with other soft excitations, whereas NQEs properly represent soft spots without hybridization. We show that NQEs' energies converge to the energies of the softest, non-hybridized harmonic quasilocalized modes, cementing their status as true representatives of soft spots in structural glasses. Finally, we perform a statistical analysis of the mechanical properties of NQEs, which results in a prediction for the distribution of potential energy barriers that surround typical inherent states of structural glasses, as well as a prediction for the distribution of local strain thresholds to plastic instability.
- arXiv:1912.10956 (replaced) [pdf, other]
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Title: Statistical physics of interacting proteins: impact of dataset size and quality assessed in synthetic sequencesComments: 18 pages, 16 figuresJournal-ref: Phys. Rev. E 101, 032413 (2020)Subjects: Biomolecules (q-bio.BM); Statistical Mechanics (cond-mat.stat-mech); Biological Physics (physics.bio-ph)
Identifying protein-protein interactions is crucial for a systems-level understanding of the cell. Recently, algorithms based on inverse statistical physics, e.g. Direct Coupling Analysis (DCA), have allowed to use evolutionarily related sequences to address two conceptually related inference tasks: finding pairs of interacting proteins, and identifying pairs of residues which form contacts between interacting proteins. Here we address two underlying questions: How are the performances of both inference tasks related? How does performance depend on dataset size and the quality? To this end, we formalize both tasks using Ising models defined over stochastic block models, with individual blocks representing single proteins, and inter-block couplings protein-protein interactions; controlled synthetic sequence data are generated by Monte-Carlo simulations. We show that DCA is able to address both inference tasks accurately when sufficiently large training sets are available, and that an iterative pairing algorithm (IPA) allows to make predictions even without a training set. Noise in the training data deteriorates performance. In both tasks we find a quadratic scaling relating dataset quality and size that is consistent with noise adding in square-root fashion and signal adding linearly when increasing the dataset. This implies that it is generally good to incorporate more data even if its quality is imperfect, thereby shedding light on the empirically observed performance of DCA applied to natural protein sequences.
- arXiv:1912.11923 (replaced) [pdf, other]
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Title: Spectral Fluctuations in the Sachdev-Ye-Kitaev ModelComments: An important typo correctedSubjects: High Energy Physics - Theory (hep-th); Statistical Mechanics (cond-mat.stat-mech)
We present a detailed quantitative analysis of spectral correlations in the Sachdev-Ye-Kitaev (SYK) model. We find that the deviations from universal Random Matrix Theory (RMT) behavior are due to a small number of long-wavelength fluctuations from one realization of the ensemble to the next one. These modes can be parameterized effectively in terms of Q-Hermite orthogonal polynomials, the main contribution being the scale fluctuations for which we give a simple estimate. Our numerical results for $N=32$ show that only the lowest eight polynomials are needed to eliminate the nonuniversal part of the spectral fluctuations. The covariance matrix of the coefficients of this expansion is obtained analytically from low-order double-trace moments. We evaluate the covariance matrix of the first six moments and find that it agrees with the numerics. We also analyze the spectral correlation using a nonlinear $\sigma$-model, which is derived through a Fierz transformation, and evaluate the one and two-point spectral correlator to two-loop order. The wide correlator is given by the sum of the universal RMT result and corrections whose lowest-order term corresponds to scale fluctuations. However, the loop expansion of the $\sigma$-model results in an ill-behaved expansion of the resolvent, and it gives universal RMT fluctuations not only for $q=4$ but also for the $q=2$ SYK model while the correct result in this case should have been Poisson statistics. We analyze the number variance and spectral form factor for $N=32$ and $q=4$ numerically. We show that the quadratic deviation of the number variance for large energies appears as a peak for small times in the spectral form factor. After eliminating the long-wavelength fluctuations, we find quantitative agreement with RMT up to an exponentially large number of level spacings or exponentially short times, respectively.
- arXiv:1912.12689 (replaced) [pdf]
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Title: Giant momentum-dependent spin splitting in centrosymmetric low Z antiferromagnetsComments: 20 pages, 5 figuresSubjects: Materials Science (cond-mat.mtrl-sci); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Quantum Physics (quant-ph)
The energy vs. crystal momentum E(k) diagram for a solid (band structure) constitutes the road map for navigating its optical, magnetic, and transport properties. By selecting crystals with specific atom types, composition and symmetries, one could design a target band structure and thus desired properties. A particularly attractive outcome would be to design energy bands that are split into spin components with a momentum-dependent splitting, as envisioned by Pekar and Rashba [Zh. Eksperim. i Teor. Fiz. 47 (1964)], enabling spintronic application. The current paper provides "design principles" for wavevector dependent spin splitting (SS) of energy bands that parallels the traditional Dresselhaus and Rashba spin-orbit coupling (SOC) - induce splitting, but originates from a fundamentally different source -- antiferromagnetism. We identify a few generic AFM prototypes with distinct SS patterns using magnetic symmetry design principles. These tools allow also the identification of specific AFM compounds with SS belonging to different prototypes. A specific compound -- centrosymmetric tetragonal MnF2 -- is used via density functional band structure calculations to quantitatively illustrate one type of AFM SS. Unlike the traditional SOC-induced effects restricted to non-centrosymmetric crystals, we show that antiferromagnetic-induced spin splitting broadens the playing field to include even centrosymmetric compounds, and gives SS comparable in magnitude to the best known ('giant') SOC effects, even without SOC, and consequently does not rely on the often-unstable high atomic number elements required for high SOC. We envision that use of the current design principles to identify an optimal antiferromagnet with spin-split energy bands would be beneficial for efficient spin-charge conversion and spin orbit torque applications without the burden of requiring compounds containing heavy elements.
- arXiv:2001.01671 (replaced) [pdf, other]
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Title: Entanglement spreading and quasiparticle picture beyond the pair structureComments: 15 pages; 7 figuresJournal-ref: SciPost Phys. 8, 045 (2020)Subjects: Statistical Mechanics (cond-mat.stat-mech); Strongly Correlated Electrons (cond-mat.str-el); Quantum Physics (quant-ph)
The quasi-particle picture is a powerful tool to understand the entanglement spreading in many-body quantum systems after a quench. As an input, the structure of the excitations' pattern of the initial state must be provided, the common choice being pairwise-created excitations. However, several cases exile this simple assumption. In this work, we investigate weakly-interacting to free quenches in one dimension. This results in a far richer excitations' pattern where multiplets with a larger number of particles are excited. We generalize the quasi-particle ansatz to such a wide class of initial states, providing a small-coupling expansion of the Renyi entropies. Our results are in perfect agreement with iTEBD numerical simulations.
- arXiv:2001.04613 (replaced) [pdf, other]
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Title: Spin splitting with persistent spin textures induced by the line defect in 1T-phase of monolayer transition metal dichalcogenidesComments: 5 figures, under reviewJournal-ref: Phys. Rev. B 101, 155410 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el)
The spin splitting driven by spin-orbit coupling in monolayer (ML) transition metal dichalcogenides (TMDCs) family has been widely studied only for the 1H-phase structure, while it is not profound for the 1T-phase structure due to the centrosymmetric of the crystal. Based on first-principles calculations, we show that significant spin splitting can be induced in the ML 1T-TMDCs by introducing the line defect. Taking the ML PtSe2 as a representative example, we considered the most stable form of the line defects, namely Se-vacancy line defect (Se-VLD). We find that large spin splitting is observed in the defect states of the Se-VLD, exhibiting a highly unidirectional spin configuration in the momentum space. This peculiar spin configuration may yield the so-called persistent spin textures (PST), a specific spin structure resulting in protection against spin-decoherence and supporting an extraordinarily long spin lifetime. Moreover, by using k.p perturbation theory supplemented with symmetry analysis, we clarified that the emerging of the spin splitting maintaining the PST in the defect states is originated from the inversion symmetry breaking together with one-dimensional nature of the Se-VLD engineered ML PtSe2. Our findings pave a possible way to induce the significant spin splitting in the ML 1T-TMDCs, which could be highly important for designing spintronic devices.
- arXiv:2002.01624 (replaced) [pdf, ps, other]
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Title: Quantum depletion density of a homogeneous dilute Bose gas within improved Hartree-Fock approximationAuthors: Nguyen Van ThuSubjects: Quantum Gases (cond-mat.quant-gas)
Motivated by the recent experiment [R. Lopes et. al., Phys. Rev. Lett. 119, 190404 (2017)] with a homogeneous Bose gas, we investigate a homogeneous dilute Bose gas to reproduce the quantum depletion density. By means of Cornwall-Jackiw-Tomboulis effective action approach within improved Hartree-Fock approximation, the quantum depletion density is recovered in an easier manner.Additionally, the higher-order terms are taken into account for the condensed fraction.
- arXiv:2002.03868 (replaced) [pdf, other]
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Title: Modeling and fabrication of chip-based superconducting traps for levitation of micrometer-sized superconducting particlesComments: 19 pages, 20 figuresSubjects: Applied Physics (physics.app-ph); Superconductivity (cond-mat.supr-con); Quantum Physics (quant-ph)
We describe the finite-element modeling and fabrication of chip-based superconducting traps for levitating micrometer-sized superconducting particles. Such experiments promise to lead to a new generation of macroscopic quantum experiments and of force and acceleration sensors. An accurate modeling of the utilized trap architectures is crucial for predicting parameters of the traps, such as trap stability, frequency and levitation height, in realistic situations accounting for the finite extent of the involved superconducting objects. To this end, we apply a modeling method that is applicable to arbitrary superconducting structures in the Meissner state. It is based on Maxwell-London equations in the static regime using the A-V formulation. The modeling allows us to simulate superconducting objects with arbitrary geometry subject to arbitrary magnetic field distributions and captures finite volume effects like magnetic field expulsion. We use this modeling to simulate two chip-based trap architectures: an anti-Helmholtz coil-type trap and a planar double-loop trap. We calculate important parameters of the superconducting traps for the cases of levitating micrometer-sized particles of either spherical, cylindrical or ring shape. We compare our modeling results to analytical test cases for idealized geometries. We also model detection of the motion of the levitated particle by measurement of flux-changes induced in a nearby pick-up loop. We demonstrate the fabrication of the analyzed chip-based traps and particles using thin Nb films. Our modeling is generic and has applications beyond the one considered, such as designing superconducting magnetic shields or for calculating filling factors in superconducting resonators.
- arXiv:2002.03908 (replaced) [pdf, other]
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Title: Giant electron-phonon coupling of the breathing plane oxygen phonons in the dynamic stripe phase of La$_{1.67}$Sr$_{0.33}$NiO$_4$Subjects: Strongly Correlated Electrons (cond-mat.str-el); Superconductivity (cond-mat.supr-con)
Doped antiferromagnets host a vast array of physical properties and learning how to control them is one of the biggest challenges of condensed matter physics. La$_{1.7}$Sr$_{0.3}$NiO$_4$ (LSNO) is a classic example of such a material. At low temperatures holes introduced via substitution of La by Sr segregate into lines to form boundaries between magnetically ordered domains in the form of stripes. The stripes become dynamic at high temperatures, but LSNO remains insulating presumably because an interplay between magnetic correlations and electron-phonon coupling localizes charge carriers. Magnetic degrees of freedom have been extensively investigated in this system, but phonons are almost completely unexplored. We searched for electron-phonon anomalies in LSNO by inelastic neutron scattering. Giant renormalization of plane Ni-O bond-stretching modes that modulate the volume around Ni appears on entering the dynamic charge stripe phase. Other phonons are a lot less sensitive to stripe melting. Dramatic overdamping of the breathing modes indicates that dynamic stripe phase may host small polarons. We argue that this feature sets electron-phonon coupling in nickelates apart from that in cuprates where breathing phonons are not overdamped and point out remarkable similarities with the colossal magnetoresistance (CMR) manganites.
- arXiv:2002.07157 (replaced) [pdf, other]
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Title: Neutron scattering off Weyl semimetalsComments: 23 pages and 11 figures, submitted to Physical Review X; acknowledgement updated, minor correctionsSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci); Strongly Correlated Electrons (cond-mat.str-el)
We present how to detect type-$1$ Weyl nodes in a material by inelastic neutron scattering. Such an experiment first of all allows one to determine the dispersion of the Weyl fermions. We extend the reasoning to produce a quantitative test of the Weyl equation taking into account realistic anisotropic properties. These anisotropies are mostly contained in the form of the emergent magnetic moment of the excitations, which determines how they couple to the neutron. Although there are many material parameters, we find several quantitative predictions that are universal and demonstrate that the excitations are described by solutions to the Weyl equation. The realistic, anisotropic coupling between electrons and neutrons implies that even fully unpolarized neutrons can reveal the spin-momentum locking of the Weyl fermions because the neutrons will couple to some components of the Weyl fermion pseudospin more strongly. On the other hand, in an experiment with polarized neutrons, the scattered neutron beam remains fully polarized in a direction that varies as a function of momentum transfer (within the range of validity of the Weyl equation). This allows measurement of the chirality of Weyl fermions for inversion symmetric nodes. Furthermore, we estimate that the scattering rate may be large enough for such experiments to be practical; in particular, the magnetic moment may be larger than the ordinary Bohr magneton, compensating for a small density of states.
- arXiv:2002.08713 (replaced) [pdf, other]
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Title: Carrier diffusion in GaN -- a cathodoluminescence study. I: Temperature-dependent generation volumeAuthors: Uwe Jahn, Vladimir M. Kaganer, Karl K. Sabelfeld, Anastasya E. Kireeva, Jonas Lähnemann, Carsten Pfüller, Caroline Chèze, Klaus Biermann, Raffaella Calarco, Oliver BrandtSubjects: Materials Science (cond-mat.mtrl-sci); Applied Physics (physics.app-ph)
The determination of the carrier diffusion length of semiconductors such as GaN and GaAs by cathodoluminescence imaging requires accurate knowledge about the spatial distribution of generated carriers. To obtain the lateral distribution of generated carriers for sample temperatures between 10 and 300 K, we utilize cathodoluminescence intensity profiles measured across single quantum wells embedded in thick GaN and GaAs layers. Thin (Al,Ga)N and (Al,Ga)As barriers, respectively, prevent carriers diffusing in the GaN and GaAs layers to reach the well, which would broaden the profiles. The experimental CL profiles are found to be systematically wider than the energy loss distributions calculated by means of the Monte Carlo program CASINO, with the width monotonically increasing with decreasing temperature. This effect is observed for both GaN and GaAs and becomes more pronounced for higher acceleration voltages. We discuss this phenomenon in terms of the electron-phonon interaction controlling the energy relaxation of hot carriers, and of the non-equilibrium phonon population created by this relaxation process. Finally, we present a phenomenological approach to simulate the carrier generation volume that can be used for the investigation of the temperature dependence of carrier diffusion.
- arXiv:2002.09397 (replaced) [pdf, other]
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Title: Relaxation and vibrational properties in metal alloys and other disordered systemsAuthors: Alessio ZacconeComments: Topical reviewJournal-ref: Journal of Physics: Condensed Matter 32, 203001 (2020)Subjects: Materials Science (cond-mat.mtrl-sci); Disordered Systems and Neural Networks (cond-mat.dis-nn); Soft Condensed Matter (cond-mat.soft); Statistical Mechanics (cond-mat.stat-mech)
The relaxation dynamics and the vibrational spectra of amorphous solids, such as metal alloys, have been intensely investigated as well separated topics in the past. The aim of this review is to summarize recent results in both these areas in an attempt to establish, or unveil, deeper connections between the two phenomena of relaxation and vibration. Theoretical progress in the area of slow relaxation dynamics of liquid and glassy systems and in the area of vibrational spectra of glasses and liquids is reviewed. After laying down a generic modelling framework to connect vibration and relaxation, the physics of metal alloys is considered where the emergence of power-law exponents has been identified both in the vibrational density of states (VDOS) as well as in density correlations. Also, theoretical frameworks which connect the VDOS to the relaxation behaviour and mechanical viscoelastic response in metallic glasses are reviewed. The same generic interpretative framework is then applied to the case of molecular glass formers where the emergence of stretched-exponential relaxation in dielectric relaxation can be put in quantitative relation with the VDOS by means of memory-function approaches. Further connections between relaxation and vibration are provided by the study of phonon linewidths in liquids and glasses, where a natural starting point is given by hydrodynamic theories. Finally, an agenda of outstanding issues including the appearance of compressed exponential relaxation in the intermediate scattering function of experimental and simulated systems (metal alloys, colloidal gels, jammed packings) is presented in light of available (or yet to be developed) mathematical models, and compared to non-exponential behaviour measured with macroscopic means such as mechanical spectroscopy/rheology.
- arXiv:2002.11345 (replaced) [pdf, other]
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Title: Jordan-Wigner Dualities for Translation-Invariant Hamiltonians in Any Dimension: Emergent Fractons that are FermionsAuthors: Nathanan TantivasadakarnComments: 27 pages, 4 figures, 7 tables. v2: references and clarifications added & misprints fixedSubjects: Strongly Correlated Electrons (cond-mat.str-el); Statistical Mechanics (cond-mat.stat-mech); High Energy Physics - Theory (hep-th); Mathematical Physics (math-ph); Quantum Physics (quant-ph)
Inspired by recent developments generalizing Jordan-Wigner dualities to higher dimensions, we develop a framework for such dualities for translation-invariant Hamiltonians using the algebraic formalism proposed by Haah. We prove that given a translation-invariant fermionic system with general $q$-body interactions, where $q$ is even, a local mapping preserving global fermion parity to a dual Pauli spin model exists and is unique up to a choice of basis. Furthermore, the dual spin model is constructive, and we present various examples of these dualities. As an application, we bosonize fermionic systems where fermion parity is also conserved on submanifolds such as higher-form, line, planar or fractal symmetry. For some cases in 3+1D, bosonizing such system can give rise to fracton models where the emergent particles are immobile, but yet can behave in certain ways like fermions. These models may be examples of new non-relativistic 't Hooft anomalies. Furthermore, fermionic subsystem symmetries are also present in various Majorana stabilizer codes, such as the color code or the checkerboard model, and we give examples where their duals are cluster states or new fracton models distinct from their doubled CSS codes.
- arXiv:2002.12059 (replaced) [pdf, other]
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Title: Quantum-heat fluctuation relations in $3$-level systems under projective measurementsComments: 12 Pages, 6 Figures. Contribution to the Special Issue "Many Body Quantum Chaos" in honour of Shmuel Fishman, published in the journal "Condensed Matter"Journal-ref: Condens. Matter 5 (1), 17 (2020)Subjects: Quantum Physics (quant-ph); Statistical Mechanics (cond-mat.stat-mech)
We study the statistics of energy fluctuations in a three-level quantum system subject to a sequence of projective quantum measurements. We check that, as expected, the quantum Jarzynski equality holds provided that the initial state is thermal. The latter condition is trivially satisfied for two-level systems, while this is generally no longer true for $N$-level systems, with $N > 2$. Focusing on three-level systems, we discuss the occurrence of a unique energy scale factor $\beta_{\rm eff}$ that formally plays the role of an effective inverse temperature in the Jarzynski equality. To this aim, we introduce a suitable parametrization of the initial state in terms of a thermal and a non-thermal component. We determine the value of $\beta_{\rm eff}$ for a large number of measurements and study its dependence on the initial state. Our predictions could be checked experimentally in quantum optics.
- arXiv:2002.12140 (replaced) [pdf, other]
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Title: Likely striping in stochastic nematic elastomersJournal-ref: Mathematics and Mechanics of Solids 2020Subjects: Soft Condensed Matter (cond-mat.soft)
For monodomain nematic elastomers, we construct generalised elastic-nematic constitutive models combining purely elastic and neoclassical-type strain-energy densities. Inspired by recent developments in stochastic elasticity, we extend these models to stochastic-elastic-nematic forms where the model parameters are defined by spatially-independent probability density functions at a continuum level. To investigate the behaviour of these systems and demonstrate the effects of the probabilistic parameters, we focus on the classical problem of shear striping in a stretched nematic elastomer for which the solution is given explicitly. We find that, unlike in the neoclassical case where the inhomogeneous deformation occurs within a universal interval that is independent of the elastic modulus, for the elastic-nematic models, the critical interval depends on the material parameters. For the stochastic extension, the bounds of this interval are probabilistic, and the homogeneous and inhomogeneous states compete in the sense that both have a a given probability to occur. We refer to the inhomogeneous pattern within this interval as "likely striping".
- arXiv:2002.12286 (replaced) [pdf]
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Title: Ultra-uniform Nanocrystalline Materials via Two-Step SinteringSubjects: Materials Science (cond-mat.mtrl-sci)
Nanocrystalline metals and ceramics with <100 nm grain sizes and superior properties are of great interest. Much has been discussed about achieving nano grains, but little is known about maintaining grain-size uniformity that is critical for material reliability. An especially intriguing question is whether it is possible to achieve a size distribution narrower than the one theoretically predicted by Hillert1 for normal grain growth, a possibility suggested (for growth with a higher growth exponent) by the generalized growth theory2 unifying the mean-field models of Lifshitz, Slyozov, Wagner (LSW)3,4 and Hillert. We show that this can be realized in an appropriately designed two-step sintering route that (a) takes advantage of the large growth exponent in the intermediate sintering stage to form an ultra-uniform porous microstructure, and (b) freezes the grain growth thereon while continuing densification to reach a full density. The resultant dense Al2O3 ceramic has an average grain size of 34 nm and a much narrower size distribution than predicted by Hillert.
- arXiv:2003.02624 (replaced) [pdf, other]
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Title: Synchronization of Coupled Oscillators -- Phase Transitions and EntropiesComments: 22 pages, 5 figures. To appear as book chapter in Springer's Understanding Complex SystemsSubjects: Statistical Mechanics (cond-mat.stat-mech)
Over the last half century the liquid-gas phase transition and the magnetization phase transition have come to be well understood. After an order parameter, $r$, is defined, it can be derived how $r=0$ for $T>T_c$ and how $r \propto (T_c - T)^\gamma$ at lowest order for $T < T_c$. The value of $\gamma$ appears to not depend on physical details of the system, but very much on dimensionality. No phase transitions exist for one-dimensional systems. For systems of four or more dimensions, each unit is interacting with sufficiently many neighbors to warrant a mean-field approach. The mean-field approximation leads to $\gamma = 1/2$. In this article we formulate a realistic system of coupled oscillators. Each oscillator moves forward through a cyclic 1D array of $n$ states and the rate at which an oscillator proceeds from state $i$ to state $i+1$ depends on the populations in states $i+1$ and $i-1$. We study how the phase transitions occur from a homogeneous distribution over the states to a clustered distribution. A clustered distribution means that oscillators have synchronized. We define an order parameter and we find that the critical exponent takes on the mean-field value of 1/2 for any $n$. However, as the number of states increases, the phase transition occurs for ever smaller values of $T_c$. We present rigorous mathematics and simple approximations to develop an understanding of the phase transitions in this system. We explain why and how the critical exponent value of 1/2 is expected to be robust and we discuss a wet-lab experimental setup to substantiate our findings.
- arXiv:2003.02806 (replaced) [pdf, other]
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Title: Universal motion of mirror-symmetric microparticles in confined Stokes flowAuthors: Rumen N. Georgiev, Sara O. Toscano, William E. Uspal, Bram Bet, Sela Samin, Rene van Roij, Huseyin Burak EralComments: 10 pages, 4 figures, 1 table, 1 PDF file containing Supplementary Text, Figures and TableSubjects: Fluid Dynamics (physics.flu-dyn); Soft Condensed Matter (cond-mat.soft)
Comprehensive understanding of particle motion in microfluidic devices is essential to unlock novel technologies for shape-based separation and sorting of microparticles like microplastics, cells and crystal polymorphs. Such particles interact hydrodynamically with confining surfaces, thus altering their trajectories. These hydrodynamic interactions are shape-dependent and can be tuned to guide a particle along a specific path. We produce strongly confined particles with various shapes in a shallow microfluidic channel via stop flow lithography. Regardless of their exact shape, particles with a single mirror plane have identical modes of motion: in-plane rotation and cross-stream translation along a bell-shaped path. Each mode has a characteristic time, determined by particle geometry. Furthermore, each particle trajectory can be scaled by its respective characteristic times onto two master curves. We propose minimalistic relations linking these timescales to particle shape. Together these master curves yield a trajectory universal to particles with a single mirror plane.
- arXiv:2003.03126 (replaced) [pdf, ps, other]
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Title: Metastability in the Potts model: exact results in the large q limitComments: 29 pages, 8 figuresSubjects: Statistical Mechanics (cond-mat.stat-mech)
We study the metastable equilibrium properties of the Potts model with heat-bath transition rates using a novel expansion. The method is especially powerful for large number of state spin variables and it is notably accurate in a rather wide range of temperatures around the phase transition.
- arXiv:2003.03890 (replaced) [pdf, ps, other]
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Title: Bending-induced director reorientation in a nematic liquid crystal elastomer bonded to a hyperelastic substrateComments: 15 pages, 4 figuresSubjects: Soft Condensed Matter (cond-mat.soft)
In this paper, the two-dimensional pure bending of a hyperelastic substrate coated by a nematic liquid crystal elastomer (abbreviated as NLCE) is studied within the framework of nonlinear elasticity. The governing system, arising from the deformational momentum balance, the orientational momentum balance and the mechanical constraint, is formulated, and the corresponding exact solution is derived for a given constitutive model. It is found that there exist two different bending solutions. In order to determine which the preferred one is, we compare the total potential energy for both solutions and find that the two energy curves may have an intersection point at a critical value of the bending angle $\alpha_c$ for some material parameters. In particular, the director $\bm n$ abruptly rotates $\dfrac{\pi}{2}$ from one solution to another at $\alpha_c$, which indicates a director reorientation (or jump). Furthermore, the effects of different material and geometric parameters on the bending deformation and the transition angle $\alpha_c$ can be revealed using the obtained bending solutions. Meanwhile, the exact solution can offer a benchmark problem for validating the accuracy of approximated plate models for liquid crystal elastomers.
- arXiv:2003.04162 (replaced) [pdf, ps, other]
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Title: Phenomenological theory in reentrant uranium-based superconductorsComments: 4 pages, 3 figure, +appendixSubjects: Superconductivity (cond-mat.supr-con); Materials Science (cond-mat.mtrl-sci); Strongly Correlated Electrons (cond-mat.str-el)
We develop a phenomenological theory for the family of uranium-based heavy fermion superconductors ($URhGe$, $UCoGe$, and $UTe_2$ ). The theory unifies the understanding of both superconductivity(SC) with a weak magnetic field and reentrant superconductivity(RSC) that appears at the first-order transition line with a high magnetic field. It is shown that the magnetizations along the easy and hard axis have opposite effects on superconductivity. The RSC is induced by the fluctuation parallel to the direction of the magnetic field. The theory makes specific predictions about the variation of triplet superconductivity order parameters $\vec{d}$ with applied external magnetic fields and the existence of a metastable state for the appearance of the RSC.
- arXiv:2003.05297 (replaced) [pdf, other]
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Title: Microscopic origin of molecule excitation via inelastic electron scattering in scanning tunneling microscopeSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Quantum Physics (quant-ph)
The scanning-tunneling-microscope-induced luminescence emerges recently as an incisive tool to measure the molecular properties down to the single-molecule level. The rapid experimental progress is far ahead of the theoretical effort to understand the observed phenomena. Such incompetence leads to a significant difficulty in quantitatively assigning the observed feature of the fluorescence spectrum to the structure and dynamics of a single molecule. This letter is devoted to reveal the microscopic origin of the molecular excitation via inelastic scattering of the tunneling electrons in scanning tunneling microscope. The current theory explains the observed large photon counting asymmetry between the molecular luminescence intensity at positive and negative bias voltage.
- arXiv:2003.05638 (replaced) [pdf, other]
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Title: Floquet and Anomalous Floquet Weyl SemimetalsSubjects: Strongly Correlated Electrons (cond-mat.str-el); Atomic Physics (physics.atom-ph)
The periodic driving of a quantum system can enable new topological phases without analogs in static systems. This provides a route towards preparing non-equilibrium quantum phases rooted into the non-equilibrium nature by periodic driving engineering. Motivated by the ongoing considerable interest in topological semimetals, we are interested in the novel topological phases in the periodically driven topological semimetals without a static counterpart. We propose to design non-equilibrium topological semimetals in the regime of weakly driving field where the spectrum width of shares the same magnitude with the driving frequency. We identify two novel types of non-equilibrium Weyl semimetals (i.e., Floquet and anomalous Floquet Weyl semimetals) that do not exhibit analogues in equilibrium. The proposed setup is shown to be experimentally feasible using the state-of-the-art techniques used to control ultracold atoms in optical lattices.
- arXiv:1411.7822 (replaced) [pdf, ps, other]
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Title: Taming Lévy flights in confined crowded geometriesComments: 9 pages, 10 figuresJournal-ref: J. Phys. Chem. 142, 164904 (2015)Subjects: Chemical Physics (physics.chem-ph); Statistical Mechanics (cond-mat.stat-mech)
We study a two-dimensional diffusive motion of a tracer particle in restricted, crowded anisotropic geometries. The underlying medium is the same as in our previous work [J. Chem. Phys. 140, 044706 (2014)] in which standard, gaussian diffusion was studied. Here, a tracer is allowed to perform Cauchy random walk with uncorrelated steps. Our analysis shows that presence of obstacles significantly influences motion, which in an obstacle-free space would be of a superdiffusive type. At the same time, the selfdiffusive process reveals different anomalous properties, both at the level of a single trajectory realization and after the ensemble averaging. In particular, due to obstacles, the sample mean squared displacement asymptotically grows sublinearly in time, suggesting non-Markov character of motion. Closer inspection of survival probabilities indicates however that underlying diffusion is memoryless over long time scales despite strong inhomogeneity of motion induced by orientational ordering.
- arXiv:1711.05752 (replaced) [pdf, other]
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Title: Quantum Origami: Transversal Gates for Quantum Computation and Measurement of Topological OrderComments: 11 pages + 8 pages of Appendices, 7 figures. A new section about the connection between transversal gates and symmetry-enriched topological orders has been addedJournal-ref: Phys. Rev. Research 2, 013285 (2020)Subjects: Quantum Physics (quant-ph); Quantum Gases (cond-mat.quant-gas); Strongly Correlated Electrons (cond-mat.str-el); High Energy Physics - Theory (hep-th)
In topology, a torus remains invariant under certain non-trivial transformations known as modular transformations. In the context of topologically ordered quantum states of matter, these transformations encode the braiding statistics and fusion rules of emergent anyonic excitations and thus serve as a diagnostic of topological order. Moreover, modular transformations of higher genus surfaces, e.g. a torus with multiple handles, can enhance the computational power of a topological state, in many cases providing a universal fault-tolerant set of gates for quantum computation. However, due to the intrusive nature of modular transformations, which abstractly involve global operations and manifold surgery, physical implementations of them in local systems have remained elusive. Here, we show that by folding manifolds, modular transformations can be applied in a single shot by independent local unitaries, providing a novel class of transversal logic gates for fault-tolerant quantum computation. Specifically, we demonstrate that multi-layer topological states with appropriate boundary conditions and twist defects allow modular transformations to be effectively implemented by a finite sequence of local SWAP gates between the layers. We further provide methods to directly measure the modular matrices, and thus the fractional statistics of anyonic excitations, providing a novel way to directly measure topological order.
- arXiv:1712.08229 (replaced) [pdf, other]
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Title: A compact broadband terahertz range quarter-wave plateComments: 6 pages, 4 figuresJournal-ref: J Infrared Milli Terahz Waves (2020)Subjects: Instrumentation and Detectors (physics.ins-det); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Applied Physics (physics.app-ph); Optics (physics.optics)
We detail the design and characterization of a terahertz range achromatic quarter-wave plate based on a stack of aligned variable thickness birefringent sapphire discs. The disc thicknesses and relative rotations of the discs are determined through a basin-hopping Monte Carlo thermal annealing routine. The basin-hopping scheme allows an improved refinement of the required thicknesses and rotations to give a predicted phase error from the ideal $\pi/2$ of only $0.5 \%$, which is a factor of approximately 6 better than previous efforts. Moreover, the large contrast between extraordinary and ordinary axes of sapphire allow us to greatly decrease the overall optical path length of our wave plate design by approximately a factor of 10 over similar designs based on quartz discs. However, this very same contrast requires very precise tolerances in the milled thicknesses of the discs and their assembly. We detail a method to compensate for differences in the thickness from their calculated ideal values. We have constructed one of our designs and found it similar in performance to other configurations, but with our much more compact geometry.
- arXiv:1803.09234 (replaced) [pdf, ps, other]
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Title: Tetrads in solids: from elasticity theory to topological quantum Hall systems and Weyl fermionsComments: 20 pages, no figures, prepared to issue of JETP devoted to 85 years of Lev Petrovich Pitaevskii, revised after referee report, difference between the Weyl tetrads and elasticity tetrads is clarifiedJournal-ref: JETP 127, 948-957 (2018)Subjects: Strongly Correlated Electrons (cond-mat.str-el)
Theory of elasticity in topological insulators has many common features with relativistic quantum fields interacting with gravitational field in the tetrad form. Here we discuss several issues in the effective topological (pseudo)electromagnetic response in three-dimensional weak crystalline topological insulators with no time-reversal symmetry that feature elasticity tetrads, including a mixed "axial-gravitational" anomaly. This response has some resemblance to "quasitopological" terms proposed for massless Weyl quasiparticles with separate, emergent fermion tetrads. As an example, we discuss the chiral/axial anomaly in superfluid 3He-A. We demonstrate the principal difference between the elasticity tetrads and the Weyl fermion tetrads in the construction of the topological terms in the action. In particular, the topological action expressed in terms of the elasticity tetrads, cannot be expressed in terms of the Weyl fermion tetrads since in this case the gauge invariance is lost.
- arXiv:1805.03182 (replaced) [pdf, other]
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Title: Deriving hydrodynamic equations from dry active matter models in three dimensionsComments: 40 pages, 14 figures, comments are welcomeJournal-ref: Journal of Statistical Mechanics: Theory and Experiment 2018 (9), 093202Subjects: Soft Condensed Matter (cond-mat.soft); Statistical Mechanics (cond-mat.stat-mech)
We derive hydrodynamic equations from Vicsek-style dry active matter models in three dimensions (3D), building on our experience on the 2D case using the Boltzmann-Ginzburg-Landau approach. The hydrodynamic equations are obtained from a Boltzmann equation expressed in terms of an expansion in spherical harmonics. All their transport coefficients are given with explicit dependences on particle-level parameters. The linear stability analysis of their spatially-homogeneous solutions is presented. While the equations derived for the polar case (original Vicsek model with ferromagnetic alignment) and their solutions do not differ much from their 2D counterparts, the active nematics case exhibits remarkable differences: we find a true discontinuous transition to order with a bistability region, and cholesteric solutions whose stability we discuss.
- arXiv:1810.04447 (replaced) [pdf, other]
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Title: 50 years in the Landau Institute environmentAuthors: G.E. VolovikComments: 23 pages, 20 figures, article dedicated to the 100th anniversary of KhalatninkovJournal-ref: Physics-Uspekhi 62, 1031-1045 (2019)Subjects: History and Philosophy of Physics (physics.hist-ph); Other Condensed Matter (cond-mat.other); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Phenomenology (hep-ph)
It is impossible to review all the fundamental works of Landau Institute, which made important contribution to physics in general. Here I will discuss only a part of these works, only those which directly influence my own work during 50 years (1968-2018). Khalatnikov created the unique Institute, where practically all important areas of theoretical physics have been represented, opening broad possibilities for collaboration. The multidisciplinary environment of the Landau Institute was the main element of inspiration.
- arXiv:1812.09183 (replaced) [pdf, other]
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Title: Classification of Matrix-Product Unitaries with SymmetriesComments: 6+16 pages, 3+8 figuresJournal-ref: Phys. Rev. Lett. 124, 100402 (2020)Subjects: Quantum Physics (quant-ph); Disordered Systems and Neural Networks (cond-mat.dis-nn); Statistical Mechanics (cond-mat.stat-mech); Strongly Correlated Electrons (cond-mat.str-el); Mathematical Physics (math-ph)
We prove that matrix-product unitaries (MPUs) with on-site unitary symmetries are completely classified by the (chiral) index and the cohomology class of the symmetry group $G$, provided that we can add trivial and symmetric ancillas with arbitrary on-site representations of $G$. If the representations in both system and ancillas are fixed to be the same, we can define symmetry-protected indices (SPIs) which quantify the imbalance in the transport associated to each group element and greatly refines the classification. These SPIs are stable against disorder and measurable in interferometric experiments. Our results lead to a systematic construction of two-dimensional Floquet symmetry-protected topological (SPT) phases beyond the standard classification, and thus shed new light on understanding nonequilibrium phases of quantum matter.
- arXiv:1901.11363 (replaced) [pdf, ps, other]
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Title: Gross-Pitaevskii Limit of a Homogeneous Bose Gas at Positive TemperatureJournal-ref: Archive for Rational Mechanics and Analysis, 236(3), 1217-1271 (2020)Subjects: Mathematical Physics (math-ph); Quantum Gases (cond-mat.quant-gas)
We consider a dilute, homogeneous Bose gas at positive temperature. The system is investigated in the Gross-Pitaevskii (GP) limit, where the scattering length $a$ is so small that the interaction energy is of the same order of magnitude as the spectral gap of the Laplacian, and for temperatures that are comparable to the critical temperature of the ideal gas. We show that the difference between the specific free energy of the interacting system and the one of the ideal gas is to leading order given by $4 \pi a \left( 2 \varrho^2 - \varrho_0^2 \right)$. Here $\varrho$ denotes the density of the system and $\varrho_0$ is the expected condensate density of the ideal gas. Additionally, we show that the one-particle density matrix of any approximate minimizer of the Gibbs free energy functional is to leading order given by the one of the ideal gas. This in particular proves Bose-Einstein condensation with critical temperature given by the one of the ideal gas to leading order. One key ingredient of our proof is a novel use of the Gibbs variational principle that goes hand in hand with the c-number substitution.
- arXiv:1902.07584 (replaced) [pdf, other]
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Title: Comment to the CPT-symmetric Universe: Two possible extensionsAuthors: G.E. VolovikComments: 2 pages, 1 figure, comment to PRL 121, 251301 (2018), accepted in JETP LettersJournal-ref: JETP Lett. 109, 682-683 (2019)Subjects: General Relativity and Quantum Cosmology (gr-qc); Other Condensed Matter (cond-mat.other); High Energy Physics - Phenomenology (hep-ph)
In Ref.1 (L. Boyle, K. Finn and N. Turok, CPT-Symmetric Universe, Phys. Rev. Lett. {\bf 121}, 251301 (2018)) the antispacetime Universe was suggested as the analytic continuation of our Universe across the Big Bang singularity in conformal time. We consider two different scenarios of analytic continuation. In one of them the analytic continuation is extended to the temperature of the system. This extension suggests that if such analytic continuation is valid, then it is possible that the initial stage of the evolution of the Universe on our side of the Big Bang was characterized by the negative temperature. In the second scenario, the analytic continuation is considered in the proper time. In this scenario the Big Bang represents the bifurcation point at which the $Z_2$ symmetry between the spacetime and antispacetime is spontaneously broken.
- arXiv:1903.01367 (replaced) [pdf]
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Title: Measuring valley polarization in two-dimensional materials with second-harmonic spectroscopyAuthors: Yi Wei Ho, Henrique Guimarães Rosa, Ivan Verzhbitskiy, Manuel Jose de Lima Ferreira Rodrigues, Takashi Taniguchi, Kenji Watanabe, Goki Eda, Vitor Manuel Pereira, José Carlos Viana GomesSubjects: Optics (physics.optics); Materials Science (cond-mat.mtrl-sci)
A population imbalance at different valleys of an electronic system lowers its effective rotational symmetry. We introduce a technique to measure such imbalance - a valley polarization - that exploits the unique fingerprints of this symmetry reduction in the polarization-dependent second-harmonic generation (SHG). We present the principle and detection scheme in the context of hexagonal two-dimensional crystals, which include graphene-based systems and the family of transition metal dichalcogenides, and provide a direct experimental demonstration using a 2H-MoSe$_{2}$ monolayer at room temperature. We deliberately use the simplest possible setup, where a single pulsed laser beam simultaneously controls the valley imbalance and tracks the SHG process. We further developed a model of the transient population dynamics which analytically describes the valley-induced SHG rotation in very good agreement with the experiment. In addition to providing the first experimental demonstration of the effect, this work establishes a conceptually simple, com-pact and transferable way of measuring instantaneous valley polarization, with direct applicability in the nascent field of valleytronics.
- arXiv:1903.02418 (replaced) [pdf, other]
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Title: Two roads to antispacetime in polar distorted B phase: Kibble wall and half-quantum vortexAuthors: G.E. VolovikComments: 4 pages, 1 figure, version submitted to JETP LettersJournal-ref: JETP Lett. 109, 499 (2019)Subjects: Other Condensed Matter (cond-mat.other); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Phenomenology (hep-ph)
We consider the emergent tetrad gravity and the analog of antispacetime realized in the recent experiments ( J.T. Makinen, et al., Nat. Comm. 10, 237 (2019)) on the composite defects in superfluid $^3$He: the Kibble walls bounded by strings (the half quantum vortices). The antispacetime can be reached in two different ways: by the "safe" route around the Alice string or by dangerous route across the Kibble wall. This consideration also suggests the scenario of the formation of the discrete symmetry -- the parity $P$ in Dirac equations -- from the continuous symmetry existing on the more fundamental level.
- arXiv:1904.01756 (replaced) [pdf, other]
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Title: Atomic-level Characterisation of Quantum Computer Arrays by Machine LearningComments: 8 pages, 4 figures and a supplementary information documentJournal-ref: npj Computational Materials 6, 19, 2020Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Data Analysis, Statistics and Probability (physics.data-an); Quantum Physics (quant-ph)
Atomic level qubits in silicon are attractive candidates for large-scale quantum computing, however, their quantum properties and controllability are sensitive to details such as the number of donor atoms comprising a qubit and their precise location. This work combines machine learning techniques with million-atom simulations of scanning-tunnelling-microscope (STM) images of dopants to formulate a theoretical framework capable of determining the number of dopants at a particular qubit location and their positions with exact lattice-site precision. A convolutional neural network was trained on 100,000 simulated STM images, acquiring a characterisation fidelity (number and absolute donor positions) of above 98\% over a set of 17,600 test images including planar and blurring noise. The method established here will enable a high-precision post-fabrication characterisation of dopant qubits in silicon, with high-throughput potentially alleviating the requirements on the level of resource required for quantum-based characterisation, which may be otherwise a challenge in the context of large qubit arrays for universal quantum computing.
- arXiv:1904.11516 (replaced) [pdf, other]
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Title: Meron Spin Textures in Momentum SpaceComments: 5 pages, 4 figuresJournal-ref: Phys. Rev. Lett. 124, 106103 (2020)Subjects: Optics (physics.optics); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We reveal the meron and antimeron spin textures in momentum space in a photonic crystal slab. These spin textures in momentum space have not been previously noted either in electronic or photonic systems. Breaking the inversion symmetry of a honeycomb photonic crystal gaps out the Dirac cones at the corners of Brillouin zone. The spin textures of photonic bands near the gaps exhibit a meron or antimeron. Unlike the electronic systems, the spin texture of the photonic modes manifests directly in the polarization of the leakage radiation, as the Dirac points can be above the light line. The spin texture provides a direct approach to visualize the local Berry curvature. Our work highlights the significant opportunities of using photonic structures for the exploration of topological spin textures, with potential applications towards topologically robust ways to manipulate polarizations and other modal characteristics of light.
- arXiv:1907.11026 (replaced) [pdf, other]
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Title: Free fermion representation of the topological surface codeAuthors: Ashk FarjamiComments: 12 pages, 4 figuresJournal-ref: Eur. Phys. J. B, 93 3 (2020) 42Subjects: Quantum Physics (quant-ph); Strongly Correlated Electrons (cond-mat.str-el)
The toric code is known to be equivalent to free fermions. This paper presents explicit local unitary transformations that map the $\mathbb{Z}_2$ toric and surface code --- the open boundary equivalent of the toric code --- to fermions. Through this construction it is shown that the surface code can be mapped to a set of free fermion modes, while the toric code requires additional fermionic symmetry operators. Finally, it is demonstrated how the anyonic statistics of these codes are encoded in the fermionic representations.
- arXiv:1907.11515 (replaced) [pdf, other]
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Title: Flat band and Planckian metalAuthors: G.E. VolovikComments: 2 pages, 1 figure, accepted in JETP LettersJournal-ref: JETP Lett. 110, 352-353 (2019)Subjects: Strongly Correlated Electrons (cond-mat.str-el)
We discuss the recent extension of the Sachdev-Ye-Kitaev (SYK) microscopic model by Patel and Sachdev in arXiv:1906.03265, which demonstrates the characteristic features of the Khodel-Shaginyan fermion condensate -- the existence of the finite region of momenta, where the energy of electrons is exactly zero (the flat band). The microscopic derivation of the flat band in this interacting model supports the original idea of Khodel and Shaginyan based on the phenomenological approach. It also suggests that it is the flat band, which is responsible for the linear dependence of resistivity on temperature in "strange metals".
- arXiv:1908.02091 (replaced) [pdf, ps, other]
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Title: Infinitesimal asphericity changes the universality of the jamming transitionComments: 17 pages, 7 figuresJournal-ref: J. Stat. Mech. (2020) 033302Subjects: Soft Condensed Matter (cond-mat.soft); Statistical Mechanics (cond-mat.stat-mech)
The jamming transition of non-spherical particles is fundamentally different from the spherical case. Non-spherical particles are hypostatic at their jamming points, while isostaticity is ensured in the case of the jamming of spherical particles. This structural difference implies that the presence of asphericity affects the critical exponents related to the contact number and the vibrational density of states. Moreover, while the force and gap distributions of isostatic jamming present power-law behaviors, even an infinitesimal asphericity is enough to smooth out these singularities. In a recent work [PNAS 115(46), 11736], we have used a combination of marginal stability arguments and the replica method to explain these observations. We argued that systems with internal degrees of freedom, like the rotations in ellipsoids, or the variation of the radii in the case of the \textit{breathing} particles fall in the same universality class. In this paper, we review comprehensively the results about the jamming with internal degrees of freedom in addition to the translational degrees of freedom. We use a variational argument to derive the critical exponents of the contact number, shear modulus, and the characteristic frequencies of the density of states. Moreover, we present additional numerical data supporting the theoretical results, which were not shown in the previous work.
- arXiv:1908.03794 (replaced) [pdf, other]
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Title: Quantitative Assessment of the Toner and Tu Theory of Polar FlocksComments: All comments welcomeJournal-ref: Phys. Rev. Lett. 123, 218001 (2019)Subjects: Statistical Mechanics (cond-mat.stat-mech); Soft Condensed Matter (cond-mat.soft)
We present a quantitative assessment of the Toner and Tu theory describing the universal scaling of fluctuations in polar phases of dry active matter. Using large scale simulations of the Vicsek model in two and three dimensions, we find the overall phenomenology and generic algebraic scaling predicted by Toner and Tu, but our data on density correlations reveal some qualitative discrepancies. The values of the associated scaling exponents we estimate differ significantly from those conjectured in 1995. In particular, we identify a large crossover scale beyond which flocks are only weakly anisotropic. We discuss the meaning and consequences of these results.
- arXiv:1908.05568 (replaced) [pdf, other]
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Title: Non-stationary Statistics and Formation Jitter in Transient Photon CondensationAuthors: Benjamin T. Walker, João D. Rodrigues, Himadri S. Dhar, Rupert F. Oulton, Florian Mintert, Robert A. NymanJournal-ref: Nat Commun 11, 1390 (2020)Subjects: Statistical Mechanics (cond-mat.stat-mech); Optics (physics.optics); Quantum Physics (quant-ph)
While equilibrium phase transitions are well described by a free-energy landscape, there are few tools to describe general features of their non-equilibrium counterparts. On the other hand, near-equilibrium free-energies are easily accessible but their full geometry is only explored in non-equilibrium, e.g. after a quench. In the particular case of a non-stationary system, however, the concepts of an order parameter and free energy become ill-defined, and a comprehensive understanding of non-stationary (transient) phase transitions is still lacking. Here, we probe transient non-equilibrium dynamics of an optically pumped, dye-filled microcavity which exhibits near-equilibrium Bose-Einstein condensation under steady-state conditions. By rapidly exciting a large number of dye molecules, we quench the system to a far-from-equilibrium state and, close to a critical excitation energy, find delayed condensation, interpreted as a transient equivalent of critical slowing down. We introduce the two-time, non-stationary, second-order correlation function as a powerful experimental tool for probing the statistical properties of the transient relaxation dynamics. In addition to number fluctuations near the critical excitation energy, we show that transient phase transitions exhibit a different form of diverging fluctuations, namely timing jitter in the growth of the order parameter. This jitter is seeded by the randomness associated with spontaneous emission, with its effect being amplified near the critical point. The general character of our results are then discussed based on the geometry of effective free-energy landscapes. We thus identify universal features, such as the formation timing jitter, for a larger set of systems undergoing transient phase transitions. Our results carry immediate implications to diverse systems, including micro- and nano-lasers and growth of colloidal nanoparticles.
- arXiv:1908.07881 (replaced) [pdf]
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Title: Apollonian Packing in Polydisperse EmulsionsComments: 5 pages, 4 figuresJournal-ref: Soft Matter, 2020,16, 2426-2430Subjects: Soft Condensed Matter (cond-mat.soft); Materials Science (cond-mat.mtrl-sci); Chemical Physics (physics.chem-ph)
We have discovered the existence of polydisperse High Internal-Phase-Ratio Emulsions (HIPE) in which the internal-phase droplets, present at 95% volume fraction, remain spherical and organize themselves in the available space according to Apollonian packing rules. These polydisperse HIPE are formed during emulsification of surfactant-poor compositions of oil-surfactant-water two-phase systems. Their droplet size-distributions evolve spontaneously towards power laws with the Apollonian exponent. Small-Angle X-Ray Scattering performed on aged HIPEs demonstrated that the droplet packing structure coincided with that of a numerically simulated Random Apollonian Packing. We argue that these peculiar, space-filling assemblies are a result of coalescence and fragmentation processes obeying simple geometrical rules of conserving total volume and minimizing surface area.
- arXiv:1909.04123 (replaced) [pdf]
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Title: Electrophoretic deposition of WS2 flakes on nanoholes arrays. Role of the used suspension mediumAuthors: Dario Mosconi, Giorgia Giovannini, Nicolo Maccaferri, Michele Serri, Paolo Vavassori, Stefano Agnoli, Denis GaroliJournal-ref: https://www.mdpi.com/1996-1944/12/20/3286Subjects: Materials Science (cond-mat.mtrl-sci); Applied Physics (physics.app-ph)
Here we optimized the electrophoretic deposition process for the fabrication of WS2 plasmonic nanohole integrated structures. We showed how the conditions used for the site selective deposition influenced the properties of the deposited flakes. In particular, we investigated the effect of different suspension medium used during the deposition both in the efficiency of the process and in the stability of WS2 flakes, which were deposited on a ordered arrays of plasmonic nanostructures.
- arXiv:1910.01630 (replaced) [pdf, other]
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Title: Strong planar subsystem symmetry-protected topological phases and their dual fracton ordersComments: 21 pages, 7 figuresJournal-ref: Phys. Rev. Research 2, 012059(R) (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el); Statistical Mechanics (cond-mat.stat-mech); High Energy Physics - Theory (hep-th); Quantum Physics (quant-ph)
We classify subsystem symmetry-protected topological (SSPT) phases in $3+1$D protected by planar subsystem symmetries, which are dual to abelian fracton topological orders. We distinguish between weak SSPTs, which can be constructed by stacking $2+1$D SPTs, and strong SSPTs, which cannot. We identify signatures of strong phases, and show by explicit construction that such phases exist. A classification of strong phases is presented for an arbitrary finite abelian group. Finally, we show that fracton orders realizable via $p$-string condensation are dual to weak SSPTs, while strong SSPTs do not admit such a realization.
- arXiv:1910.06413 (replaced) [pdf, ps, other]
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Title: Nodeless superconducting gap in the candidate topological superconductor Sn$_{1-x}$In$_x$Te for x = 0.7Comments: 5 pages, 6 figuresSubjects: Superconductivity (cond-mat.supr-con)
High-pressure synthesis techniques have allowed for the growth of Sn$_{1-x}$In$_x$Te samples beyond the ambient In-saturation limit of $x$ = 0.5 (T$_c \sim$ 4.5 K). In this study, we present measurements of the temperature dependence of the London penetration depth $\Delta\lambda(T)$ in this superconducting doped topological insulator for $x$ = 0.7, where T$_{c,onset}\approx 5$ K. The results indicate fully gapped BCS-like behavior, ruling out odd-parity $A_{2u}$ pairing; however, odd-parity $A_{1u}$ pairing is still possible. Critical field values measured below 1 K and other superconducting parameters are also presented.
- arXiv:1910.08603 (replaced) [pdf, other]
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Title: Magnetic field control of topological magnon-polaron bands in two-dimensional ferromagnetsJournal-ref: Phys. Rev. B 101, 125111 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We theoretically study magnon-phonon hybrid excitations in a square lattice ferromagnet subjected to a magnetic field by varying the field direction. The bulk bands of hybrid excitations, which are referred to as magnon-polarons, are investigated by considering all three phonon modes: vertical phonon, transverse phonon, and longitudinal phonon. We show that the topological proprieties of three hybridizations are different in terms of the Berry curvature and the Chern numbers. We also find that the topological properties of the bands can be controlled by changing the direction of the magnetic field, exhibiting one or more topological phase transitions. The dependence of thermal Hall conductivity as a function of magnetic field direction is proposed as an experiment probe of our theoretical results.
- arXiv:1910.09481 (replaced) [pdf, ps, other]
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Title: Generation of exchange magnons in thin ferromagnetic films by ultrashort acoustic pulsesAuthors: V.Besse, A.V. Golov, V.S. Vlasov, A. Alekhin, D. Kuzmin, I.V. Bychkov, L.N. Kotov, V.V. TemnovJournal-ref: J. Mag. Mag. Mat. 520, 166320 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci); Other Condensed Matter (cond-mat.other); Strongly Correlated Electrons (cond-mat.str-el)
We investigate generation of exchange magnons by ultrashort, picosecond acoustic pulses propagating through ferromagnetic thin films. Using the Landau-Lifshitz-Gilbert equations we derive the dispersion relation for exchange magnons for an external magnetic field tilted with respect to the film normal. Decomposing the solution in a series of standing spin wave modes, we derive a system of ordinary differential equations and driven harmonic oscillator equations describing the dynamics of individual magnon mode. The external magnetoelastic driving force is given by the time-dependent spatial Fourier components of acoustic strain pulses inside the layer. Dependencies of the magnon excitation efficiencies on the duration of the acoustic pulses and the external magnetic field highlight the role of acoustic bandwidth and phonon-magnon phase matching. Our simulations for ferromagnetic nickel evidence the possibility of ultrafast magneto-acoustic excitation of exchange magnons within the bandwidth of acoustic pulses in thin samples under conditions readily obtained in femtosecond pump-probe experiments.
- arXiv:1910.13383 (replaced) [pdf, other]
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Title: XFe4Ge2 (X = Y, Lu) and Mn3Pt: Filling-enforced magnetic topological metalsJournal-ref: Phys. Rev. B 101, 115122 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci)
Magnetism, coupled with nontrivial band topology, can bring about many interesting and exotic phenomena, so that magnetic topological materials have attracted persistent research interest. However, compared with non-magnetic topological materials (TMs), the magnetic TMs are less studied, since their magnetic structures and topological phase transitions are usually complex and the first-principles predictions are usually sensitive on the effect of Coulomb interaction. In this work, we present a comprehensive investigation of XFe4Ge2 (X = Y, Lu) and Mn3Pt, and find these materials to be filling-enforced magnetic topological metals. Our first-principles calculations show that XFe4Ge2 (X = Y, Lu) host Dirac points near the Fermi level at high symmetry point S. These Dirac points are protected by PT symmetry (P and T are inversion and time-reversal transformations, respectively) and a 2-fold screw rotation symmetry. Moreover, through breaking PT symmetry, the Dirac points would split into Weyl nodes. Mn3Pt is found to host 4-fold degenerate band crossings in the whole high symmetry path of A-Z. We also utilize the GGA+U scheme to take into account the effect of Coulomb repulsion and find that the filling-enforced topological properties are naturally insensitive on U.
- arXiv:1911.00973 (replaced) [pdf]
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Title: Curie Temperature of Emerging Two-Dimensional Magnetic StructuresComments: 2 tables and 6 figuresJournal-ref: Phys. Rev. B 100, 205409 (2019)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci); Statistical Mechanics (cond-mat.stat-mech); Computational Physics (physics.comp-ph)
Recent realizations of intrinsic, long-range magnetic orders in two-dimensional (2D) van der Waals materials have ignited tremendous research interests. In this work, we employ the XXZ Heisenberg model and Monte Carlo simulations to study a fundamental property of these emerging 2D magnetic materials, the Curie temperature (Tc). By including both onsite and neighbor couplings extracted from first-principles simulations, we have calculated Tc of monolayer chromium trihalides and Cr2Ge2Te6, which are of broad interests currently, and the simulation results agree with available measurements. We also clarify the roles played by anisotropic and isotropic interactions in deciding Tc of magnetic orders. Particularly, we find a universal, linear dependence between Tc and magnetic interactions within the parameter space of realistic materials. With this linear dependence, we can predict Tc of general 2D lattice structures, omitting the Monte Carlo simulations. Compared with the widely used Ising model, mean-field theory, and spin-wave theory, this work provides a convenient and quantitative estimation of Tc, giving hope to speeding up the search for novel 2D materials with higher Curie temperatures.
- arXiv:1911.03382 (replaced) [pdf, ps, other]
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Title: On thermal Nieh-Yan anomaly in topological Weyl materialsComments: 4 pages, submitted to JETP Lett. arXiv admin note: substantial text overlap with arXiv:1909.08936Journal-ref: JETP Lett. 110, 789-792 (2019)Subjects: Strongly Correlated Electrons (cond-mat.str-el); Superconductivity (cond-mat.supr-con); High Energy Physics - Theory (hep-th)
We discuss the possibility of a gravitional Nieh-Yan anomaly of the type $\partial_\mu j^\mu_5 =\gamma T^2{\cal T}^a\wedge {\cal T}_a$ in topological Weyl materials, where $T$ is temperature and ${\cal T}^a$ is the effective or emergent torsion. As distinct from the non-universal parameter $\Lambda$ in the conventional (zero temperature) Nieh-Yan anomaly -- with canonical dimensions of momentum -- the parameter $\gamma$ is dimensionless. This suggests that the dimensionless parameter is fundamental, being determined by the geometry, topology and number of the number of chiral quantum fields without any explicit non-universal UV scales. This conforms with previous results in the literature, as well as spectral flow calculations using torsional magnetic field at finite temperature.
- arXiv:1911.03513 (replaced) [pdf, other]
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Title: Ground state and collective excitations of a dipolar Bose-Einstein condensate in a bubble trapAuthors: Pedro de Castro Diniz, Eduardo Amâncio Barbosa Oliveira, Aristeu Rosendo Pontes Lima, Emanuel Alves de Lima HennJournal-ref: Sci Rep 10, 4831 (2020)Subjects: Quantum Gases (cond-mat.quant-gas)
We consider the ground state and the low-lying excitations of dipolar Bose-Einstein condensates in a bubble trap, i.e., a shell-shaped spherically symmetric confining potential. By means of an appropriate Gaussian ansatz, we determine the ground-state properties in the case where the particles interact by means of both the isotropic and short-range contact and the anisotropic and long-range dipole-dipole potential in the thin-shell limit. Moreover, with the ground state at hand, we employ the sum-rule approach to study the monopole, the two-, the three-dimensional quadrupole as well as the dipole modes. We find situations in which neither the virial nor Kohn's theorem can be applied. On top of that, we demonstrate the existence of anisotropic particle density profiles, which are absent in the case with repulsive contact interaction only. These significant deviations from what one would typically expect are then traced back to both the anisotropic nature of the dipolar interaction and the novel topology introduced by the bubble trap.
- arXiv:1911.05382 (replaced) [pdf, other]
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Title: Self-organized bistability and its possible relevance for brain dynamicsComments: 6 figuresJournal-ref: Phys. Rev. Research 2, 013318 (2020)Subjects: Statistical Mechanics (cond-mat.stat-mech); Adaptation and Self-Organizing Systems (nlin.AO); Neurons and Cognition (q-bio.NC)
Self-organized bistability (SOB) is the counterpart of 'self-organized criticality' (SOC), for systems tuning themselves to the edge of bistability of a discontinuous phase transition, rather than to the critical point of a continuous one. The equations defining the mathematical theory of SOB turn out to bear strong resemblance to a (Landau-Ginzburg) theory recently proposed to analyze the dynamics of the cerebral cortex. This theory describes the neuronal activity of coupled mesoscopic patches of cortex, homeostatically regulated by short-term synaptic plasticity. The theory for cortex dynamics entails, however, some significant differences with respect to SOB, including the lack of a (bulk) conservation law, the absence of a perfect separation of timescales and, the fact that in the former, but not in the second, there is a parameter that controls the overall system state (in blatant contrast with the very idea of self-organization). Here, we scrutinize --by employing a combination of analytical and computational tools-- the analogies and differences between both theories and explore whether in some limit SOB can play an important role to explain the emergence of scale-invariant neuronal avalanches observed empirically in the cortex. We conclude that, actually, in the limit of infinitely slow synaptic-dynamics, the two theories become identical, but the timescales required for the self-organization mechanism to be effective do not seem to be biologically plausible. We discuss the key differences between self-organization mechanisms with/without conservation and with/without infinitely separated timescales. In particular, we introduce the concept of 'self-organized collective oscillations' and scrutinize the implications of our findings in neuroscience, shedding new light into the problems of scale invariance and oscillations in cortical dynamics.
- arXiv:1911.06794 (replaced) [pdf, other]
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Title: Majorana bound states in nanowire-superconductor hybrid systems in periodic magnetic fieldsJournal-ref: Phys. Rev. B 101, 125414 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We study how the shape of a periodic magnetic field affects the presence of Majorana bound states (MBS) in a nanowire-superconductor system. Motivated by the field configurations that can be produced by an array of nanomagnets, we consider spiral fields with an elliptic cross-section and fields with two sinusoidal components. We show that MBS are robust to imperfect helical magnetic fields. In particular, if the amplitude of one component is tuned to the value determined by the superconducting order parameter in the wire, the MBS can exist even if the second component has a much smaller amplitude. We also explore the effect of the chemical potential on the phase diagram. Our analysis is both numerical and analytical, with good agreement between the two methods.
- arXiv:1911.08237 (replaced) [pdf, ps, other]
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Title: Evidence for an FFLO state with segmented vortices in the BCS-BEC-crossover superconductor FeSeAuthors: S. Kasahara, Y. Sato, S. Licciardello, M. Čulo, S. Arsenijević, T. Ottenbros, T. Tominaga, J. Böker, I. Eremin, T. Shibauchi, J.Wosnitza, N. E. Hussey, Y. MatsudaComments: 6 pages, 4 figuresJournal-ref: Phys. Rev. Lett. 124, 107001 (2020)Subjects: Superconductivity (cond-mat.supr-con); Quantum Gases (cond-mat.quant-gas); Strongly Correlated Electrons (cond-mat.str-el)
We present resistivity and thermal-conductivity measurements of superconducting FeSe in intense magnetic fields up to 35 T applied parallel to the $ab$ plane. At low temperatures, the upper critical field $\mu_0 H_{c2}^{ab}$ shows an anomalous upturn, while thermal conductivity exhibits a discontinuous jump at $\mu_0 H^{\ast}\approx 24$ T well below $\mu_0 H_{c2}^{ab}$, indicating a first-order phase transition in the superconducting state. This demonstrates the emergence of a distinct field-induced superconducting phase. Moreover, the broad resistive transition at high temperatures abruptly becomes sharp upon entering the high-field phase, indicating a dramatic change of the magnetic-flux properties. We attribute the high-field phase to the Fulde-Ferrel-Larkin-Ovchinnikov (FFLO) state, where the formation of planar nodes gives rise to a segmentation of the flux-line lattice. We point out that strongly orbital-dependent pairing as well as spin-orbit interactions, the multiband nature, and the extremely small Fermi energy are important for the formation of the FFLO state in FeSe.
- arXiv:1911.11175 (replaced) [pdf, other]
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Title: Exact dynamics in dual-unitary quantum circuitsComments: 17 pages, 8 figures; v2: minor revisionJournal-ref: Phys. Rev. B 101, 094304 (2020)Subjects: Statistical Mechanics (cond-mat.stat-mech); Quantum Physics (quant-ph)
We consider the class of dual-unitary quantum circuits in $1+1$ dimensions and introduce a notion of ``solvable'' matrix product states (MPSs), defined by a specific condition which allows us to tackle their time evolution analytically. We provide a classification of the latter, showing that they include certain MPSs of arbitrary bond dimension, and study analytically different aspects of their dynamics. For these initial states, we show that while any subsystem of size $\ell$ reaches infinite temperature after a time $t\propto \ell$, irrespective of the presence of conserved quantities, the light-cone of two-point correlation functions displays qualitatively different features depending on the ergodicity of the quantum circuit, defined by the behavior of infinite-temperature dynamical correlation functions. Furthermore, we study the entanglement spreading from such solvable initial states, providing a closed formula for the time evolution of the entanglement entropy of a connected block. This generalizes recent results obtained in the context of the self-dual kicked Ising model. By comparison, we also consider a family of non-solvable initial mixed states depending on one real parameter $\beta$, which, as $\beta$ is varied from zero to infinity, interpolate between the infinite temperature density matrix and arbitrary initial pure product states. We study analytically their dynamics for small values of $\beta$, and highlight the differences from the case of solvable MPSs.
- arXiv:1912.01312 (replaced) [pdf]
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Title: Reversible Gas Sensing by Ferroelectric Switch and 2D Molecule Multiferroics in In2Se3 MonolayerJournal-ref: J. Mater. Chem. A, 2020Subjects: Materials Science (cond-mat.mtrl-sci)
Two-dimensional ferroelectrics are important quantum materials which have found novel application in nonvolatile memories, however, the effects of reversible polarization on chemical reactions and interaction with environments are rarely studied despite of its importance. Here, based on the first-principles calculations, we found distinct gas adsorption behaviors on the surfaces of ferroelectric In2Se3 layer and the reversible gas caption and release controlled by ferroelectric switch. We rationalize the novel phenomena to the synergistic effect of the different electrostatic potential and electron transfer induced by band alignments between frontier molecular orbitals of gas and band edge states of substrate. Excitingly, the adsorption of paramagnetic gas molecules such as NO and NO2 can induce surface magnetism, which is also sensitive to ferroelectric polarization direction of In2Se3, indicating the application of In2Se3 as threshold magnetic sensors or switcher. Furthermore, it is suggested two NO molecules prefer to ferromagnetically couple with each other, the Curie temperature is polarization dependent which can reach up to 50K, leading to the long-sought 2D molecule multiferroics. The ferroelectric controllable adsorption behavior and molecule multiferroic feature will find extensive application in gas caption, selective catalytic reduction and spintronic device.
- arXiv:1912.01822 (replaced) [pdf, ps, other]
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Title: Dissipative conductivity of a dirty superconductor with Dynes subgap states under a dc bias current up to the depairing current densityAuthors: Takayuki KuboComments: 9 pages, 8 figuresJournal-ref: Phys. Rev. Research 2, 013302 (2020)Subjects: Superconductivity (cond-mat.supr-con); Accelerator Physics (physics.acc-ph)
We study the dissipative conductivity $\sigma_1$ of a dirty superconductor with a finite Dynes parameter $\Gamma$ under a dc-biased weak time-dependent field. The Usadel equation for the current-carrying state is solved to calculate the pair potential, penetration depth, supercurrent density, and quasiparticle spectrum. It is shown that, while the depairing current density $j_d$ for $\Gamma=0$ is coincident with the Kupriyanov-Lukichev theory, a finite $\Gamma$ decreases the superfluid density, resulting in a reduction of $j_d$. The broadening of the peaks of the quasiparticle density of states induced by a combination of a finite $\Gamma$ and a dc bias can reduce $\sigma_1$ below that for the ideal dirty BCS superconductor with $\Gamma=0$, while subgap states at Fermi level proportional to $\Gamma$ results in a residual conductivity at $T\to 0$. We find the optimum combination of $\Gamma$ and the dc bias to minimize $\sigma_1$ by scanning all $\Gamma$ and all currents up to $j_d$. By using the results, it is possible to improve $j_d$ and reduce electromagnetic dissipation in various superconducting quantum devices.
- arXiv:1912.09568 (replaced) [pdf, other]
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Title: Topological models in rotationally symmetric quasicrystalsComments: 13 pages, 16 figures, published PRBJournal-ref: Phys. Rev. B 101, 115413 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el); Quantum Gases (cond-mat.quant-gas)
We investigate the physics of quasicrystalline models in the presence of a uniform magnetic field, focusing on the presence and construction of topological states. This is done by using the Hofstadter model but with the sites and couplings denoted by the vertex model of the quasicrystal, giving the Hofstadter vertex model. We specifically consider two-dimensional quasicrystals made from tilings of two tiles with incommensurate areas, focusing on the five-fold Penrose and the eight-fold Ammann-Beenker tilings. This introduces two competing scales; the uniform magnetic field and the incommensurate scale of the cells of the tiling. Due to these competing scales the periodicity of the Hofstadter butterfly is destroyed. We observe the presence of topological edge states on the boundary of the system via the Bott index that exhibit two way transport along the edge. For the eight-fold tiling we also observe internal edge-like states with non-zero Bott index, which exhibit two way transport along this internal edge. The presence of these internal edge states is a new characteristic of quasicrystalline models in magnetic fields. We then move on to considering interacting systems. This is challenging, in part because exact diagonalization on a few tens of sites is not expected to be enough to accurately capture the physics of the quasicrystalline system, and in part because it is not clear how to construct topological flatbands having a large number of states. We show that these problems can be circumvented by building the models analytically, and in this way we construct models with Laughlin type fractional quantum Hall ground states.
- arXiv:2001.04450 (replaced) [pdf, other]
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Title: Enhancing transport properties in interconnected systems without altering their structureComments: 20 pages, 7 figures, To appear in Physical Review ResearchJournal-ref: Phys.Rev.Research. 2 (2020) 13-5Subjects: Physics and Society (physics.soc-ph); Disordered Systems and Neural Networks (cond-mat.dis-nn); Statistical Mechanics (cond-mat.stat-mech)
Units of complex systems -- such as neurons in the brain or individuals in societies -- must communicate efficiently to function properly: e.g., allowing electrochemical signals to travel quickly among functionally connected neuronal areas in the human brain, or allowing for fast navigation of humans and goods in complex transportation landscapes. The coexistence of different types of relationships among the units, entailing a multilayer represention in which types are considered as networks encoded by layers, plays an important role in the quality of information exchange among them. While altering the structure of such systems -- e.g., by physically adding (or removing) units, connections or layers -- might be costly, coupling the dynamics of subset(s) of layers in a way that reduces the number of redundant diffusion pathways across the multilayer system, can potentially accelerate the overall information flow. To this aim, we introduce a framework for functional reducibility which allow us to enhance transport phenomena in multilayer systems by coupling layers together with respect to dynamics rather than structure. Mathematically, the optimal configuration is obtained by maximizing the deviation of system's entropy from the limit of free and non-interacting layers. Our results provide a transparent procedure to reduce diffusion time and optimize non-compact search processes in empirical multilayer systems, without the cost of altering the underlying structure.
- arXiv:2001.04594 (replaced) [pdf]
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Title: 2D van der Waals Nanoplatelets with Robust FerromagnetismAuthors: Michael C. De Siena, Sidney E. Creutz, Annie Regan, Paul Malinowski, Qianni Jiang, Kyle T. Kluherz, Guomin Zhu, Zhong Lin, James J. De Yoreo, Xiaodong Xu, Jiun-Haw Chu, Daniel R. GamelinComments: 20 pages, 6 figures, plus supporting information of 7 pages, 5 figures. SubmittedJournal-ref: Nano Lett. 2020, 20, 3, 2100-2106Subjects: Materials Science (cond-mat.mtrl-sci); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We have synthesized unique colloidal nanoplatelets of the ferromagnetic two-dimensional (2D) van der Waals material CrI3 and have characterized these nanoplatelets structurally, magnetically, and by magnetic circular dichroism spectroscopy. The isolated CrI3 nanoplatelets have lateral dimensions of ~25 nm and ensemble thicknesses of only ~4 nm, corresponding to just a few CrI3 monolayers. Magnetic and magneto-optical measurements demonstrate robust 2D ferromagnetic ordering in these nanoplatelets with Curie temperatures similar to those observed in bulk CrI3, despite the strong spatial confinement. These data also show magnetization steps akin to those observed in micron-sized few-layer 2D sheets and associated with concerted spin-reversal of individual CrI3 layers within few-layer van der Waals stacks. Similar data have also been obtained for CrBr3 and anion-alloyed Cr(I1-xBrx)3 nanoplatelets. These results represent the first example of laterally confined 2D van der Waals ferromagnets of any composition. The demonstration of robust ferromagnetism at nanometer lateral dimensions opens new doors for miniaturization in spintronics devices based on van der Waals ferromagnets.
- arXiv:2002.01069 (replaced) [pdf, other]
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Title: Nonequilibrium physics in integrable systems and spin-flip non-invariant conserved quantitiesAuthors: Chihiro MatsuiComments: 19 pages, 1 figureJournal-ref: Journal of Physics A: Mathematical and Theoretical, Volume 53 Number 13 (2020), Special Issue PaperSubjects: Statistical Mechanics (cond-mat.stat-mech); Mathematical Physics (math-ph)
Recently found spin-flip non-invariant (SFNI) conserved quantities play important roles in discussing nonequilibrium physics of the XXZ model. The representative examples are the generalized Gibbs ensemble (GGE) and the ballistic transport of the spin current. In spite of big progress in understanding nonequilibrium physics of integrable systems, the general framework to determine a minimal complete set of conserved quantities which describes the long-time steady state has not yet been found. This paper shows that the GGE of the gapless XXZ model consists of functionally independent conserved quantities rather than linearly independent. At the same time, the physical meaning of SFNI conserved quantities is provided. We also discuss that there exist ballistic channels of the spin current supported by non-quasilocal conserved quantities. The saturation of the lower bound for the Drude weight by quasilocal conserved quantities reads the linear dependence of non-quasilocal conserved quantities on quasilocal ones. We show that their (generalized) linearly dependence relation is consistent with the statement that the GGE consists of functionally independent conserved quantities without containing all linearly independent conserved quantities.
- arXiv:2003.02564 (replaced) [pdf, other]
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Title: Realization and transport investigation of a single layer-twisted bilayer graphene junctionComments: 20 pages, 4 figuresJournal-ref: Carbon 163, 105-112 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We report on low-temperature transport study of a single layer graphene (SLG)-twisted bilayer graphene (tBLG) junction device. The SLG-tBLG junction in the device is grown by chemical vapor deposition and the device is fabricated in a Hall-bar configuration on Si/SiO$_2$ substrate. The longitudinal resistances across the SLG-tBLG junction (cross-junction resistances) on the two sides of the Hall bar and the Hall resistances of SLG and tBLG in the device are measured. In the quantum Hall regime, the measurements show that the measured cross-junction resistances exhibit a series of new quantized plateaus and the appearance of these resistance plateaus can be attributed to the presence of the well-defined edge-channel transport along the SLG-tBLG junction interface. The measurements also show that the difference between the cross-junction resistances measured on the two sides of the Hall-bar provides a sensitive measure to the edge channel transport characteristics in the two graphene layers that constitute the SLG-tBLG junction and to degeneracy lifting of the Landau levels in the tBLG layer. Temperature dependent measurements of the cross-junction resistance in the quantum Hall regime are also carried out and the influence of the transverse transport of the bulk Landau levels on the edge channel transport along the SLG-tBLG junction interface are extracted. These results enrich the understanding of the charge transport across interfaces in graphene hybrid structures and open up new opportunities for probing exotic quantum phenomena in graphene devices.
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- arXiv:2003.07374 [pdf, other]
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Title: Quantum Computing for Quantum TunnellingComments: 6 pages, 4 figuresSubjects: High Energy Physics - Phenomenology (hep-ph); Statistical Mechanics (cond-mat.stat-mech); High Energy Physics - Theory (hep-th); Quantum Physics (quant-ph)
We demonstrate how quantum field theory problems can be embedded on quantum annealers. The general method we use is a discretisation of the field theory problem into a general Ising model, with the continuous field values being encoded into Ising spin chains. To illustrate the method, and as a simple proof of principle, we use a (hybrid) quantum annealer to recover the correct profile of the thin-wall tunnelling solution. This method is applicable to many nonperturbative problems.
- arXiv:2003.07376 [pdf, other]
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Title: Tunable two-dimensional superlattices in grapheneAuthors: Robin Huber, Ming-Hao Liu, Szu-Chao Chen, Martin Drienovsky, Andreas Sandner, Kenji Watanabe, Takashi Taniguchi, Klaus Richter, Dieter Weiss, Jonathan EromsComments: 8 pages, 4 figures plus Supplementary Information. Supplementary Movie can be obtained from the authors upon requestSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Electrons in an artificially created periodic potential---a superlattice---follow Bloch's theorem, and they reside in minibands. This approach is particularly suitable to study effects inaccessible in natural crystals, such as Hofstadter's butterfly. After pioneering experiments using high-mobility GaAs based superlattices, additional proof came with graphene-hexagonal boron nitride (hBN) heterostructures forming moir\'{e} superlattices. However, both lattice symmetry and period are constrained by the crystal lattices of graphene and hBN, and the exact potential is governed by, e.g., strain or local band-gaps, which are virtually impossible to be controlled experimentally. A first approach to circumvent this was recently presented by Forsythe et al., who employed a patterned dielectric, and demonstrated gate-tunable superlattice effects. In this work, combining patterned and uniform gates, we demonstrate satellite resistance peaks corresponding to Dirac cones to fourth order, and the Hofstadter butterfly, including the non-monotonic quantum Hall response predicted by Thouless et al. The exact potential shape can be determined from elementary electrostatics, allowing for a detailed comparison between miniband structure and calculated transport characteristics. We thus present a comprehensive picture of graphene-based superlattices, featuring a broad range of miniband effects, both in experiment and in our theoretical modeling.
- arXiv:2003.07378 [pdf, other]
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Title: Ramsey interferometry of non-Hermitian quantum impuritiesComments: 5+5 pages; 2 figuresSubjects: Quantum Gases (cond-mat.quant-gas); Quantum Physics (quant-ph)
We introduce a Ramsey pulse scheme which extracts the non-Hermitian Hamiltonian associated to an arbitrary Lindblad dynamics. We propose a realted protocol to measure via interferometry a generalised Loschmidt echo of a generic state evolving in time with the non-Hermitian Hamiltonian itself, and we apply the scheme to a one-dimensional weakly interacting Bose gas coupled to a stochastic atomic impurity. The Loschmidt echo is mapped into a functional integral from which we calculate the long-time decohering dynamics at arbitrary impurity strengths. For strong dissipation we uncover the phenomenology of a quantum many-body Zeno effect: corrections to the decoherence exponent resulting from the impurity self-energy becomes purely imaginary, in contrast to the regime of small dissipation where they instead enhance the decay of quantum coherences. Our results illustrate the prospects for experiments employing Ramsey interferometry to study dissipative quantum impurities in condensed matter and cold atoms systems.
- arXiv:2003.07381 [pdf, other]
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Title: Chaos in the QFT $S$-matrixAuthors: Vladimir RosenhausComments: 10 pages, 4 figuresSubjects: High Energy Physics - Theory (hep-th); Strongly Correlated Electrons (cond-mat.str-el); Chaotic Dynamics (nlin.CD)
A number of studies have shown that chaos occurs in scattering: the outgoing deflection angle is seen to be an erratic function of the impact parameter. We propose to extend this to quantum field theory, and to use the $S$-matrix as a probe of chaos.
- arXiv:2003.07399 [pdf, other]
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Title: Unsupervised machine learning of quantum phase transitions using diffusion mapsSubjects: Quantum Physics (quant-ph); Statistical Mechanics (cond-mat.stat-mech); Machine Learning (stat.ML)
Experimental quantum simulators have become large and complex enough that discovering new physics from the huge amount of measurement data can be quite challenging, especially when little theoretical understanding of the simulated model is available. Unsupervised machine learning methods are particularly promising in overcoming this challenge. For the specific task of learning quantum phase transitions, unsupervised machine learning methods have primarily been developed for phase transitions characterized by simple order parameters, typically linear in the measured observables. However, such methods often fail for more complicated phase transitions, such as those involving incommensurate phases, valence-bond solids, topological order, and many-body localization. We show that the diffusion map method, which performs nonlinear dimensionality reduction and spectral clustering of the measurement data, has significant potential for learning such complex phase transitions unsupervised. This method works for measurements of local observables in a single basis and is thus readily applicable to many experimental quantum simulators as a versatile tool for learning various quantum phases and phase transitions.
- arXiv:2003.07400 [pdf, ps, other]
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Title: Impressive Electronic Transport in Be$_2$C Monolayer Limited by PhononComments: 19 pages, 7 figuresSubjects: Materials Science (cond-mat.mtrl-sci)
We present thermoelectric properties of Be$_2$C monolayer based on density functional theory combined with semi-classical Boltzmann transport theory. First principles calculations show the material is direct band gap semiconductor with band gap of 2.0 eV obtained with Gaussian-attenuating Perdew-Burke-Ernzerhof (Gau-PBE) hybrid functionals. Kohn-Sham eigen-states obtained with Gau-PBE are fed into Boltzmann transport equation which is solved under constant relaxation time approximation resulting into thermoelectric (TE) coefficient in terms of the relaxation time ($\tau$). In this work, we have explicitly determined the relaxation time by studying the electron-phonon interactions from first principles using Wannier functions to obtain the absolute TE coefficients for the Be$_2$C monolayer along the armchair and zigzag directions. Our results show that the Be$_2$C monolayer has high TE coefficients like Seebeck coefficient ($\alpha$) and electrical conductivity ($\sigma$) leading to high power factor ($\alpha^2\sigma$ $\sim$ 3.44 mW/mK$^2$) along the zigzag direction with p-type doping which is of the similar order observed for the commercial TE materials like doped-Bi$_2$Te$_3$ (J. Appl. Phys. 2003 (93) 368-374; J. Appl. Phys. 2008 (104) 053713-1-053713-5). Further, third-order anharmonic theory yields the slightly high lattice thermal conductivity ($\sim$ 66 W/mK) at 300 K giving rise to moderate figure of merit (ZT $\sim$ 0.1) optimized with p-type doping along the zigzag direction. Our results suggest that Be$_2$C monolayer is promising material for thermoelectric applications as far as high power factor is concerned. Additionally, the dynamical stability of the Be$_2$C monolayer up to 14 \% bi-axial strain shows that phonon tranport in the Be$_2$C monolayer can be further improved through strain engineering.
- arXiv:2003.07412 [pdf, other]
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Title: Drop Impact on Hot Plates: Contact times, Lift-off and the Lamella RuptureAuthors: Sang-Hyeon Lee, Kirsten Harth, Maaike Rump, Minwoo Kim, Detlef Lohse, Kamel Fezzaa, Jung Ho JeComments: S. H. Lee and K. Harth contributed equally to this workSubjects: Fluid Dynamics (physics.flu-dyn); Soft Condensed Matter (cond-mat.soft)
When a liquid drop impacts on a heated substrate, it can remain deposited, or violently boil in contact, or lift off with or without ever touching the surface. The latter is known as the Leidenfrost effect. The duration and area of the liquid--substrate contact is highly relevant for the heat transfer, as well as other effects such as corrosion. However, most experimental studies rely on side view imaging to determine contact times, and those are often mixed with the time until the drop lifts off from the substrate. Here, we develop and validate a reliable method of contact time determination using high-speed X-ray and Total Internal Reflection measurements. We exemplarily compare contact and lift-off times on flat silicon and sapphire substrates. We show that drops can rebound even without formation of a complete vapor layer, with a wide range of lift-off times. On sapphire, we find a local minimum of lift-off times much shorter than by capillary rebound in the comparatively low-temperature regime of transition boiling / thermal atomization. We elucidate the underlying mechanism related to spontaneous rupture of the lamella and receding of the contact area.
- arXiv:2003.07419 [pdf, other]
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Title: Polynomial scaling of QAOA for ground-state preparation: taming first-order phase transitionsComments: 4 pages, 4 figures, Appendices 5 pagesSubjects: Quantum Physics (quant-ph); Statistical Mechanics (cond-mat.stat-mech)
We show that the quantum approximate optimization algorithm (QAOA) can construct with polynomially scaling resources the ground state of the fully-connected p-spin Ising ferromagnet, a problem that notoriously poses severe difficulties to a Quantum Annealing (QA) approach, due to the exponentially small gaps encountered at first-order phase transition for ${\rm p} \ge 3$. For a generic target state, we find that an appropriate QAOA parameter initialization is necessary to achieve a good performance of the algorithm when the number of variational parameters $2{\rm P}$ is much smaller that the system size ${\rm N}$, because of the large number of sub-optimal local minima. We find that when ${\rm P} > {\rm P}^*_{\rm N} \propto {\rm N}$, the structure of the parameter space simplifies, as all minima become degenerate. This allows to achieve the ground state with perfect fidelity with a number of parameters scaling extensively with ${\rm N}$, and with resources scaling polynomially with ${\rm N}$.
- arXiv:2003.07420 [pdf, ps, other]
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Title: A cryogenic-helium pipe flow facility with unique double-line molecular tagging velocimetry capabilityComments: 9 pages, 11 figuresSubjects: Other Condensed Matter (cond-mat.other); Fluid Dynamics (physics.flu-dyn); Instrumentation and Detectors (physics.ins-det)
Cryogenic helium-4 has extremely small kinetic viscosity, which makes it a promising material for high Reynolds ($Re$) number turbulence research in compact laboratory apparatuses. In its superfluid phase (He II), helium has an extraordinary heat transfer capability and has been utilized in various scientific and engineering applications. In order to unlock the full potential of helium in turbulence research and to improve our understanding of the heat transfer mechanism in He II, a flow facility that allows quantitative study of helium heat-and-mass transfer processes is needed. Here we report our work in assembling and testing a unique helium pipe flow facility that incorporates a novel double-line molecular tracking velocimetry (DL-MTV) system. This flow facility allows us to generate turbulent pipe flows with $Re$ above $10^7$, and it can also be adapted to produce heat-induced counterflow in He II. The DL-MTV system, which is based on the generation and tracking of two parallel thin He$^*_2$ molecular tracer lines with an adjustable separation distance, allows us to measure not only the velocity profile but also both the transverse and longitudinal spatial velocity structure functions. We have also installed a deferential pressure sensor to the flow pipe for pressure drop measurement. The testing results of the flow facility and the measurement devices are presented. We discuss how this facility will allow us to solve some outstanding problems in the helium heat-and-mass transfer topic area.
- arXiv:2003.07430 [pdf, other]
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Title: Spin to pseudo-spin conversion in graphene-like systems: A Kubo formalism including vertex correctionsSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Other Condensed Matter (cond-mat.other)
Spin to pseudo-spin conversion by which spin population imbalance converts to non-equilibrium pseudo-spin density in Dirac systems has been investigated particularly for graphene and insulator phase of silicene. Calculations have been performed within the Kubo approach and by taking into account the vertex correction. Results indicate that spin converts to pseudo-spin in either graphene or silicene that identified to come from the spin-orbit interactions. The response function of spin to pseudo-spin conversion is weakened several orders of magnitude by vertex correction of impurities in graphene, however, this conversion is strengthened in insulator silicene. In addition, in the case of silicene, results are indicative of an obvious change in the mentioned response function as a result of the change in band-topology which can be observed by manipulation of external electric field, vertically applied to the system surface. At the critical electric field in which the topological phase transition for silicene nano-ribbon has been observed, response function changes abruptly. Interconversion between the quantum numbers could provide a field for information and data processing technologies.
- arXiv:2003.07437 [pdf, other]
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Title: Inverse Faraday effect in graphene and Weyl semimetalsAuthors: I.D.Tokman, Qianfan Chen, I.A. Shereshevsky, V.I.Pozdnyakova, Ivan Oladyshkin, Mikhail Tokman, Alexey BelyaninComments: 28 pages, 5 figuresJournal-ref: Phys. Rev. B 101, 174429 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Quantum Physics (quant-ph)
We report systematic theoretical studies of the inverse Faraday effect in materials with massless Dirac fermions, both in two dimensions such as graphene and surface states in topological insulators, and in three dimensions such as Dirac and Weyl semimetals. Both semiclassical and quantum theories are presented, with dissipation and finite size effects included. We find that the magnitude of the effect can be much stronger in Dirac materials as compared to conventional semiconductors. Analytic expressions for the optically induced magnetization in the low temperature limit are obtained. Strong inverse Faraday effect in Dirac materials can be used for the optical control of magnetization, all-optical modulation, and optical isolation.
- arXiv:2003.07451 [pdf, other]
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Title: Physical Resurgent ExtrapolationComments: 11 pages, 8 figuresSubjects: High Energy Physics - Theory (hep-th); Other Condensed Matter (cond-mat.other); Mathematical Physics (math-ph)
Expansions of physical functions are controlled by their singularities, which have special structure because they themselves are physical, corresponding to instantons, caustics or saddle configurations. Resurgent asymptotics formalizes this idea mathematically, and leads to significantly more powerful extrapolation methods to extract physical information from a finite number of terms of an expansion, including precise decoding of non-perturbative effects.
- arXiv:2003.07458 [pdf, ps, other]
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Title: Dimensional crossovers and Casimir forces for the Bose gas in anisotropic optical latticesComments: 12 pages, 5 figures, Text changes in the section IIISubjects: Statistical Mechanics (cond-mat.stat-mech); Quantum Gases (cond-mat.quant-gas)
We consider the Bose gas on a $d$-dimensional anisotropic lattice employing the imperfect (mean-field) gas as a prototype example. We study the dimensional crossover arising as a result of varying the dispersion relation at finite temperature $T$. We analyze in particular situations where one of the relevant effective dimensionalities is located at or below the lower critical dimension, so that the Bose-Einstein condensate becomes expelled from the system by anisotropically modifying the lattice parameters controlling the kinetic term in the Hamiltonian. We clarify the mechanism governing this phenomenon. Subsequently we study the thermodynamic Casimir effect occurring in this system. We compute the exact profile of the scaling function for the Casimir energy. As an effect of strongly anisotropic scale invariance, the Casimir force below or at the critical temperature $T_c$ may be repulsive even for periodic boundary conditions. The corresponding Casimir amplitude is universal only in a restricted sense, and the power law governing the decay of the Casimir interaction becomes modified. We also demonstrate that, under certain circumstances, the scaling function is constant for suffciently large values of the scaling variable, and in consequence is not an analytical function. At $T > T_c$ the Casimir-like interactions reflect the structure of the correlation function, and, for certain orientations of the confining walls, show exponentially damped oscillatory behavior so that the corresponding force is attractive or repulsive depending on the distance.
- arXiv:2003.07462 [pdf, other]
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Title: The Structure of Molten FLiNaKAuthors: Benjamin A. Frandsen, Stella D. Nickerson, Austin D. Clark, Andrew Solano, Raju Baral, Johnny Williams, Jörg Neuefeind, Matthew MemmottJournal-ref: Journal of Nuclear Materials 537 (2020) 152219Subjects: Materials Science (cond-mat.mtrl-sci)
The structure of the molten salt (LiF)$_{0.465}$(NaF)$_{0.115}$(KF)$_{0.42}$ (FLiNaK), a potential coolant for molten salt nuclear reactors, has been studied by ab initio molecular dynamics simulations and neutron total scattering experiments. We find that the salt retains well-defined short-range structural correlations out to approximately 9 Angstroms at typical reactor operating temperatures. The experimentally determined pair distribution function can be described with quantitative accuracy by the molecular dynamics simulations. These results indicate that the essential ionic interactions are properly captured by the simulations, providing a launching point for future studies of FLiNaK and other molten salts for nuclear reactor applications.
- arXiv:2003.07466 [pdf]
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Title: Shapes of rotating normal fluid 3He versus superfluid 4He droplets in molecular beamsAuthors: Deepak Verma, Sean M. O. O Connell, Alexandra J. Feinberg, Swetha Erukala, Rico M. Tanyag, Charles Bernando, Weiwu Pang, Catherine A. Saladrigas, Benjamin W. Toulson, Mario Borgwardt, Niranjan Shivaram, Ming-Fu Lin, Andre Al Haddad, Wolfgang Jäger, Christoph Bostedt, Peter Walter, Oliver Gessner, Andrey F. VilesovComments: 29 pages, 6 figuresSubjects: Other Condensed Matter (cond-mat.other); Soft Condensed Matter (cond-mat.soft); Atomic and Molecular Clusters (physics.atm-clus)
Previous single-pulse extreme ultraviolet and X-ray coherent diffraction studies revealed that superfluid 4He droplets obtained in free jet expansion acquire sizable angular momentum, resulting in significant centrifugal distortion. Similar experiments with normal fluid 3He droplets may help elucidating the origin of the of the large degree of rotational excitation and highlight similarities and differences of dynamics in normal and superfluid droplets. Here, we present the first comparison of the shapes of isolated 3He and 4He droplets following expansion of the corresponding fluids in vacuum at temperatures as low as ~ 2 K. Large 3He and 4He droplets with average radii of ~160 nm and ~350 nm, respectively, were produced. We find that the majority of the 3He droplets in the beam correspond to rotating oblate spheroids with reduced average angular momentum ($\Lambda$) and reduced angular velocities ($\Omega$) similar to that of 4He droplets. Given the different physical nature of 3He and 4He, this similarity in $\Lambda$ and $\Omega$ may be surprising and suggest that similar mechanisms induce rotation regardless of the isotope. We hypothesized that the observed distribution of droplet sizes and angular momenta stem from processes in the dense region close to the nozzle. In this region, the significant velocity spread and collisions between the droplets induce excessive rotation followed by droplet fission. The process may repeat itself several times before the droplets enter the collision-fee high vacuum region further downstream.
- arXiv:2003.07470 [pdf]
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Title: An Experimental and Computational Study on Material Dispersion of 1-Alkyl-3-Methylimidazolium Tetrafluoroborate Ionic LiquidsAuthors: Carlos Damián Rodríguez Fernández (1), Yago Arosa (1), Bilal Algnamat (1 and 2), Elena López Lago (1), Raúl de la Fuente (1) ((1) Universidade de Santiago de Compostela (2) Al-Hussein Bin Talal University)Comments: 34 pages, 12 figuresSubjects: Soft Condensed Matter (cond-mat.soft)
The material dispersion of the [Ckmim][BF4] (k = 2,3,4,6,7,8,10) family of ionic liquids is measured at several temperatures over a broad spectral range from 300 nm to 1550 nm. The experimental curves are fitted to a modified three-resonance Sellmeier model to understand the effect of temperature and alkyl chain length in the dispersion. From the parameters of the fitting, we analyze the influence that the different constituents of these ionic liquids have in the dispersion behaviour. In addition, a semi-empirical approach combining simulated electronic polarizabilities and experimental densities for predicting the material dispersion is successfully tested by direct comparison with the experimental results. The limitations of this method are analyzed in terms of the structure of the ionic liquids. The results of this work aim to increase our knowledge about how the structure of an ionic liquid influences its material dispersion. Understanding this influence is fundamental to produce ionic liquids with tailored optical properties.
- arXiv:2003.07479 [pdf, other]
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Title: Number Parity effect in the normal state of $SrTiO_3$Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Superconductivity (cond-mat.supr-con)
We study the recently discovered even-odd effects in the normal state of single-electron devices manufactured at strontium titanium oxide/lanthanum aluminum oxide interfaces (STO/LAO). Within the framework of the number parity-projected formalism and a phenomenological fermion-boson model we find that, in sharp contrast to conventional superconductors, the crossover temperature $T^*$ for the onset of number parity effect is considerably larger than the superconducting transition temperature $T_c$ due to the existence of a pairing gap above $T_c$. Furthermore, the finite lifetime of the preformed pairs reduces by several orders of magnitude the effective number of states $N_{\rm eff}$ available for the unpaired quasiparticle in the odd parity state of the Coulomb blockaded STO/LAO island. Our findings are in qualitative agreement with the experimental results reported by Levy and coworkers for STO/LAO based single electron devices.
- arXiv:2003.07485 [pdf]
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Title: Active control of near-field radiative heat transfer by coating-twisting methodComments: 4pages,6 figuresSubjects: Applied Physics (physics.app-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
In this letter, active control of near-field radiative heat transfer (NFRHT) between two isotropic materials is realized by a coating-twisting method. The two slabs are coated with graphene gratings, and then the NFRHT can be not only enhanced, but also weakened, by tuning the twisted angle between the two gratings. The physical mechanism is attributed to the modes coupled by the graphene gratings and the isotropic material, which can vary with the twisted angle. The proposed method is also applicable for other kinds of anisotropic films, and may provide a way to realize high-precision nanoscale thermal management, nimble thermal communications and thermal switch.
- arXiv:2003.07518 [pdf, ps, other]
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Title: A possible mechanism of the lifetime effects of electron pairs at the $SrTiO_3/LaTiO_3$ interfaceAuthors: Xing YangSubjects: Superconductivity (cond-mat.supr-con); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
The lifetime effects of the electron pairs are supposed to be responsible for the atypical behavior of the single electron transistors manufactured at the strontium titanate/ lanthanum aluminate (STO/LAO) interface. In addition, as shown in Richter's experiments, the energy gap $\Delta$ should persist above the superconducting transition temperature $T_c$. In order to explain the experiments, the present paper attempts to associate the phonon-electron interactions to the mechanism of the formation and decay of the electron pairs. Moreover, through employing the boson fermion model that includes two superconducting mechanisms, we reproduce the step-like $\Delta-T_c$ relations with the energy gap $\Delta$ remaining finite above $T_c$. The results are roughly consistent with the experiments. The newly-introduced models and formalism may be helpful in describing superconductors with lifetime effects and a finite energy gap $\Delta$ above $T_c$.
- arXiv:2003.07531 [pdf]
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Title: Strong antiferromagnetic interaction owing to a large trigonal distortion in the spin-orbit-coupled honeycomb lattice iridate CdIrO$_3$Comments: 6 pages, 4 figures, accepted for publication in Physical Review MaterialsJournal-ref: Phys. Rev. Materials 4, 044401 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el); Materials Science (cond-mat.mtrl-sci)
We investigated the magnetic properties of the ilmenite-type iridate CdIrO$_3$ with a honeycomb lattice formed by Ir$^{4+}$ ions prepared via a solid-state metathesis. The magnetization measurements with using the powder sample reveal a large effective magnetic moment and a fairly strong antiferromagnetic interaction, indicating a deviation from the Kitaev model. Considering the relationship between magnetism and crystal structure in CdIrO$_3$ with comparing with the other ilmenite-type iridates ZnIrO$_3$ and MgIrO$_3$, we conclude that insulating CdIrO$_3$ cannot be describe as a $J_{\rm eff} = 1/2$ Mott state owing to a metathetically-stabilized large trigonal distortion of IrO$_6$ octahedra.
- arXiv:2003.07533 [pdf, other]
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Title: Spin-transport in superconductorsAuthors: K. Ohnishi, S. Komori, G. Yang, K.-R. Jeon, L. A. B. Olde Olthof, X. Montiel, M. G. Blamire, J. W. A. RobinsonComments: Accepted in APL PerspectivesJournal-ref: Appl. Phys. Lett. 116, 130501 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Superconductivity (cond-mat.supr-con)
Spin-transport in superconductors is a subject of fundamental and technical importance with the potential for applications in superconducting-based cryogenic memory and logic. Research in this area is rapidly intensifying with recent discoveries establishing the field of superconducting spintronics. In this perspective we provide an overview of the experimental state-of-the-art with a particular focus on local and nonlocal spin-transport in superconductors, and propose device schemes to demonstrate the viability of superconducting spin-based devices.
- arXiv:2003.07535 [pdf]
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Title: Functionalized Carbon Nanotube Electrodes for Controlled DNA SequencingSubjects: Applied Physics (physics.app-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
In the last decade, solid state nanopores nanogaps have attracted significant interest in the rapid detection of DNA nucleotides. However, reducing the noise through the controlled translocating of the DNA nucleobases is a central issue for the developing nanogap nanopore based DNA sequencing to achieve single nucleobase resolution. Furthermore, the high reactivity of the graphene pores gaps exhibits clogging of the pore gap, leading to the blockage of the pores gaps, yielding sticking, and irreversible pore closure. To address the prospective of functionalization of carbon nanostructure and for accomplishing this objective, herein, we have studied the performance of functionalized closed end cap carbon nanotube CNT nanogap embedded electrodes which can improve the coupling through nonbonding electrons and may provide the possibility of N and O and H pi interaction with nucleotides, as single stranded DNA is transmigrated across. We have investigated the effect of functionalizing the closed end cap CNT6,6 electrodes with purine adenine, guanine and pyrimidine thymine, cytosine molecules. Weak hydrogen bonds formed between the probe molecule and target DNA nucleobase enhance the electronic coupling and temporarily stabilize the translocating nucleobase against the orientational fluctuations, which may reduce noise in the current signal during experimental measurements. The findings of our density functional theory and non equilibrium Greens function based study indicates that this modeled setup could allow DNA nucleotide sequencing with a better and reliable yield, giving current traces that differ by at least 1 order of current magnitude for all four target nucleotides. Thus, we feel that functionalized CNT nanogap embedded electrodes may be utilized for controlled DNA sequencing.
- arXiv:2003.07546 [pdf]
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Title: The physical and mechanical properties of hafnium orthosilicate: experiments and first-principles calculationsAuthors: Zhidong Ding, Mackenzie Ridley, Jeroen Deijkers, Naiming Liu, Md Shafkat Bin Hoque, John Gaskins, Mona Zebarjadi, Patrick Hopkins, Haydn Wadley, Elizabeth Opila, Keivan EsfarjaniSubjects: Materials Science (cond-mat.mtrl-sci)
Hafnium orthosilicate (HfSiO4: hafnon) has been proposed as an environmental barrier coating (EBC) material to protect silicon coated, silicon-based ceramic materials at high temperatures and as a candidate dielectric material in microelectronic devices. It can naturally form at the interface between silicon dioxide (SiO2) and hafnia (HfO2). When used in these applications, its coefficient of thermal expansion (CTE) should match that of silicon and SiC composites to reduce the stored elastic strain energy, and thus risk of failure of these systems. The physical, mechanical, thermodynamic and thermal transport properties of hafnon have been investigated using a combination of both density functional theory (DFT) calculations and experimental assessments. The average linear coefficient of thermal expansion (CTE) calculated using the quasi-harmonic approximation increase from 3.06 10-6 K-1 to 6.36 10-6 K-1, as the temperature increases from 300 to 1500 K, in agreement with both X-ray diffraction lattice parameter and dilatometry measurements. The predicted thermal conductivity from Boltzmann transport theory was approximately 18 W/m.K at 300K. Both hot disk and laser flash measurements gave a thermal conductivity of 13.3 W/m.K. This slightly lower value is indicative of residual disorder in the experimental samples that was absent in the theoretical analysis. First-principles calculations and nanoindentation techniques were used to assess the ambient temperature elastic constants and bulk modulus respectively. The elastic properties obtained by both approaches agreed to within 5% validating the computational approach and its future use for study of the thermomechanical properties of other oxides or silicates.
- arXiv:2003.07547 [pdf, ps, other]
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Title: Dynamics of a viscoelastic liquid filament connected to two mobile dropletsComments: 19 pages, 5 figures, submitted to Phys. FluidsSubjects: Soft Condensed Matter (cond-mat.soft); Fluid Dynamics (physics.flu-dyn)
A filament of liquid is usually unstable and breaks up into small droplets, while a filament of polymer solution is known to be quite stable against such instability, and they form a stable configuration of filament connecting two spherical droplets. If the droplets are fixed in space, the liquid flows from the filament region to the droplet region to reduce the surface energy and the filament gets thinner. If the whole liquid is placed in another viscous fluid, the droplets approach each other, and the filament can get thicker. Here we study the dynamics of such system. We derive time evolution equations for the radius and the length of the filament taking into account the fluid flux from filament to droplets and the motion of the droplets. We will show that (a) if the centers of the droplets are fixed, the filament thins following the classical prediction of Entov and Hinch, and that (b) if the droplets are mobile (subject to the Stokes drag in the viscous medium), the thinning of the filament is suppressed, and under certain conditions, the filament thickens. This theory explains the phenomena observed by Yang and Xu [Phys. Fluids 20, 043101 (2008)] in four-roller mill device.
- arXiv:2003.07556 [pdf, ps, other]
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Title: Spontaneous spin-loop-current order mediated by transverse spin fluctuations in cuprate superconductorsComments: 10 pages, 11 figuresSubjects: Strongly Correlated Electrons (cond-mat.str-el); Superconductivity (cond-mat.supr-con)
We predict the theoretical occurrence of nanoscale spontaneous spin-current, called the spin loop-current (sLC) order, as a promising origin of the pseudogap and electronic nematicity in cuprates. We demonstrate that the spontaneous sLC is accompanied by the exotic odd-parity electron-hole pairs that are mediated by transverse spin fluctuations around the pseudogap temperature $T^*$. The present theory predicts the occurrence of the condensation of odd-parity magnon pairs simultaneously. The sLC order is ``hidden'' in that neither internal magnetic field nor charge density modulation is induced, whereas the predicted sLC with finite wavenumber naturally gives the Fermi arc structure. In addition, the fluctuations of sLC order work as attractive pairing interaction between adjacent hot spots, which enlarges the $d$-wave superconducting transition temperature $T_c$. Thus, the sLC state will be the key ingredient in understanding pseudogap, electronic nematicity as well as superconductivity in cuprates and other strongly correlated metals.
- arXiv:2003.07567 [pdf]
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Title: Origin of magnetovolume effect in a cobaltiteAuthors: Ping Miao, Zhijian Tan, Sanghyun Lee, Yoshihisa Ishikawa, Shuki Torii, Masao Yonemura, Akihiro Koda, Kazuki Komatsu, Shinichi Machida, Asami Sano-Furukawa, Takanori Hattori, Xiaohuan Lin, Kuo Li, Takashi Mochiku, Ryosuke Kikuchi, Chizuru Kawashima, Hiroki Takahashi, Qingzhen Huang, Shinichi Itoh, Ryosuke Kadono, Yingxia Wang, Feng Pan, Kunihiko Yamauchi, Takashi KamiyamaSubjects: Strongly Correlated Electrons (cond-mat.str-el); Materials Science (cond-mat.mtrl-sci)
The layered perovskite PrBaCo2O5.5+x demonstrates a strong negative thermal expansion (NTE) which holds potential for being fabricated into composites with zero thermal expansion. The NTE was found to be intimately associated with the spontaneous magnetic ordering, known as magnetovolume effect (MVE). Here we report with compelling evidences that the continuous-like MVE in PrBaCo2O5.5+x is intrinsically of discontinuous character, originating from an magnetoelectric transition from an antiferromagnetic insulating large-volume (AFILV) phase to a ferromagnetic metallic small-volume (FMSV) phase. Furthermore, the magnetoelectric effect (ME) shows high sensitivity to multiple external stimuli such as temperature, carrier doping, hydrostatic pressure, magnetic field etc. In contrast to the well-known ME such as colossal magnetoresistance and multiferroic effect which involve symmetry breaking of crystal structure, the ME in the cobaltite is purely isostructural. Our discovery provides a new pathway to realizing the ME as well as the NTE, which may find applications in new techniques.
- arXiv:2003.07585 [pdf, other]
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Title: NMR-based gap behavior related to the quantum size effectAuthors: Tomonori Okuno, Masahiro Manago, Shunsaku Kitagawa, Kenji Ishida, Kohei Kusada, Hiroshi KitagawaComments: 11 pages, 10 figures, including supplemental materials, accepted for publication in Phys. Rev. B as a Rapid CommunicationSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We conducted$^{195}$Pt-nuclear magnetic resonance measurements on various-diameter Pt nanoparticles coated with polyvinylpyrrolidone in order to detect the quantum size effect and the discrete energy levels in the electron density of states, both of which were predicted by Kubo more than 50 years ago. We succeeded in separating the signals arising from the surface and interior regions and found that the nuclear spin-lattice relaxation rates in both regions show the metallic behavior at high temperatures. Surprisingly, the magnetic fluctuations in both regions exhibited anomalous behavior below the same temperature $T^*$, which points to a clear size dependence and is well scaled with $\delta_\mathrm{Kubo}$. These results suggest that a size-tunable metal-insulator transition occurs in the Pt nanoparticles as a result of the Kubo effect.
- arXiv:2003.07586 [pdf]
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Title: A new theory of fluid-solid coupling in a porous medium for application to the ultrasonic evaluation of tissue remodeling using bioelastomersSubjects: Medical Physics (physics.med-ph); Soft Condensed Matter (cond-mat.soft); Tissues and Organs (q-bio.TO)
Bioelastomers have demonstrated tremendous value and potential in the field of tissue repair due to increasing health demands. Improved non-invasive methods are required for monitoring tissue development assisted by bioelastomers. In this paper, we present a novel theory of fluid-solid coupling in a porous medium for application to the ultrasonic evaluation of tissue remodeling using bioelastomers. The common assumption of equal solid and liquid displacements used in the conventional description of a fluid-saturated porous solid cannot be applied to soft media, such as bioelastomers. We revise the geoacoustic theory of Biot to allow for relative motion between a fluid and a solid in an aggregate and derive an expression for a characteristic fluid-solid coupling parameter. Unlike the conventional method, the propagation speed of shear waves observed by ultrasound shear wave elastography is considered a known quantity in the novel theory, and the calculated value of the coupling parameter is used to evaluate the status of tissue repair. The model is validated by analyzing selected cases. The conditions under which the model can be applied are identified. However, further development of the theory is required to extract dynamic parameters that can be used to monitor the entire tissue remodeling process. In this paper, a theoretical approach is developed that can be used to analyze the mechanics of tissue repair. The theory has potential applications in the field of acellular in situ tissue engineering for non-invasive monitoring of the complex mechanical remodeling process of tissue regeneration and bioelastomer degradation.
- arXiv:2003.07590 [pdf, other]
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Title: On the Spectrum of Multi-Space Euclidean Random MatricesJournal-ref: Phys. Rev. E 101, 052133 (2020)Subjects: Disordered Systems and Neural Networks (cond-mat.dis-nn); Statistical Mechanics (cond-mat.stat-mech)
We consider the additive superimposition of an extensive number of independent Euclidean Random Matrices in the high-density regime. The resolvent is computed with techniques from free probability theory, as well as with the replica method of statistical physics of disordered systems. Results for the spectrum and eigenmodes are shown for a few applications relevant to computational neuroscience, and are corroborated by numerical simulations.
- arXiv:2003.07592 [pdf, other]
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Title: Hole-phonon interactions in quantum dots: Effects of phonon confinement and encapsulation materials on spin-orbit qubitsComments: 17 pages, 10 figures + 10 pages supplementary informationSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Spin-phonon interactions are one of the mechanisms limiting the lifetime of spin qubits made in semiconductor quantum dots. At variance with other mechanisms such as charge noise, phonons are intrinsic to the device and can hardly be mitigated. They set, therefore fundamental limits to the relaxation time of the qubits. Here we introduce a general framework for the calculation of the spin (and charge) transition rates induced by bulk (3D) and strongly confined 1D or 2D phonons. We discuss the particular case of hole spin-orbit qubits described by the 6 bands kp model. We next apply this theory to a hole qubit in a silicon-on-insulator device. We show that spin relaxation in this device is dominated by a band mixing term that couples the holes to transverse acoustic phonons through the valence band deformation potential d, and optimize the bias point and magnetic field orientation to maximize the number of Rabi oscillations Q that can be achieved within on relaxation time T1. Despite the strong spin-orbit coupling in the valence band, the phonon-limited Q can reach a few tens of thousands. We next explore the effects of phonon confinement in 1D and 2D structures, and the impact of the encapsulation materials on the relaxation rates. We show that the spin lifetimes can depend on the structure of the device over micrometer-long length scales and that they improve when the materials around the qubit get harder. Phonon engineering in semiconductor qubits may therefore become relevant once the extrinsic sources of relaxation have been reduced.
- arXiv:2003.07597 [pdf, other]
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Title: Non-Bloch band theory of non-Hermitian Hamiltonians in the symplectic classComments: 13 pages, 2 figuresJournal-ref: Phys. Rev. B 101, 195147 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Mathematical Physics (math-ph); Quantum Physics (quant-ph)
Non-Hermitian Hamiltonians are generally sensitive to boundary conditions, and their spectra and wave functions under open boundary conditions are not necessarily predicted by the Bloch band theory for periodic boundary conditions. To elucidate such a non-Bloch feature, recent works have developed a non-Bloch band theory that works even under arbitrary boundary conditions. Here, it is demonstrated that the standard non-Bloch band theory breaks down in the symplectic class, in which non-Hermitian Hamiltonians exhibit Kramers degeneracy because of reciprocity. Instead, a modified non-Bloch band theory for the symplectic class is developed in a general manner, as well as illustrative examples. This nonstandard non-Bloch band theory underlies the $\mathbb{Z}_{2}$ non-Hermitian skin effect protected by reciprocity.
- arXiv:2003.07600 [pdf, other]
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Title: Experimental and theoretical study of electronic and hyperfine properties of hydrogenated anatase (TiO$_2$): defects interplay and thermal stabilityAuthors: D.V. Zyabkin, H.P. Gunnlaugsson, J.N. Goncalves, K. Bharuth-Ram, B. Qi, I. Unzueta, D. Naidoo, R. Mantovan, H. Masenda, S. Olafsson, G. Peters, J. Schell, U. Vetter, A. Dimitrova, S. Krischok, P. SchaafSubjects: Materials Science (cond-mat.mtrl-sci)
In this study we report on the results from emission $^{57}$Fe M${\"o}$ssbauer Spectroscopy experiments, using dilute $^{57}$Mn implantation into pristine (TiO$_2$) and hydrogenated anatase held at temperatures between 300-700 K. Results of the electronic structure and local environment are complemented with ab-initio calculations. Upon implantation both Fe$^{2+}$ and Fe$^{3+}$ are observed in pristine anatase, where the latter demonstrates the spin-lattice relaxation. The spectra obtained for hydrogenated anatase show no Fe$^{3+}$ contribution, suggesting that hydrogen acts as a donor. Due to the low threshold, hydrogen diffuses out of the lattice. Thus showing a dynamic behavior on the time scale of the $^{57}$Fe 14.4 keV state. The surrounding oxygen vacancies favor the high-spin Fe$^{2+}$ state. The sample treated at room temperature shows two distinct processes of hydrogen motion. The motion commences with the interstitial hydrogen, followed by switching to the covalently bound state. Hydrogen out-diffusion is hindered by bulk defects, which could cause both processes to overlap. Supplementary UV-Vis and electrical conductivity measurements show an improved electrical conductivity and higher optical absorption after the hydrogenation. X-ray photoelectron spectroscopy at room temperature reveals that the sample hydrogenated at 573 K shows presence of both Ti$^{3+}$ and Ti$^{2+}$ states. This could imply that a significant amount of oxygen vacancies and -OH bonds are present in the samples. Theory suggests that in the anatase sample implanted with Mn(Fe), probes were located near equatorial vacancies as next-nearest-neighbours, whilst a metastable hydrogen configuration is responsible for the annealing behavior.
- arXiv:2003.07604 [pdf, other]
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Title: Dynamic Kibble-Zurek scaling framework for open dissipative many-body systems crossing quantum transitionsComments: 15 pages, 8 figuresJournal-ref: Phys. Rev. Research 2, 023211 (2020)Subjects: Statistical Mechanics (cond-mat.stat-mech); Quantum Physics (quant-ph)
We study the quantum dynamics of many-body systems, in the presence of dissipation due to the interaction with the environment, under Kibble-Zurek (KZ) protocols in which one Hamiltonian parameter is slowly, and linearly in time, driven across the critical value of a zero-temperature quantum transition. In particular we address whether, and under which conditions, open quantum systems can develop a universal dynamic scaling regime similar to that emerging in closed systems. We focus on a class of dissipative mechanisms whose dynamics can be reliably described through a Lindblad master equation governing the time evolution of the system's density matrix. We argue that a dynamic scaling limit exists even in the presence of dissipation, whose main features are controlled by the universality class of the quantum transition. This requires a particular tuning of the dissipative interactions, whose decay rate $u$ should scale as $u\sim t_s^{-\kappa}$ with increasing the time scale $t_s$ of the KZ protocol, where the exponent $\kappa = z/(y_\mu+z)$ depends on the dynamic exponent $z$ and the renormalization-group dimension $y_\mu$ of the driving Hamiltonian parameter. Our dynamic scaling arguments are supported by numerical results for KZ protocols applied to a one-dimensional fermionic wire undergoing a quantum transition in the same universality class of the quantum Ising chain, in the presence of dissipative mechanisms which include local pumping, decay, and dephasing.
- arXiv:2003.07607 [pdf, other]
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Title: Tuning the rheological behavior of colloidal gels through competing interactionsJournal-ref: Phys. Rev. Materials 4, 045601 (2020)Subjects: Soft Condensed Matter (cond-mat.soft)
We study colloidal gels formed by competing electrostatic repulsion and short-range attraction by means of extensive numerical simulations under external shear. We show that, upon varying the repulsion strength, the gel structure and its viscoelastic properties can be largely tuned. In particular, the gel fractal dimension can be either increased or decreased with respect to mechanical equilibrium conditions. Unexpectedly, gels with stronger repulsion, despite being mechanically stiffer, are found to be less viscous with respect to purely attractive ones. We provide a microscopic explanation of these findings in terms of the influence of an underlying phase separation. Our results allow for the design of colloidal gels with desired structure and viscoelastic response by means of additional electrostatic interactions, easily controllable in experiments.
- arXiv:2003.07608 [pdf, other]
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Title: Optimal operation of a three-level quantum heat engine and universal nature of efficiencyAuthors: Varinder SinghSubjects: Statistical Mechanics (cond-mat.stat-mech); Quantum Physics (quant-ph)
We present a detailed study of a three-level quantum heat engine operating at maximum efficient power function, a trade-off objective function defined by the product of the efficiency and power output of the engine. First, for near equilibrium conditions, we find general expression for the efficiency and establish universal nature of efficiency at maximum power and maximum efficient power. Then in the high temperature limit, optimizing with respect to one parameter while constraining the other one, we obtain the lower and upper bounds on the efficiency for both strong as well as weak matter-field coupling conditions. Except for the weak matter-field coupling condition, the obtained bounds on the efficiency exactly match with the bounds already known for some models of classical heat engines. Further for weak matter-field coupling, we derive some new bounds on the the efficiency of the the engine which lie beyond the range covered by bounds obtained for strong matter-field coupling. We conclude by comparing the performance of our three-level quantum heat engine in maximum power and maximum efficient power regimes and show that the engine operating at maximum efficient power produces at least $88.89\%$ of the maximum power output while considerably reducing the power loss due to entropy production.
- arXiv:2003.07614 [pdf, ps, other]
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Title: Universal low-frequency vibrational modes in silica glassesComments: 4 pages, 5 figures, Submitted in parallel to "Universality of the nonphononic vibrational spectrum across different classes of computer glasses" to arXiv on March 17th, 2020Subjects: Soft Condensed Matter (cond-mat.soft); Disordered Systems and Neural Networks (cond-mat.dis-nn); Materials Science (cond-mat.mtrl-sci)
It was recently shown that different simple models of glass formers with binary interactions define a universality class in terms of the density of states of their quasi-localized low-frequency modes. Explicitly, once the hybridization with standard Debye (extended) modes is avoided, a number of such models exhibit a universal density of state, depending on the mode frequencies as $D(\omega) \sim \omega^4$. It is unknown however how wide is this universality class, and whether it also pertains to more realistic models of glass formers. To address this issue we present analysis of the quasi-localized modes in silica, a network glass which has both binary and ternary interactions. We conclude that in 3-dimensions silica exhibits the very same frequency dependence at low frequencies, suggesting that this universal form is a generic consequence of amorphous glassiness.
- arXiv:2003.07616 [pdf, other]
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Title: Universality of the nonphononic vibrational spectrum across different classes of computer glassesAuthors: David Richard, Karina González-López, Geert Kapteijns, Robert Pater, Talya Vaknin, Eran Bouchbinder, Edan LernerComments: 8 pages, 4 figures. Universality is demonstrated also for a Bulk Metallic Glass model (CuZr), updated figures and referencesSubjects: Soft Condensed Matter (cond-mat.soft); Statistical Mechanics (cond-mat.stat-mech)
It has been recently established that the low-frequency spectrum of simple computer glass models is populated by soft, quasilocalized nonphononic vibrational modes whose frequencies $\omega$ follow a gapless, universal distribution ${\cal D}(\omega)\!\sim\!\omega^4$. While this universal nonphononic spectrum has been shown to be robust to varying the glass history and spatial dimension, it has so far only been observed in simple computer glasses featuring radially-symmetric, pairwise interaction potentials. Consequently, the relevance of the universality of nonphononic spectra seen in simple computer glasses to realistic laboratory glasses remains unclear. Here we demonstrate the emergence of the universal $\omega^4$ nonphononic spectrum in a broad variety of realistic computer glass models, ranging from tetrahedral network glasses with three-body interactions, through molecular glasses and glassy polymers, to bulk metallic glasses (BMGs). Taken together with previous observations, our results indicate that the low-frequency nonphononic vibrational spectrum of any glassy solid quenched from a melt features the universal $\omega^4$ law, independently of the nature of its microscopic interactions.
- arXiv:2003.07617 [pdf]
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Title: Anomalous critical point behavior in dilute magnetic semiconductor (Ca,Na)(Zn,Mn)2Sb2Authors: Shuang Yu, Xinyu Liu, Guoqiang Zhao, Yi Peng, Xiancheng Wang, Jianfa Zhao, Wenmin Li, Zheng Deng, Jacek K. Furdyna, Y. J. Uemura, Changqing JinComments: 28 pages, 6figures, 1 tableJournal-ref: Physical Review Materials 4, 024411 (2020)Subjects: Materials Science (cond-mat.mtrl-sci); Strongly Correlated Electrons (cond-mat.str-el)
In this paper we report successful synthesis and magnetic properties of (Ca,Na)(Zn,Mn)2Sb2 as a new ferromagnetic dilute magnetic semiconductor (DMS). In this DMS material the concentration of magnetic moments can be controlled independently from the concentration of electric charge carriers that are required for mediating magnetic interactions between these moments. This feature allows us to separately investigate the effect of carriers and of spins on the ferromagnetic properties of this new DMS alloy, and particularly of the critical ferromagnetic behavior. We use modified Arrott plot technique to establish critical exponents b, g, and d of this alloy. We find that at low Mn concentrations (< 10 at.%), it is governed by short-range 3D-Ising behavior, with experimental values of b, g, and d very close to theoretical 3D-Ising values of 0.325, 1.24, and 4.815. However, as the Mn concentration increases, this DMS material exhibits a mixed-phase behavior, with g retaining its 3D-Ising characteristics, but b crossing over to longer-range mean-field behavior.
- arXiv:2003.07643 [pdf, other]
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Title: Solution landscape of a reduced Landau-de Gennes model on a hexagonComments: 15 pages, 10 figuresSubjects: Mathematical Physics (math-ph); Soft Condensed Matter (cond-mat.soft)
We investigate the solution landscape of a reduced Landau--de Gennes model for nematic liquid crystals on a two-dimensional hexagon at a fixed temperature, as a function of $\lambda$---the edge length. This is a generic example for reduced approaches on regular polygons. We apply the high-index optimization-based shrinking dimer method to systematically construct the solution landscape consisting of multiple defect solutions and relationships between them. We report a new stable T state with index-$0$ that has an interior $-1/2$ defect; new classes of high-index saddle points with multiple interior defects referred to as H class and TD class; changes in the Morse index of saddle points with $\lambda^2$ and novel pathways mediated by high-index saddle points that can control and steer dynamical pathways. The range of topological degrees, locations and multiplicity of defects offered by these saddle points can be used to navigate through complex solution landscapes of nematic liquid crystals and other related soft matter systems.
- arXiv:2003.07662 [pdf, other]
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Title: Degree irregularity and rank probability bias in network meta-analysisComments: 15 pages, 14 figuresSubjects: Methodology (stat.ME); Statistical Mechanics (cond-mat.stat-mech)
Network meta-analysis (NMA) is a statistical technique for the comparison of treatment options. The nodes of the network are the competing treatments and edges represent comparisons of treatments in trials. Outcomes of Bayesian NMA include estimates of treatment effects, and the probabilities that each treatment is ranked best, second best and so on. How exactly network geometry affects the accuracy and precision of these outcomes is not fully understood. Here we carry out a simulation study and find that disparity in the number of trials involving different treatments leads to a systematic bias in estimated rank probabilities. This bias is associated with an increased variation in the precision of treatment effect estimates. Using ideas from the theory of complex networks, we define a measure of `degree irregularity' to quantify asymmetry in the number of studies involving each treatment. Our simulations indicate that more regular networks have more precise treatment effect estimates and smaller bias of rank probabilities. We also find that degree regularity is a better indicator of NMA quality than both the total number of studies in a network and the disparity in the number of trials per comparison. These results have implications for planning future trials. We demonstrate that choosing trials which reduce the network's irregularity can improve the precision and accuracy of NMA outcomes.
- arXiv:2003.07667 [pdf, other]
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Title: Mean-field theory of interacting triplons in a two-dimensional valence-bond solidAuthors: R. L. DorettoComments: 20 pages, 11 figuresSubjects: Strongly Correlated Electrons (cond-mat.str-el); Statistical Mechanics (cond-mat.stat-mech)
We study a system of interacting triplons (the elementary excitations of a valence-bond solid) described by an effective interacting boson model derived within the bond-operator formalism. In particular, we consider the square lattice spin-1/2 $J_1$-$J_2$ antiferromagnetic Heisenberg model, focus on the intermediate parameter region, where a quantum paramagnetic phase sets in, and consider the columnar valence-bond solid phase. Within the bond-operator theory, the Heisenberg model is mapped into an effective boson model in terms of triplet operators $t$. The effective boson model is studied at the harmonic approximation and the energy of the triplons and the expansion of the triplon operators $b$ in terms of the triplet operators $t$ are determined. Such an expansion allows us to performed a second mapping, and therefore, determine an effective interacting boson model in terms of the triplon operators $b$. We then consider systems with a fixed number of triplons and determined the ground-state energy and the spectrum of elementary excitations within a mean-field approximation. We show that many-triplon states are stable, the lowest-energy ones are constituted by a small number of triplons, and the excitation gaps are finite. For $J_2=0.48 J_1$ and $J_2=0.52 J_1$, we also calculate spin-spin and dimer-dimer correlation functions, dimer order parameters, and the bipartite von Neumann entanglement entropy within our mean-field formalism in order to determine the properties of the many-triplon state as a function of the triplon number. We find that the spin and the dimer correlations decay exponentially and that the entanglement entropy obeys an area law, regardless the triplon number. Moreover, only for $J_2=0.48 J_1$, the spin correlations indicate that the many-triplon states with large triplon number might display a more homogeneous singlet pattern than the columnar valence-bond solid.
- arXiv:2003.07673 [pdf, other]
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Title: Active interface polarization is a state functionComments: 6 pages, 1 figureJournal-ref: Phys. Rev. Research 2, 022003(R) (2020)Subjects: Statistical Mechanics (cond-mat.stat-mech); Soft Condensed Matter (cond-mat.soft)
We prove three exact sum rules that relate the polarization of active Brownian particles to their one-body current: (i) The total polarization vanishes, provided that there is no net flux through the boundaries, (ii) at any planar wall the polarization is determined by the magnitude of the bulk current, and (iii) the total interface polarization between phase-separated fluid states is rigorously determined by the gas-liquid current difference. This result precludes the influence of the total interface polarization on active bulk coexistence and questions the proposed coupling of interface to bulk.
- arXiv:2003.07677 [pdf, other]
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Title: Experimental evidence of spin-orbit torque from metallic interfacesAuthors: A. Anadón, R. Guerrero, J. A. Jover-Galtier, A. Gudín, J. M. Díez, P. Olleros-Rodríguez, R. Miranda, J. Camarero, P. PernaComments: 12 pages, 5 figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci)
Spin currents can modify the magnetic state of ferromagnetic ultrathin films through spin-orbit torque. They may be generated by means of spin-orbit interaction by either bulk or interfacial phenomena. Electrical transport measurements reveal a six-fold increase of the spin-orbit torque accompanied by a drastic reduction of the spin Hall magnetoresistance upon the introduction of a Cu interlayer in a Pt/Cu/Co/Pt structure with perpendicular magnetic anisotropy. We analyze the dependence of the spin Hall magnetoresistance with the thickness of the interlayer in the frame of a drift diffusion model that provides information on the expected spin currents and spin accumulations in the system. The results demonstrate that the major responsible of both effects is spin memory loss at the interface. The enhancement of the spin-orbit torque when introducing an interlayer opens the possibility to design more effient spintronic devices based on materials that are cheap and abundant such as copper.
- arXiv:2003.07686 [pdf]
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Title: Giant Grüneisen parameter in a strain-tuned superconducting quantum paraelectric: A consequence of the vanishing ferroelectric phonon energyAuthors: Jacob Franklin, Bochao Xu, Donovan Davino, Alexander V. Balatsky, Ulrich Aschauer, Ilya SochnikovSubjects: Superconductivity (cond-mat.supr-con)
Superconductivity and ferroelectricity are typically incompatible because the former needs free carriers, but the latter is usually suppressed by free carriers, unless their concentration is low. In the case of strontium titanate with low carrier concentration, unconventional superconductivity and ferroelectricity were shown to be correlated. Here, we report theoretically and experimentally evaluated Gr\"uneisen parameters whose divergence under tensile stress indicates that the dominant phonon mode that enhances the superconducting order is the ferroelectric transverse soft-mode. This finding rules out all other phonon modes as the main contributors to the enhanced superconductivity in strained strontium titanate. This methodology shown here can be applied to many other quantum materials.
- arXiv:2003.07702 [pdf]
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Title: A femto-Tesla DC SQUID design for quantum-ready readoutsComments: This version of the manuscript is to be published in Physical Review AppliedSubjects: Superconductivity (cond-mat.supr-con); Quantum Physics (quant-ph)
Among some of the current uses of the DC Superconducting QUantum Interference Devices (SQUIDs) are qubit-readouts and sensors for probing properties of quantum materials. We present a rather unique gradiometric niobium SQUID design with state-of-the-art sensitivity in the femto-Tesla range which can be easily tuned to specific readout requirements. The sensor is a next generation of the fractional SQUIDs with tightly optimized input coil and a combination of all measures known for restraining parasitic resonances and other detrimental effects. Our design combines the practical usefulness of well-defined pickup loops for superior imaging kernel and tunable-probing applications with the fractionalization approach to reduce undesired inductances. In addition, our modeling predicts small dimensions for these planar sensors. These features make them of high relevance for material studies and for detection of magnetic fields in small volumes, e.g. as part of a cryogenic scanning quantum imaging apparatus for efficient diagnostics and quantum device readouts. This manuscript will benefit scientists and engineers working on quantum computing technologies by clarifying potential general misconceptions about DC SQUID optimization alongside the introduction of the novel flexible compact DC SQUID design.
- arXiv:2003.07712 [pdf]
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Title: Observation of giant spin-split Fermi-arc with maximal Chern number in the chiral topological semimetal PtGaAuthors: Mengyu Yao, Kaustuv Manna, Qun Yang, Alexander Fedorov, Vladimir Voroshnin, B. Valentin Schwarze, Jacob Hornung, S. Chattopadhyay, Zhe Sun, Satya N Guin, Jochen Wosnitza, Horst Borrmann, Chandra Shekhar, Nitesh Kumar, Jörg Fink, Yan Sun, Claudia FelserComments: Accepted in Nature CommunicationsJournal-ref: Nature Communications, volume 11, Article number: 2033 (2020)Subjects: Materials Science (cond-mat.mtrl-sci); Strongly Correlated Electrons (cond-mat.str-el)
Non-symmorphic chiral topological crystals host exotic multifold fermions, and their associated Fermi arcs helically wrap around and expand throughout the Brillouin zone between the high-symmetry center and surface-corner momenta. However, Fermi-arc splitting and realization of the theoretically proposed maximal Chern number rely heavily on the spin-orbit coupling (SOC) strength. In the present work, we investigate the topological states of a new chiral crystal, PtGa, which has the strongest SOC among all chiral crystals reported to date. With a comprehensive investigation using high-resolution angle-resolved photoemission spectroscopy, quantum-oscillation measurements, and state-of-the-art ab initio calculations, we report a giant SOC-induced splitting of both Fermi arcs and bulk states. Consequently, this study experimentally confirms the realization of a maximal Chern number equal to |4| for the first time in multifold fermionic systems, thereby providing a platform to observe large-quantized photogalvanic currents in optical experiments.
- arXiv:2003.07721 [pdf]
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Title: Domain wall dynamics in stepped magnetic nanowire with perpendicular magnetic anisotropySubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Micromagnetic simulation is carried out to investigate the current-driven domain wall (DW) in a nanowire with perpendicular magnetic anisotropy (PMA). A stepped nanowire is proposed to pin DW and achieve high information storage capacity based on multi-bit per cell scheme. The DW speed is found to increase for thicker and narrower nanowires. For depinning DW from the stepped region, the current density Jdep is investigated with emphasis on device geometry and materials intrinsic properties. The Jdep could be analytically determined as a function of the nanocontriction dimension and the thickness of the nanowire. Furthermore, Jdep is found to exponential dependent on the anisotropy energy and saturation magnetization, offering thus more flexibility in adjusting the writing current for memory applications.
- arXiv:2003.07722 [pdf]
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Title: Magnetic dipole absorption at intersubband transitions in quantum wellsComments: 10 pages, 2 figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Optics (physics.optics)
We consider theoretically magnetic dipole mechanism of light absorption at intersubband transitions in wide-gap quantum wells (QW). In contrast to electric dipole resonance, discussed mechanism manifests in the interaction with s-polarized component of electromagnetic radiation. Magnetic dipole resonance leads to relatively weak absorption, but it should be measurable against the background of much stronger electric dipole absorption because of the absence of frequency shift due to collective plasma effects. It also means that the observation of these dipole resonances of both types may become an experimental method of characterization of QW potential profile.
- arXiv:2003.07724 [pdf]
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Title: Modelling the size of Nitrogen c(2x2) islands on Cu(001) with elastic multisite interactionsAuthors: Wolfgang KappusComments: 15 pages, 5 figures, changes marked in Purple Color. arXiv admin note: text overlap with arXiv:1907.08929Subjects: Materials Science (cond-mat.mtrl-sci); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
An extended elastic eigenvector approach for adatom interactions is applied to model Nitrogen c(2x2) Atom islands on Cu(001). Oscillating interactions between adatom monomers or dimers are considered. Attractive pair interactions of adatoms are able to describe agglomeration but fail to explain the size of islands. Multisite interactions created by dimers, however, can explain the size of islands if an interaction parameter is adjusted properly. Finite size islands are formed when repulsive monomer interactions are balanced by attractive monomer-dimer interactions. A simple model of nearest neighbour attraction and s-3 repulsion is used as an example for the interaction parameter search. Previous experimental studies have shown that in the low coverage region Nitrogen atoms agglomerate to isolated square islands of about 5 nm x 5 nm size with a c(2x2) structure. With increasing coverage those islands form regular patterns but do not touch below about 0.4 monolayers. Previous experiments and calculations have shown that the square island pattern show significant elastic effects. Different adatom structures within the Nitrogen islands have been analyzed, a dimer step model is able to reproduce the experimentally found island size. This model requires a molecular bond between dimers formed by Nitrogen adatoms. The model is also used to compute elastic interactions between islands and to check it against the experimentally found island pattern. Shortcomings and limitations of the model are discussed and open questions are formulated.
- arXiv:2003.07750 [pdf]
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Title: Electrical generation and detection of terahertz signal based on spin-wave emission from ferrimagnetsAuthors: Zhifeng Zhu, Kaiming Cai, Jiefang Deng, Venkata Pavan Kumar Miriyala, Hyunsoo Yang, Xuanyao Fong, Gengchiau LiangJournal-ref: Phys. Rev. Applied 13, 034040 2020Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Terahertz (THz) signals, mainly generated by photonic or electronic approaches, are being sought for various applications, whereas the development of magnetic source might be a necessary step to harness the magnetic nature of electromagnetic radiation. We show that the relativistic effect on the current-driven domain-wall motion induces THz spin-wave emission in ferrimagnets. The required current density increases dramatically in materials with strong exchange interaction and rapidly exceeds 1012 A m-2, leading to the device breakdown and thus the lack of experimental evidence. By translating the collective magnetization oscillations into voltage signals, we propose a three-terminal device for the electrical detection of THz spin wave. Through material engineering, wide frequency range from 264 GHz to 1.1 THz and uniform continuous signals with improved output power can be obtained. As a reverse effect, the spin wave generated in this system is able to move ferrimagnetic domain wall. Our work provides guidelines for the experimental verification of THz spin wave, and could stimulate the design of THz spintronic oscillators for wideband applications as well as the all-magnon spintronic devices.
- arXiv:2003.07752 [pdf, other]
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Title: Automated calculation and convergence of defect transport tensorsSubjects: Computational Physics (physics.comp-ph); Materials Science (cond-mat.mtrl-sci); Statistical Mechanics (cond-mat.stat-mech); Data Analysis, Statistics and Probability (physics.data-an)
Defect transport is a key process in materials science and catalysis, but as migration mechanisms are often too complex to enumerate a priori, calculation of transport tensors typically have no measure of convergence and require significant end user intervention. These two bottlenecks prevent high-throughput implementations essential to propagate model-form uncertainty from interatomic interactions to predictive simulations. In order to address these issues, we extend a massively parallel accelerated sampling scheme, autonomously controlled by Bayesian estimators of statewise sampling completeness, to build atomistic kinetic Monte Carlo models on a state space irreducible under exchange and space group symmetries. Focusing on isolated defects, we derive analytic expressions for defect transport tensors and provide a convergence metric by calculating the Kullback-Leiber divergence across the ensemble of diffusion processes consistent with the sampling uncertainty. The autonomy and efficacy of the method is demonstrated on surface trimers in tungsten and hexa-interstitials in magnesium oxide, both of which exhibit complex, correlated migration mechanisms.
- arXiv:2003.07753 [pdf, other]
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Title: Adversarial Reverse Mapping of Equilibrated Condensed-Phase Molecular StructuresComments: 11 pages, 6 figuresSubjects: Soft Condensed Matter (cond-mat.soft); Chemical Physics (physics.chem-ph); Computational Physics (physics.comp-ph)
A tight and consistent link between resolutions is crucial to further expand the impact of multiscale modeling for complex materials. We herein tackle the generation of condensed molecular structures as a refinement -- backmapping -- of a coarse-grained structure. Traditional schemes start from a rough coarse-to-fine mapping and perform further energy minimization and molecular dynamics simulations to equilibrate the system. In this study we introduce DeepBackmap: A deep neural network based approach to directly predict equilibrated molecular structures for condensed-phase systems. We use generative adversarial networks to learn the Boltzmann distribution from training data and realize reverse mapping by using the coarse-grained structure as a conditional input. We apply our method to a challenging condensed-phase polymeric system. We observe that the model trained in a melt has remarkable transferability to the crystalline phase. The combination of data-driven and physics-based aspects of our architecture help reach temperature transferability with only limited training data.
- arXiv:2003.07755 [pdf, other]
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Title: A Tug-of-War in a Double-Nanopore SystemComments: 8 Pages, 7 figuresSubjects: Soft Condensed Matter (cond-mat.soft)
We simulate a tug-of-war (TOW) scenario for a model double-stranded DNA threading through a double nanopore (DNP) system. The DNA, simultaneously captured at both pores is subject to two equal and opposite forces $-\vec{f}_L= \vec{f}_R$ (TOW), where $\vec{f}_L$ and $\vec{f}_R$ are the forces applied to the left and the right pore respectively. Even though the net force on the DNA polymer $\Delta \vec{f}_{LR}=\vec{f}_L+ \vec{f}_R=0$, the mean first passage time (MFPT) $\langle \tau \rangle$ depends on the magnitude of the TOW forces $ \left | f_L \right | = \left |f_R \right | = f_{LR}$. We qualitatively explain this dependence of $\langle \tau \rangle$ on $f_{LR}$ from the known results for the single-pore translocation of a triblock copolymer. We demonstrate that the time of flight (TOF) of a monomer with index $m$ ($\langle \tau_{LR}(m) \rangle$) from one pore to the other exhibits quasi-periodic structure commensurate with the distance between the pores $d_{LR}$. Finally, we study the case $\Delta \vec{f}_{LR}=\vec{f}_L+ \vec{f}_R \ne 0$, and qualitatively reproduce the experimental result of the dependence of the MFPT on $\Delta\vec{f}_{LR}$. For a moderate bias, the MFPT for the DNP system for a chain length $N$ follows the same scaling ansatz as that of for the single nanopore, $\langle \tau \rangle = \left( AN^{1+\nu} + \eta_{pore}N \right) \left(\Delta f_{LR}\right)^{-1}$, where $\eta_{pore}$ is the pore friction, which enables us to estimate $\langle \tau \rangle $ for a long chain. Our Brownian dynamics simulation studies provide fundamental insights and valuable information about the details of the translocation speed obtained from $\langle \tau_{LR}(m) \rangle$, and accuracy of the translation of the data obtained in the time-domain to units of genomic distances.
- arXiv:2003.07757 [pdf]
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Title: Black phosphorus van der Waals heterostructures light emitting diodes for mid-infrared silicon photonicsAuthors: Tian-Yun Chang, Yueyang Chen, De-In Luo, Jia-Xin Li, Po-Liang Chen, Seokhyeong Lee, Zhuoran Fang, Wei-Qing Li, Ya-Yun Zhang, Mo Li, Arka Majumdar, Chang-Hua LiuComments: 12 pages, 4 figuresSubjects: Applied Physics (physics.app-ph); Materials Science (cond-mat.mtrl-sci)
Light-emitting diodes (LEDs) based on III-V/II-VI materials have delivered a compelling performance in the mid-infrared (mid-IR) region, which enabled wide-ranging applications, including environmental monitoring, defense and medical diagnostics. Continued efforts are underway to realize on-chip sensors via heterogeneous integration of mid-IR emitters on a silicon photonic chip. But the uptake of such approach is limited by the high costs and interfacial strains, associated with the process of heterogeneous integrations. Here, the black phosphorus (BP)-based van der Waals (vdW) heterostructures are exploited as room temperature LEDs. The demonstrated devices can emit linearly polarized light, and their spectra cover the technologically important mid-IR atmospheric window (3-4 um). Additionally, the BP LEDs exhibit fast modulation speed as well as exceptional stability, and its peak extrinsic quantum efficiency (QE~0.9%) is comparable to the III-V/II-VI mid-IR LEDs. By leveraging the integrability of vdW heterostructures, we further demonstrate a silicon photonic waveguide-integrated BP LED. The reported hybrid platform holds great promise for mid-IR silicon photonics.
- arXiv:2003.07763 [pdf, other]
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Title: Synchronous whirling of spinning homogeneous elastic cylinders: linear and weakly non-linear analysesAuthors: S. MoraSubjects: Soft Condensed Matter (cond-mat.soft)
Stationary whirling of slender and homogeneous (continuous) elastic shafts rotating around their axis, with pin-pin boundary condition at the ends, is revisited by considering the complete deformations in the cross section of the shaft. The stability against a synchronous sinusoidal disturbance of any wave length is investigated and the analytic expression of the buckling amplitude is derived in the weakly non-linear regime by considering both geometric and material (hyper-elastic) non-linearities. The bifurcation is super-critical in the long wave length domain for any elastic constitutive law, and sub-critical in the short wave length limit for a limited range of non-linear material parameters.
- arXiv:2003.07767 [pdf, other]
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Title: Effects of deterministic disorder at deeply subwavelength scales in multilayered dielectric metamaterialsComments: 11 pages; 6 figuresSubjects: Optics (physics.optics); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci)
It is common understanding that multilayered dielectric metamaterials, in the regime of deeply subwavelength layers, are accurately described by simple effective-medium models based on mixing formulas that do not depend on the spatial arrangement. In the wake of recent studies that have shown counterintuitive examples of periodic and aperiodic (orderly or random) scenarios in which this premise breaks down, we study here the effects of deterministic disorder. With specific reference to a model based on Golay-Rudin-Shapiro sequences, we illustrate certain peculiar boundary effects that can occur in finite-size dielectric multilayers, leading to anomalous light-transport properties that are in stark contrast with the predictions from conventional effective-medium theory. Via parametric and comparative studies, we elucidate the underlying physical mechanisms, also highlighting similarities and differences with respect to previously studied geometries. Our outcomes may inspire potential applications to optical sensing, switching and lasing.
- arXiv:2003.07771 [pdf, other]
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Title: From flat to tilted: gradual interfaces in organic thin film growthAuthors: Laura Katharina Scarbath-Evers, René Hammer, Dorothea Golze, Martin Brehm, Daniel Sebastiani, Wolf WiddraJournal-ref: Nanoscale, 12:3834 (2020)Subjects: Materials Science (cond-mat.mtrl-sci); Computational Physics (physics.comp-ph)
We investigate domain formation and local morphology of thin films of $\alpha$-sexithiophene ($\alpha$-6T) on Au(100) beyond monolayer coverage by combining high resolution scanning tunneling microscopy (STM) experiments with electronic structure theory calculations and computational structure search. We report a layerwise growth of highly-ordered enantiopure domains. For the second and third layer, we show that the molecular orbitals of individual $\alpha$-6T molecules can be well resolved by STM, providing access to detailed information on the molecular orientation. We find that already in the second layer the molecules abandon the flat adsorption structure of the monolayer and adopt a tilted conformation. Although the observed tilted arrangement resembles the orientation of $\alpha$-6T in the bulk, the observed morphology does not yet correspond to a well-defined surface of the $\alpha$-6T bulk structure. A similar behavior is found for the third layer indicating a growth mechanism where the bulk structure is gradually adopted over several layers.
- arXiv:2003.07795 [pdf, ps, other]
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Title: Time-dependent entropy of a cooling Bose gasAuthors: Georg WolschinComments: 7 pages, 4 figures, as accepted by EPLJournal-ref: EPL 129, 40006 (2020)Subjects: Quantum Gases (cond-mat.quant-gas); Exactly Solvable and Integrable Systems (nlin.SI)
Exact analytic solutions of a nonlinear boson diffusion equation with suitable initial conditions that account for evaporative cooling of ultracold atoms, plus boundary conditions at the singularity $\epsilon=\mu<0$ are presented, and used to calculate the time-dependent entropy of a cold quantum gas.
- arXiv:2003.07804 [pdf]
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Title: Atomic Scale Insights Into The Mechanical Characteristics of Monolayer 1T-Titanium Disulphide: A Molecular Dynamics StudyAuthors: Tanmay Sarkar Akash (1), Rafsan A.S.I. Subad (1), Pritom Bose (1), Md Mahbubul Islam (2 and 3) ((1) Department of Mechanical Engineering, Bangladesh University of Engineering and Technology, Dhaka-1000, Bangladesh. (2) Department of Mechanical Engineering, Wayne State University, MI, USA (3) Corresponding Author)Comments: ALL AUTHORS CONTRIBUTED EQUALLYSubjects: Materials Science (cond-mat.mtrl-sci)
In this work, we report on the mechanical responses and fracture behavior of pristine and defected monolayer 1T-Titanium Disulfide using classical molecular dynamics simulation. We investigated the effect of temperature, strain rate and defect ratio on the uniaxial tensile properties in both armchair and zigzag direction. We found that monolayer TiS2 shows isotropic uniaxial tensile properties except for failure strain which is greater in zigzag direction than armchair direction. We also observed a negative correlation of ultimate tensile strength, failure strain and young's modulus with temperature and defect ratio. Results depicts that strain rate has no effect on the young's modulus of monolayer TiS2 but higher strain rate results in higher ultimate tensile strength and failure strain.
- arXiv:2003.07812 [pdf, other]
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Title: Phase diagram of the $\mathbb{Z}_3$-Fock parafermion chain with pair hoppingSubjects: Strongly Correlated Electrons (cond-mat.str-el); Other Condensed Matter (cond-mat.other)
We study a tight binding model of $\mathbb{Z}_3$-Fock parafermions with single-particle and pair-hopping terms. The phase diagram has four different phases: a gapped phase, a gapless phase with central charge $c=2$, and two gapless phases with central charge $c=1$. We characterise each phase by analysing the energy gap, entanglement entropy and different correlation functions. The numerical simulations are complemented by analytical arguments.
- arXiv:2003.07826 [pdf, other]
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Title: A simple, general criterion for onset of disclination disorder on curved surfacesSubjects: Soft Condensed Matter (cond-mat.soft)
Determining the positions of lattice defects on elastic surfaces with Gaussian curvature is a non-trivial task of mechanical energy optimization, particularly for surfaces with boundaries. We introduce a simple way to predict the onset of disclination disorder from the shape of bounded surfaces. The criterion fixes the value of a weighted integral Gaussian curvature to a universal constant and proves accurate across a great variety of shapes, even when previously suggested criteria fail. It is an easy avenue to improved understanding of the limitations to crystalline order in many materials.
- arXiv:2003.07829 [pdf, other]
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Title: Fingerprints of the local moment formation and its Kondo screening in the generalized susceptibilities of many-electron problemsSubjects: Strongly Correlated Electrons (cond-mat.str-el)
We identify the precise hallmarks of the local magnetic moment formation and its Kondo screening in the frequency structure of the generalized charge susceptibility. The sharpness of our identification even pinpoints a novel criterion to determine the Kondo temperature of strongly correlated systems on the two-particle level, which only requires calculations at the {\sl lowest} Matsubara frequency. We showcase its strength by applying it to the single impurity and the periodic Anderson model as well as to the Hubbard model. Our results represent a significant progress for the general understanding of quantum field theory at the two-particle level and allow for tracing the limits of the physics captured by perturbative approaches in correlated regimes.
- arXiv:2003.07834 [pdf, other]
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Title: Fractional viscoelastic models for power-law materialsComments: 28 pages, 12 figuresSubjects: Soft Condensed Matter (cond-mat.soft); Biological Physics (physics.bio-ph); Quantitative Methods (q-bio.QM); Tissues and Organs (q-bio.TO)
Soft materials often exhibit a distinctive power-law viscoelastic response arising from broad distribution of time-scales present in their complex internal structure. A promising tool to accurately describe the rheological behaviour of soft materials is fractional calculus. However, its use in the scientific community remains limited due to the unusual notation and non-trivial properties of fractional operators. This review aims to provide a clear and accessible description of fractional viscoelastic models for a broad audience, and to demonstrate the ability of these models to deliver a unified approach for the characterisation of power-law materials. The use of a consistent framework for the analysis of rheological data would help classify the empirical behaviours of soft and biological materials, and better understand their response.
- arXiv:2003.07844 [pdf, other]
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Title: Tunable deconfined quantum criticality and interplay of different valence-bond solid phasesComments: 14 pages, 14 figuresSubjects: Strongly Correlated Electrons (cond-mat.str-el)
We use quantum Monte Carlo simulations to study a quantum $S=1/2$ spin model with competing multi-spin interactions. We find a quantum phase transition between a columnar valence-bond solid (cVBS) and a N\'eel antiferromagnet (AFM), as in the scenario of deconfined quantum-critical points, as well as a transition between the AFM and a staggered valence-bond solid (sVBS). By continuously varying a parameter, the sVBS--AFM and AFM--cVBS boundaries merge into a direct sVBS--cVBS transition. Unlike previous models with putative deconfined AFM--cVBS transitions, e.g., the standard $J$-$Q$ model, in our extended $J$-$Q$ model with competing cVBS and sVBS inducing terms the transition can be tuned from continuous to first-order. We find the expected emergent U(1) symmetry of the microscopically $Z_4$ symmetric cVBS order parameter when the transition is continuous. In contrast, when the transition changes to first-order the clock-like $Z_4$ fluctuations are absent and there is no emergent higher symmetry. We argue that the confined spinons in the sVBS phase are fracton-like. We also present results for an SU(3) symmetric model with a similar phase diagram. The new family of models can serve as a useful tool for further investigating open questions related to deconfined quantum criticality and its associated emergent symmetries.
- arXiv:2003.07850 [pdf, other]
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Title: Forming a single molecule by magnetoassociation in an optical tweezerAuthors: Jessie T. Zhang, Yichao Yu, William B. Cairncross, Kenneth Wang, Lewis R. B. Picard, Jonathan D. Hood, Yen-Wei Lin, Jeremy M. Hutson, Kang-Kuen NiSubjects: Atomic Physics (physics.atom-ph); Quantum Gases (cond-mat.quant-gas); Chemical Physics (physics.chem-ph)
We demonstrate the formation of a single NaCs molecule in an optical tweezer by magnetoassociation through an s-wave Feshbach resonance at 864.11(5)G. Starting from single atoms cooled to their motional ground states, we achieve conversion efficiencies of 47(1)%, and measure a molecular lifetime of 4.7(7)ms. By construction, the single molecules are predominantly (77(5)%) in the center-of-mass motional ground state of the tweezer. Furthermore, we produce a single p-wave molecule near 807G by first preparing one of the atoms with one quantum of motional excitation. Our creation of a single weakly bound molecule in a designated internal state in the motional ground state of an optical tweezer is a crucial step towards coherent control of single molecules in optical tweezer arrays.
- arXiv:2003.07851 [pdf, other]
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Title: Local Probes for Quantum Hall Ferroelectrics and NematicsComments: Main: 5 pages, 4 figures; Supplement: 9 pages, 4 figures; published versionJournal-ref: Phys. Rev. B 101, 241103(R) (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Two-dimensional multi-valley electronic systems in which the dispersion of individual pockets has low symmetry give rise to quantum Hall ferroelectric and nematic states in the presence of strong quantising magnetic fields. We investigate local signatures of these states arising near impurities that can be probed via Scanning Tunnelling Microscopy (STM) spectroscopy. For quantum Hall ferroelectrics, we demonstrate a direct relation between the dipole moment measured at impurity bound states and the ideal bulk dipole moment obtained from the modern theory of polarisation. We also study the many-body problem with a single impurity via exact diagonalization and find that near strong impurities non-trivial excitonic state can form with specific features that can be easily identified via STM spectroscopy.
Replacements
- arXiv:1704.04045 (replaced) [pdf, other]
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Title: Observation of Volkov-Pankratov states in topological HgTe heterojunctions using high-frequency compressibilityAuthors: A. Inhofer, S. Tchoumakov, B.A. Assaf, G. Fève, J.M. Berroir, V. Jouffrey, D. Carpentier, M. Goerbig, B. Plaçais, K. Bendias, D.M. Mahler, E. Bocquillon, R. Schlereth, C. Brüne, H. Buhmann, L.W. MolenkampComments: 29 pages, 8 figuresJournal-ref: Phys. Rev. B 96, 195104 (2017)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
It is well established that topological insulators sustain Dirac fermion surface states as a consequence of band inversion in the bulk. These states have a helical spin polarization and a linear dispersion with large Fermi velocity. In this article we report on a set of experimental observations indicating the existence of massive surface states. These states are confined at the interface and dominate equilibrium and transport properties at high energy and/or high electric field. By monitoring the AC admittance of HgTe topological insulator field-effect capacitors, we access the compressibility and conductivity of surface states in a broad range of energy and electric fields. The Dirac surface states are characterized by a compressibility minimum, a linear energy dependence and a high mobility persisting up to energies much larger than the transport bandgap of the bulk. New features are revealed at high energies with signatures such as conductance peaks, compressibility bumps, a strong charge metastability and a Hall resistance anomaly. These features point to the existence of excited massive surface states, responsible for a strong intersubband scattering with the Dirac states and the nucleation of metastable bulk carriers. The spectrum of excited states agrees with predictions of a phenomenological model of the topological-trivial semiconductor interface. The model accounts for the finite interface depth and the effect of electric fields. The existence of excited topological states is essential for the understanding of topological phases and opens a route for engineering and exploiting topological resources in quantum technology.
- arXiv:1801.02663 (replaced) [pdf, ps, other]
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Title: Fermion Loops, Linear Magnetoresistance, Linear In Temperature Resistance, and Bad MetalsAuthors: Vincent SackstederSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Superconductivity (cond-mat.supr-con)
Bad metals including the high $T_c$ superconductors display an exotic resistance that is linear in both temperature and magnetic field. This hallmark of strong correlations is poorly understood. We show that Fourier transforming the magnetoconductance with respect to magnetic field obtains a curve describing the area distribution of loops traced by electrons and holes within the sample. Analysis of this area distribution reveals that linear resistance is caused by scattering and quantum interference, but with more large loops than occur in ordinary 2-D and 3-D materials where scattering destroys quantum coherence and limits loop size. This limit on quantum coherence is absent in linear resistance materials, resulting in larger loops limited only by thermal decoherence. Linear resistance signals that quantum coherence is maintained in the presence of scattering.
- arXiv:1807.00472 (replaced) [pdf, ps, other]
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Title: Linear algebraic structure of zero-determinant strategies in repeated gamesComments: 19 pages, 2 figuresJournal-ref: PLoS ONE 15(4): e0230973 (2020)Subjects: Computer Science and Game Theory (cs.GT); Statistical Mechanics (cond-mat.stat-mech); Physics and Society (physics.soc-ph)
Zero-determinant (ZD) strategies, a recently found novel class of strategies in repeated games, has attracted much attention in evolutionary game theory. A ZD strategy unilaterally enforces a linear relation between average payoffs of players. Although existence and evolutional stability of ZD strategies have been studied in simple games, their mathematical properties have not been well-known yet. For example, what happens when more than one players employ ZD strategies have not been clarified. In this paper, we provide a general framework for investigating situations where more than one players employ ZD strategies in terms of linear algebra. First, we theoretically prove that a set of linear relations of average payoffs enforced by ZD strategies always has solutions, which implies that incompatible linear relations are impossible. Second, we prove that linear payoff relations are independent of each other under some conditions. These results hold for general games with public monitoring including perfect-monitoring games. Furthermore, we provide a simple example of a two-player game in which one player can simultaneously enforce two linear relations, that is, simultaneously control her and her opponent's average payoffs. All of these results elucidate general mathematical properties of ZD strategies.
- arXiv:1903.01276 (replaced) [pdf]
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Title: High-resolution Resonance Spin-flip Raman Spectroscopy of Pairs of Manganese Ions in CdTeAuthors: Cherbunin R.V., Litviak V.M., Ryzhov I.I., Koudinov A.V., Elsässer S., Knapp A., Kiessling T., Geurts J., Chusnutdinow S., Wojtowicz T., Karczewski GComments: 11 pages, 2 figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We report the observation of tens of minor lines of the combinational spin-flip Raman scattering in a CdTe:Mn quantum well by means of the high-resolution optical spectroscopy. Classification of this manifold leads to four characteristic values of energy, that correspond to four different types of pair clusters of Mn ions: the nearest, second, third etc. neighbors. All the four energies show up in a single experiment with a very high precision, providing experimental grounds for a deeper understanding of the d-d exchange interactions in a diluted magnetic semiconductor and demonstrating the capacity of the employed method. The major (nearest-neighbor) exchange constant J_1 = 6.15 K was found to consent with its previously reported value. Other detected characteristic energies are as follows: J_{(2)} = 1.80 K, J_{(3)} = 1.39 K, J_{(4)} = 0.81 K.
- arXiv:1905.01129 (replaced) [pdf, other]
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Title: Control of unlocalized optical nonlinear processes via plasmonic path interferenceComments: 6 pages, 4 figuresSubjects: Optics (physics.optics); Materials Science (cond-mat.mtrl-sci)
Fano resonances can be used to control nonlinear optical processes taking place in the vicinity of a plasmonic hotspot. On top of localization, an extra enhancement appears due to path interference. This scheme, widely studied in the literature, however, has a limited use in practical implementations since substantial frequency conversions actually take place in nonlinear crystals. Here, we raise a different question. Can we control "unlocalized" nonlinear processes, taking place along a crystal body, using path interference effects? We consider metal nanoparticle-quantum emitter dimers embedded in a nonlinear crystal. As our analytical model reveals a rich interference scheme, in parallel, FEM simulations yield a 3-order of magnitude nonlinearity enhancement at the crystal "output" without a remarkable linear and nonlinear enhancement in the "crystal body". Analytical model agrees with the FEM simulations very well. The phenomenon can both be used to enhance frequency conversion without heating the crystal and to provide an additional Fano enhancement on top of the well-known enhancement due to localization.
- arXiv:1905.08763 (replaced) [pdf, other]
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Title: Effective Potential for Emergent Majorana Fermions in Superconductor SystemsComments: 6 pages, 3 figures, Accepted in Physics Letters ASubjects: Strongly Correlated Electrons (cond-mat.str-el); Superconductivity (cond-mat.supr-con)
Majorana fermions cannot be found in nature as a free fundamental particle. Nevertheless, in condensed matter systems, they can emerge as a collective excitation. In this work, using functional integration techniques, we calculated the effective potential for emergent Majorana fermions in the Kitaev chain. In this case, we have shown how the superconductor parameter behaves as a function of temperature. Furthermore, we considered surface-induced superconductivity in a Topological Insulator and calculated the effective potential for emergent Majorana fermions in this system. In the case of an s-wave superconductor, we obtained a gap equation equivalent to that one appearing in a quasi-two-dimensional Dirac electronic system, a candidate to explain high-Tc superconductivity. Finally, for the p-wave superconductor, we have obtained a critical value of the electronelectron interaction in the surface of the Topological Insulator, determining the existence or not of induced superconductivity, a remarkable result to guide experiments
- arXiv:1907.07557 (replaced) [pdf, other]
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Title: Liouville-type equations for the n-particle distribution functions of an open systemSubjects: Mathematical Physics (math-ph); Statistical Mechanics (cond-mat.stat-mech); Computational Physics (physics.comp-ph)
In this work we derive a mathematical model for an open system that exchanges particles and momentum with a reservoir from their joint Hamiltonian dynamics. The complexity of this many-particle problem is addressed by introducing a countable set of n-particle phase space distribution functions just for the open subsystem, while accounting for the reservoir only in terms of statistical expectations. From the Liouville equation for the full system we derive a set of coupled Liouville-type equations for the n-particle distributions by marginalization with respect to reservoir states. The resulting equation hierarchy describes the external momentum forcing of the open system by the reservoir across its boundaries, and it covers the effects of particle exchanges, which induce probability transfers between the n- and (n+1)-particle distributions. Similarities and differences with the Bergmann-Lebowitz model of open systems (P.G.Bergmann, J.L. Lebowitz, Phys.Rev., 99:578--587 (1955)) are discussed in the context of the implementation of these guiding principles in a computational scheme for molecular simulations.
- arXiv:1907.12863 (replaced) [pdf, other]
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Title: Oriented propagation of magnetization due to chiral edge modes in Kitaev-type modelsComments: 19 pages, 7 figuresJournal-ref: Phys. Rev. B 101, 014442 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el); Mathematical Physics (math-ph)
Detecting chiral edge modes in topological materials has been intensively pursued in experiments. However, the phenomena caused by the modes are not yet elucidated theoretically. We study the dynamics of chiral spinon wave packets at the edge in Kitaev-type magnets. More precisely, by relying on the exact solvability of the models, we construct a spinon wave packet, localized edge magnetization, which shows oriented propagation along the edge, whose behavior is expected from the chiral character of the dispersion relation of the chiral edge modes. In general, this approach enables us to study not only spin transport in anisotropic magnets but also charge transport in Bogoliubov-de Gennes-type superconductors because it does not rely on a conserved quantity.
- arXiv:1908.06984 (replaced) [pdf, ps, other]
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Title: On duality between Cosserat elasticity and fractonsComments: 16 pagesJournal-ref: SciPost Phys. 8, 065 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el); High Energy Physics - Theory (hep-th)
We present a dual formulation of the Cosserat theory of elasticity. In this theory a local element of an elastic body is described in terms of local displacement and local orientation. Upon the duality transformation these degrees of freedom map onto a coupled theory of a vector-valued one-form gauge field and an ordinary $U(1)$ gauge field. We discuss the degrees of freedom in the corresponding gauge theories, the defect matter and coupling to the curved space.
- arXiv:1908.07090 (replaced) [pdf, ps, other]
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Title: On the hydrodynamic canonical formalism of the Gross-Pitaevskii fieldComments: 8 pages. Comments welcomeSubjects: Quantum Gases (cond-mat.quant-gas)
We derive a canonical formalism for the hydrodynamic representation of the Gross-Pitaevskii field (nonlinear Schr\"odinger field), where the density and the phase of the condensate form a canonical pair of conjugate field variables. To do so, we treat the meanfield as a singular Lagrangian system and apply both the Dirac-Bergmann and Faddeev-Jackiw methods. The Faddeev-Jackiw method is found to be a more direct approach to the problem.
- arXiv:1908.08604 (replaced) [pdf, other]
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Title: Semiclassical Dispersion Corrections efficiently improve Multi-Configurational Theory with Short-Range Density-Functional Dynamic CorrelationComments: 19 pages, 2 figures, 1 tableJournal-ref: J. Phys. Chem. A 2020, 124, 2834-2841Subjects: Chemical Physics (physics.chem-ph); Materials Science (cond-mat.mtrl-sci); Strongly Correlated Electrons (cond-mat.str-el); Computational Physics (physics.comp-ph)
Multi-configurational wave functions are known to describe electronic structure across a Born-Oppenheimer surface qualitatively correct. However, for quantitative reaction energies, dynamical correlation originating from the many configurations involving excitations out of the restricted orbital space, the active space, must be considered. Standard procedures involve approximations that eventually limit the ultimate accuracy achievable (most prominently, multi-reference perturbation theory). At the same time, the computational cost increase dramatically due to the necessity to obtain higher-order reduced density matrices. It is this disproportion that leads us here to propose a MC-srDFT-D hybrid approach of semiclassical dispersion (D) corrections to cover long-range dynamical correlation in a multi-configurational (MC) wave function theory which includes short-range (sr) dynamical correlation by density functional theory (DFT) without double counting. We demonstrate that the reliability of this approach is very good (at negligible cost), especially when considering that standard second-order multi-reference perturbation theory usually overestimates dispersion interactions.
- arXiv:1908.09447 (replaced) [pdf, other]
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Title: Symmetry-Protected Topological Triangular Weyl ComplexComments: 5 pages, 4 figuresJournal-ref: Phys. Rev. Lett. 124, 105303 (2020)Subjects: Materials Science (cond-mat.mtrl-sci); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Weyl points are often believed to appear in pairs with opposite chirality. In this work, we show by first-principles calculations and symmetry analysis that single Weyl phonons with linear dispersion and double Weyl phonons with quadratic dispersion are simultaneously present between two specific phonon branches in realistic materials with trigonal or hexagonal lattices. These phonon Weyl points are guaranteed to locate at high-symmetry points due to the screw rotational symmetry, forming a unique triangular Weyl complex. In sharp contrast to conventional Weyl systems with surface arcs terminated at the projections of a pair of Weyl points with opposite chirality, the phonon surface arcs of the unconventional triangular Weyl complex connect the projections of one double Weyl point and two single Weyl points. Importantly, the phonon surface arcs originating from the triangular Weyl complex are extremely long and span the entire surface Brillouin-zone. Furthermore, there are only nontrivial phonon surface states across the iso-frequency surface, which facilitates their detection in experiments and further applications. Our work not only offers the promising triangular phonon Weyl complex but also provides guidance for exploring triangular Weyl bosons in both phononic and photonic systems.
- arXiv:1909.00750 (replaced) [pdf, other]
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Title: Many-body chiral edge currents and sliding phases of atomic spinwaves in momentum-space latticeComments: 5 pages, 4 figrures, with Supplemental Material, accepted by Phys. Rev. LettJournal-ref: Phys. Rev. Lett. 124, 140401 (2020)Subjects: Quantum Gases (cond-mat.quant-gas); Strongly Correlated Electrons (cond-mat.str-el); Atomic Physics (physics.atom-ph)
Collective excitations (spinwaves) of long-lived atomic hyperfine states can be synthesized into a Bose-Hubbard model in momentum space. We explore many-body ground states and dynamics of a two-leg momentum-space lattice formed by two coupled hyperfine states. Essential ingredients of this setting are a staggered artificial magnetic field engineered by lasers that couple the spinwave states, and a state-dependent long-range interaction, which is induced by laser-dressing a hyperfine state to a Rydberg state. The Rydberg dressed two-body interaction gives rise to a state-dependent blockade in momentum space, and can amplify staggered flux induced anti-chiral edge currents in the many-body ground state in the presence of magnetic flux. When the Rydberg dressing is applied to both hyperfine states, exotic sliding insulating and superfluid/supersolid phases emerge. Due to the Rydberg dressed long-range interaction, spinwaves slide along a leg of the momentum-space lattice without costing energy. Our study paves a route to the quantum simulation of topological phases and exotic dynamics with interacting spinwaves of atomic hyperfine states in momentum-space lattice.
- arXiv:1909.11257 (replaced) [pdf, other]
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Title: A digital PID controller for stabilizing large electric currents to the ppm level for Feshbach resonance studiesComments: To appear in Review of Scientific InstrumentsJournal-ref: Rev. Sci. Instrum. 91, 034705 (2020)Subjects: Atomic Physics (physics.atom-ph); Quantum Gases (cond-mat.quant-gas); Instrumentation and Detectors (physics.ins-det)
Magnetic Feshbach resonances are a key tool in the field of ultracold quantum gases, but their full exploitation requires the generation of large, stable magnetic fields up to 1000 G with fractional stabilities of better than $10^{-4}$. Design considerations for electromagnets producing these fields, such as optical access and fast dynamical response, mean that electric currents in excess of 100 A are often needed to obtain the requisite field strengths. We describe a simple digital proportional-integral-derivative current controller constructed using a field-programmable gate array and off-the-shelf evaluation boards which allows for gain scheduling, enabling optimal control of current sources with non-linear actuators. Our controller can stabilize an electric current of 337.5 A to the level of $7.5\times 10^{-7}$ in an averaging time of 10 minutes and with a control bandwidth of 2 kHz.
- arXiv:1910.09641 (replaced) [pdf, other]
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Title: Prospects of forming high-spin polar molecules from ultracold atomsSubjects: Atomic Physics (physics.atom-ph); Quantum Gases (cond-mat.quant-gas)
We have investigated Feshbach resonances in collisions of high-spin atoms such as Er and Dy with closed-shell atoms such as Sr and Yb, using coupled-channel scattering and bound-state calculations. We consider both low-anisotropy and high-anisotropy limits. In both regimes we find many resonances with a wide variety of widths. The wider resonances are suitable for tuning interatomic interactions, and some of the narrower resonances are highly suitable for magnetoassociation to form high-spin molecules. These molecules might be transferred to short-range states, where they would have large magnetic moments and electric dipole moments that can be induced with very low electric fields. The results open up important prospects for a new field of ultracold high-spin polar molecules.
- arXiv:1911.06413 (replaced) [pdf, other]
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Title: Thermoelectricity modeling with cold dipole atoms in Aubry phase of optical latticeComments: 8 pages, 11 figures. Accepted for publication in Applied Sciences (MDPI)Journal-ref: Appl. Sci. 2020, 10(6), 2090Subjects: Quantum Gases (cond-mat.quant-gas)
We study analytically and numerically the thermoelectric properties of a chain of cold atoms with dipole-dipole interactions placed in an optical periodic potential. At small potential amplitudes the chain slides freely that corresponds to the Kolmogorov-Arnold-Moser phase of integrable curves of a symplectic map. Above a certain critical amplitude the chain is pinned by the lattice being in the cantori Aubry phase. We show that the Aubry phase is characterized by exceptional thermoelectric properties with the figure of merit ZT = 25 being ten times larger than the maximal value reached in material science experiments. We show that this system is well accessible for magneto-dipole cold atom experiments that opens new prospects for investigations of thermoelectricity.
- arXiv:1912.05181 (replaced) [pdf, other]
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Title: Selective tuning of spin-orbital Kondo contributions in parallel-coupled quantum dotsAuthors: Heidi Potts, Martin Leijnse, Adam Burke, Malin Nilsson, Sebastian Lehmann, Kimberly A. Dick, Claes ThelanderComments: 8 pages, 6 figuresJournal-ref: Phys. Rev. B 101, 115429 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We use co-tunneling spectroscopy to investigate spin-, orbital-, and spin-orbital Kondo transport in a strongly confined system of InAs double quantum dots (QDs) parallel-coupled to source and drain. In the one-electron transport regime, the higher symmetry spin-orbital Kondo effect manifests at orbital degeneracy and no external magnetic field. We then proceed to show that the individual Kondo contributions can be isolated and studied separately; either by orbital detuning in the case of spin-Kondo transport, or by spin splitting in the case of orbital Kondo transport. By varying the inter-dot tunnel coupling, we show that lifting of the spin degeneracy is key to confirming the presence of an orbital degeneracy, and to detecting a small orbital hybridization gap. Finally, in the two-electron regime, we show that the presence of a spin-triplet ground state results in spin-Kondo transport at zero magnetic field.
- arXiv:1912.08160 (replaced) [pdf, other]
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Title: Quantitative Theory of Triplet Pairing in the Unconventional Superconductor LaNiGa$_2$Authors: Sudeep Kumar Ghosh, Gábor Csire, Philip Whittlesea, James F. Annett, Martin Gradhand, Balázs Újfalussy, Jorge QuintanillaComments: Accepted in PRB as a rapid communicationJournal-ref: Phys. Rev. B 101, 100506 (2020)Subjects: Superconductivity (cond-mat.supr-con); Materials Science (cond-mat.mtrl-sci)
The exceptionally low-symmetry crystal structures of the time-reversal symmetry breaking superconductors LaNiC$_2$ and LaNiGa$_2$ lead to an internally-antisymmetric non-unitary triplet (INT) state as the only possibility compatible with experiments. We argue that this state has a distinct signature: a double-peak structure in the Density of States (DOS) which resolves in the spin channel in a particular way. We construct a detailed model of LaNiGa$_2$ capturing its electronic band structure and magnetic properties ab initio. The pairing mechanism is described via a single adjustable parameter. The latter is fixed by the critical temperature $T_c$ allowing parameter-free predictions. We compute the electronic specific heat and find excellent agreement with experiment. The size of the ordered moment in the superconducting state is compatible with zero-field muon spin relaxation experiments and the predicted spin-resolved DOS suggests the spin-splitting is within the reach of present experimental technology.
- arXiv:1912.11506 (replaced) [pdf, other]
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Title: Equivalence of wave function matching and Green's functions methods for quantum transport: generalized Fisher-Lee relationComments: 22 pages, 4 figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We present a proof of an exact equivalence of the two approaches that are most used in computing conductance in quantum electron and phonon transport: the wave function matching and Green's functions methods. We can obtain all the quantities defined in one method starting from those obtained in the other. This completes and illuminates the work started Ando[Ando T 1991 Phys. Rev. B 44 8017] and continued later by Komyakov et al.[Khomyakov P A, Brocks G, Karpan V, Zwierzycki M and Kelly P J 2005 Phys. Rev. B 72 035450]. The aim is to allow for solving the transport problem with whichever approach fits most the system at hand. One major corollary of the proven equivalence is our derivation of a generalized Fisher-Lee formula for resolving the transmission function into individual phonon mode contributions. As an illustration, we applied our method to a simple model to highlight its accuracy and simplicity.
- arXiv:2001.01437 (replaced) [pdf, other]
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Title: Electron glass effects in amorphous NbSi filmsComments: Submission SciPostJournal-ref: SciPost Phys. 8, 056 (2020)Subjects: Disordered Systems and Neural Networks (cond-mat.dis-nn)
We report on non equilibrium field effect in insulating amorphous NbSi thin films having different Nb contents and thicknesses. The hallmark of an electron glass, namely the logarithmic growth of a memory dip in conductance versus gate voltage curves, is observed in all the films after a cooling from room temperature to 4.2 K. A very rich phenomenology is demonstrated. While the memory dip width is found to strongly vary with the film parameters, as was also observed in amorphous indium oxide films, screening lengths and temperature dependence of the dynamics are closer to what is observed in granular Al films. Our results demonstrate that the differentiation between continuous and discontinuous systems is not relevant to understand the discrepancies reported between various systems in the electron glass features. We suggest instead that they are not of fundamental nature and stem from differences in the protocols used and in the electrical inhomogeneity length scales within each material.
- arXiv:2001.01801 (replaced) [pdf, other]
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Title: Longitudinal spin relaxation model applied to point defect qubit systemsAuthors: Viktor IvádyJournal-ref: Phys. Rev. B 101, 155203 (2020)Subjects: Quantum Physics (quant-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Controllable, partially isolated few level systems in semiconductors have recently gained multidisciplinary attention due to their widespread nanoscale sensing and quantum technology applications. Quantitative simulation of the dynamics and related applications of such systems is a challenging theoretical task that requires faithful description not only the few level systems but also their local environments. Here, we develop a method that can describe relevant relaxation processes induced by a dilute bath of nuclear and electron spins. The method utilizes an extended Lindblad equation in the framework of cluster approximation of a central spin system. We demonstrate that the proposed method can accurately describe T$_1$ time of an exemplary solid-state point defect qubit system, in particular NV center in diamond, at various magnetic fields and strain.
- arXiv:2001.02742 (replaced) [pdf, other]
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Title: Self-Consistent Quantum-Field Theory for the Characterization of Complex Random Media by Short Laser PulsesComments: published 13 pages, 7 figuresJournal-ref: Phys. Rev. Research 2, 013324 (2020)Subjects: Disordered Systems and Neural Networks (cond-mat.dis-nn); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Soft Condensed Matter (cond-mat.soft); Computational Physics (physics.comp-ph); Optics (physics.optics)
We present a quantum field theoretical method for the characterization of disordered complex media with short laser pulses in an optical coherence tomography setup (OCT). We solve this scheme of coherent transport in space and time with weighted essentially nonoscillatory methods (WENO). WENO is preferentially used for the determination of highly nonlinear and discontinuous processes including interference effects and phase transitions like Anderson localization of light. The theory determines spatiotemporal characteristics of the scattering mean free path and the transmission cross section that are directly measurable in time-of-flight (ToF) and pump-probe experiments. The results are a measure of the coherence of multiple scattering photons in passive as well as in optically soft random media. Our theoretical results of ToF are instructive in spectral regions where material characteristics such as the scattering mean free path and the diffusion coefficient are methodologically almost insensitive to gain or absorption and to higher-order nonlinear effects. Our method is applicable to OCT and other advanced spectroscopy setups including samples of strongly scattering mono- and polydisperse complex nano- and microresonators.
- arXiv:2001.04691 (replaced) [pdf, other]
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Title: Anomalous Josephson Hall effect charge and transverse spin currents in superconductor/ferromagnetic insulator/superconductor junctionsComments: 16 pages, 10 figures, Supplemental MaterialJournal-ref: Phys. Rev. B 101, 104508 (2020)Subjects: Superconductivity (cond-mat.supr-con)
Interfacial spin-orbit coupling in Josephson junctions offers an intriguing way to combine anomalous Hall and Josephson physics in a single device. We study theoretically how the superposition of both effects impacts superconductor/ferromagnetic insulator/superconductor junctions' transport properties. Transverse momentum-dependent skew tunneling of Cooper pairs through the spin-active ferromagnetic insulator interface creates sizable transverse Hall supercurrents, to which we refer as anomalous Josephson Hall effect currents. We generalize the Furusaki-Tsukada formula, which got initially established to quantify usual (tunneling) Josephson current flows, to evaluate the transverse current components and demonstrate that their amplitudes are widely adjustable by means of the spin-orbit coupling strengths or the superconducting phase difference across the junction. As a clear spectroscopic fingerprint of Josephson junctions, well-localized subgap bound states form around the interface. By analyzing the spectral properties of these states, we unravel an unambiguous correlation between spin-orbit coupling-induced asymmetries in their energies and the transverse current response, founding the currents' microscopic origin. Moreover, skew tunneling simultaneously acts like a transverse spin filter for spin-triplet Cooper pairs and complements the discussed charge current phenomena by their spin current counterparts. The junctions' universal spin-charge current cross ratios provide valuable possibilities to experimentally detect and characterize interfacial spin-orbit coupling.
- arXiv:2001.05626 (replaced) [pdf]
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Title: Hopf Bifurcation in Mean Field Explains Critical Avalanches in Excitation-Inhibition Balanced Neuronal Networks: A Mechanism for Multiscale VariabilityComments: 35 pages, 6 figures, 1 tableSubjects: Disordered Systems and Neural Networks (cond-mat.dis-nn); Neurons and Cognition (q-bio.NC)
Cortical neural circuits display highly irregular spiking in individual neurons but variably sized collective firing, oscillations and critical avalanches at the population level, all of which have functional importance for information processing. Theoretically, the balance of excitation and inhibition inputs is thought to account for spiking irregularity and critical avalanches may originate from an underlying phase transition. However, the theoretical reconciliation of these multilevel dynamic aspects remains an open question. Herein, we show that excitation-inhibition (E-I) balanced network with synaptic kinetics can maintain irregular spiking dynamics with different levels of synchrony and critical avalanches emerge near the synchronous transition point. The mechanism is unveiled by a novel mean-field theory that derives the field equations governing the network macroscopic dynamics. It reveals that the E-I balanced state of the network manifesting irregular individual spiking is characterized by a macroscopic stable state, which can be either a fixed point or a periodic motion and the transition is predicted by a Hopf bifurcation in the macroscopic field. Furthermore, these multiscale variable behaviours can be jointly observed in the spontaneous activities of mouse cortical slice in vitro, indicating universality of the theoretical prediction. Our theory unveils the mechanism that permits complex neural activities in different spatiotemporal scales to coexist and elucidates a possible origin of the criticality of neural systems. It also provides a theoretical framework for analyzing the macroscopic dynamics of E-I balanced networks and its relationship to the microscopic counterparts, which can be useful for large-scale modeling and computation of cortical dynamics.
- arXiv:2001.06313 (replaced) [pdf, other]
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Title: A library of ab initio Raman spectra for automated identification of 2D materialsComments: 17 pages, 7 figuresSubjects: Materials Science (cond-mat.mtrl-sci); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Computational Physics (physics.comp-ph)
Raman spectroscopy is frequently used to identify composition, structure and layer thickness of 2D materials. Here, we describe an efficient first-principles workflow for calculating resonant first-order Raman spectra of solids within third-order perturbation theory employing a localized atomic orbital basis set. The method is used to obtain the Raman spectra of 733 different monolayers selected from the computational 2D materials database (C2DB). We benchmark the computational scheme against available experimental data for 15 known monolayers. Furthermore, we propose an automatic procedure for identifying a material based on an input experimental Raman spectrum and illustrate it for the cases of MoS$_2$ (H-phase) and WTe$_2$ (T$^\prime$-phase). The Raman spectra of all materials at different excitation frequencies and polarization configurations are freely available from the C2DB. Our comprehensive and easily accessible library of \textit{ab initio} Raman spectra should be valuable for both theoreticians and experimentalists in the field of 2D materials
- arXiv:2002.01312 (replaced) [pdf, ps, other]
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Title: Localization anisotropy and complex geometry in two-dimensional insulatorsAuthors: Bruno MeraComments: 7 pages; closer to published versionJournal-ref: Phys. Rev. B 101, 115128 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Mathematical Physics (math-ph); Quantum Physics (quant-ph)
The localization tensor is a measure of distinguishability between insulators and metals. This tensor is related to the quantum metric tensor associated with the occupied bands in momentum space. In two dimensions and in the thermodynamic limit, it defines a flat Riemannian metric over the twist-angle space, topologically a torus, which endows this space with a complex structure, described by a complex parameter $\tau$. It is shown that the latter is a physical observable related to the anisotropy of the system. The quantity $\tau$ and the Riemannian volume of the twist-angle space provide an invariant way to parametrize the flat quantum metric obtained in the thermodynamic limit. Moreover, if by changing the couplings of the theory, the system undergoes quantum phase transitions in which the gap closes, the complex structure $\tau$ is still well defined, although the metric diverges (metallic state), and it is fixed by the form of the Hamiltonian near the gap closing points. The Riemannian volume is responsible for the divergence of the metric at the phase transition.
- arXiv:2002.07578 (replaced) [pdf, other]
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Title: String monopoles, string walls, vortex-skyrmions and nexus objects in polar distorted B-phase of $^3$HeComments: 13 pages, 7 figuresJournal-ref: PhysRevResearch.2.023263 2020Subjects: High Energy Physics - Phenomenology (hep-ph); Disordered Systems and Neural Networks (cond-mat.dis-nn); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Superconductivity (cond-mat.supr-con)
The composite cosmological objects -- Kibble-Lazarides-Shafi (KLS) walls bounded by strings and cosmic strings terminated by Nambu monopoles -- could be produced during the phase transitions in the early Universe. Recent experiments in superfluid $^3$He reproduced the formation of the KLS domain walls, which opened the new arena for the detailed study of those objects in human controlled system with different characteristic lengths. These composite defects are formed by two successive symmetry breaking phase transitions. In the first transition the strings are formed, then in the second transition the string becomes the termination line of the KLS wall. In the same manner, in the first transition monopoles are formed, and then in the second transition these monopoles become the termination points of strings. Here we show that in the vicinity of the second transition the composite defects can be described by relative homotopy groups. This is because there are two well separated length scales involved, which give rise to two different classes of the degenerate vacuum states, $R_1$ and $R_2$, and the composite objects correspond to the nontrivial elements of the group $\pi_n(R_1,R_2)$. We discuss this on example of the so-called polar distorted B phase, which is formed in the two-step phase transition in liquid $^3$He distorted by aerogel. In this system the string monopoles terminate spin vortices with even winding number, while KLS string walls terminate on half quantum vortices. In the presence of magnetic field, vortex-skyrmions are formed, and the string monopole transforms to the nexus. We also discuss the integer-valued topological invariants of those objects. Our consideration can be applied to the composite defects in other condensed matter and cosmological systems.
- arXiv:2002.12340 (replaced) [pdf, other]
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Title: Coherent Electron Optics with Ballistically Coupled Quantum Point ContactsComments: Changed author name from Piet Brouwer to Piet W. BrouwerSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
The realization of integrated quantum circuits requires precise on-chip control of charge carriers. Aiming at the coherent coupling of distant nanostructures at zero magnetic field, here we study the ballistic electron transport through two quantum point contacts (QPCs) in series in a three terminal configuration. We enhance the coupling between the QPCs by electrostatic focusing using a field effect lens. To study the emission and collection properties of QPCs in detail we combine the electrostatic focusing with magnetic deflection. Comparing our measurements with quantum mechanical and classical calculations we demonstrate how the coherent and ballistic dynamics depend on the details of the QPC confinement potentials.
- arXiv:2003.00582 (replaced) [pdf, other]
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Title: Spin-orbit interaction and spin selectivity for tunneling electron transfer in DNASubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Soft Condensed Matter (cond-mat.soft)
Electron transfer (ET) in biological molecules such as peptides and proteins consists of electrons moving between well defined localized states (donors to acceptors) through a tunneling process. Here we present an analytical model for ET by tunneling in DNA, in the presence of Spin-Orbit (SO) interaction, to produce a strong spin asymmetry with the intrinsic atomic SO strength in meV range. We obtain a Hamiltonian consistent with charge transport through $\pi$ orbitals on the DNA bases and derive the behavior of ET as a function of the injection state momentum, the spin-orbit coupling and barrier length and strength. A highly consistent scenario arises where two concomitant mechanisms for spin selection arises; spin interference and differential spin amplitude decay. High spin filtering can take place at the cost of reduced amplitude transmission assuming realistic values for the spin-orbit coupling. The spin filtering scenario is completed by addressing the spin dependent torque under the barrier, with a consistent conserved definition for the spin current.
- arXiv:2003.01923 (replaced) [pdf]
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Title: A versatile numerical approach for calculating the fracture toughness and R-curves of cellular materialsComments: 40 pages, 14 figuresJournal-ref: Journal of Mechanics and Physics of Solids (2020)Subjects: Materials Science (cond-mat.mtrl-sci)
We develop a numerical methodology for the calculation of mode-I R-curves of brittle and elastoplastic lattice materials, and unveil the impact of lattice topology, relative density and constituent material behavior on the toughening response of 2D isotropic lattices. The approach is based on finite element calculations of the J-integral on a single-edge-notch-bend (SENB) specimen, with individual bars modeled as beams having a linear elastic or a power-law elasto-plastic constitutive behavior and a maximum strain-based damage model. Results for three 2D isotropic lattice topologies (triangular, hexagonal and kagome) and two constituent materials (representative of a brittle ceramic (silicon carbide) and a strain hardening elasto-plastic metal (titanium alloy)) are presented. We extract initial fracture toughness and R-curves for all lattices and show that (i) elastic brittle triangular lattices exhibit toughening (rising R-curve), and (ii) elasto-plastic triangular lattices display significant toughening, while elasto-plastic hexagonal lattices fail in a brittle manner. We show that the difference in such failure behavior can be explained by the size of the plastic zone that grows upon crack propagation, and conclude that the nature of crack propagation in lattices (brittle vs ductile) depends both on the constituent material and the lattice architecture. While results are presented for 2D truss-lattices, the proposed approach can be easily applied to 3D truss and shell-lattices, as long as the crack tip lies within the empty space of a unit cell.
- arXiv:2003.03582 (replaced) [pdf, ps, other]
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Title: Onset of topological quantum chaos in strongly correlated electron systemsComments: 5 pages, 4 figures, supplementary material, typos correctedSubjects: Strongly Correlated Electrons (cond-mat.str-el)
We address manifestations of quantum chaos at temperatures $T$ far below the Debye temperature $T_D$ associated with the onset of classical behavior, effects that are well documented in experimental studies of strongly correlated electron systems. We attribute this unexpected phenomenon to spontaneous rearrangement of the conventional Landau state beyond a critical point at which the {\it topological} stability of this state breaks down, leading to the formation of an interaction-induced flat band adjacent to the nominal Fermi surface. We demonstrate that beyond the critical point, the quasiparticle picture of such correlated Fermi systems still holds, since the damping of single-particle excitations remains small compared with the Fermi energy $T_F=p^2_F/2m_e$. A Pitaevskii-style equation for determination of the new quasiparticle momentum distribution $n_*({\bf p})$ is derived, which provides for explanation of the linear-in-$T$ behavior of the resistivity $\rho(T)$ found experimentally. The interplay between this scenario for non-Fermi-liquid behavior of $\rho(T)$ and an alternative picture based on the notion of Planckian dissipation is discussed.
- arXiv:2003.04680 (replaced) [pdf, other]
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Title: Dzyaloshinskii-Moriya interaction in absence of spin-orbit couplingAuthors: Ramon Cardias, Anders Bergman, Attila Szilva, Yaroslav O. Kvashnin, Jonas Fransson, Angela B. Klautau, Olle Eriksson, Lars NordströmSubjects: Materials Science (cond-mat.mtrl-sci)
In contrast to conventional assumptions, we show that the Dzyaloshinskii-Moriya interaction can be of non-relativistic origin, in particular in materials with a non-collinear magnetic configuration, where non-relativistic contributions can dominate over spin-orbit effects. The weak antiferromagnetic phase of Mn$_{3}$Sn is used to illustrate these findings. Using electronic structure theory as a conceptual platform, all relevant exchange interactions are derived for a general, non-collinear magnetic state. It is demonstrated that non-collinearity influences all three types of exchange interaction and that physically distinct mechanisms, which connect to electron- and spin-density and currents, may be used as a general way to analyze and understand magnetic interactions of the solid state.
- arXiv:2003.05804 (replaced) [pdf, other]
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Title: The Ising model in a light-induced quantized transverse fieldComments: 17 pages, 6 figuresJournal-ref: Phys. Rev. Research 2, 023131 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el)
We investigate the influence of light-matter interactions on correlated quantum matter by studying the paradigmatic Ising model subject to a quantum Rabi coupling. This type of coupling to a confined, spatially delocalized bosonic light mode, such as provided by an optical resonator, resembles a quantized transverse magnetic field of tunable strength. As a consequence, the symmetry-broken magnetic state breaks down for strong enough light-mater interactions to a paramagnetic state. The non-local character of the bosonic mode can change the quantum phase transition in a drastic manner, which we analyze quantitatively for the simplest case of a chain geometry (Dicke-Ising chain). The results show a direct transition between a magnetically ordered phase with zero photon density and a magnetically polarized phase with lasing behaviour of the light. Our predictions are equally valid for the dual quantized Ising chain in a conventional transverse magnetic field.
- arXiv:2003.06558 (replaced) [pdf, ps, other]
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Title: Electro-osmotic properties of porous permeable filmsSubjects: Soft Condensed Matter (cond-mat.soft); Chemical Physics (physics.chem-ph)
Permeable porous coatings on a flat solid support significantly impact its electrostatic and electrokinetic properties. Existing work has focused on simplified cases, such as weakly charged and/or thick porous films, with limited theoretical guidance. Here, we consider the general case of coatings of any given volume charge density and obtain analytic formulas for electrostatic potential profiles, valid for any film thickness and salt concentration. They allow us to calculate analytically the difference between potentials at solid support and at interface with an outer electrolyte, that is the key parameter ascertaining the functionality of permeable coatings. Our analysis provides a framework for interpreting and predicting specific for porous films super-properties, from an enhanced ion absorption to a giant amplification of electro-osmotic flows. The results are relevant for hydrogel and zeolite coatings, porous carbon and ion-exchange resins, polyelectrolyte brushes, and more.
- arXiv:2003.06601 (replaced) [pdf, other]
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Title: Lattice protein design using Bayesian learningComments: 9 pages, 8 figuresSubjects: Biological Physics (physics.bio-ph); Statistical Mechanics (cond-mat.stat-mech); Machine Learning (cs.LG); Chemical Physics (physics.chem-ph)
A novel protein design method using Bayesian learning is proposed in this work. We consider a posterior probability of amino acid sequences by taking into account water and assuming a prior of sequences. For some instances of a target conformation of a two-dimensional (2D) lattice Hydrophobic-Polar (HP) model, our method successfully finds an amino acid sequence for which the target conformation has a unique ground state. However, the performance was not as good for 3D lattice HP models compared with 2D models. Furthermore, we find a strong linearity between the chemical potential of water and the number of surface residues, thereby revealing the relationship between protein structure and the effect of water molecules. The advantage of our method is that it greatly reduces computation time, because it does not require long calculations for the partition function corresponding to an exhaustive conformational search. As our method uses a general form of Bayesian learning and statistical mechanics and is not limited to lattice HP proteins, the results presented here elucidate some heuristics used successfully in previous protein design methods.
- arXiv:2003.06900 (replaced) [pdf, other]
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Title: Vacancy diffusion in multi-principal element alloys: the role of chemical disorder in the ordered latticeSubjects: Materials Science (cond-mat.mtrl-sci)
Many of the purported virtues of Multi-Principal Element Alloys (MPEAs), such as corrosion, high-temperature oxidation and irradiation resistance, are highly sensitive to vacancy diffusivity. Similarly, solute interdiffusion is governed by vacancy diffusion -- it is often unclear whether MPEAs are truly stable, or effectively stabilized by slow interdiffusion. The considerable composition space afforded to these alloys makes optimizing for desired properties a daunting task; theoretical and computational tools are necessary to guide alloy development. For diffusion, such tools depend on both a knowledge of the vacancy migration barriers within a given alloy and an understanding of how these barriers influence vacancy diffusivity. We present a generalized theory of vacancy diffusion in rugged energy landscapes, paired with Kinetic Monte Carlo simulations of MPEA vacancy diffusion. The barrier energy statistics are informed by nudged elastic band calculations in the equiatomic CoNiCrFeMn alloy. Theory and simulations show that vacancy diffusion in solid-solution MPEAs is not necessarily sluggish, but can potentially be tuned, and that trap models are an insufficient explanation for sluggish diffusion in the CoNiCrFeMn HEA. These results also show that any model that endeavors to faithfully represent diffusion-related phenomena must account for the full nature of the energy landscape, not just the migration barriers.
- arXiv:2003.07213 (replaced) [pdf]
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Title: Observation of a three-dimensional fractional Hall response in HfTe5Authors: S. Galeski, X. Zhao, R. Wawrzyńczak, T. Meng, T. Förster, S. Honnali, N. Lamba, T. Ehmcke, A. Markou, W. Zhu, J. Wosnitza, C. Felser, G. F. Chen, J. GoothComments: 35 pages with 17 figuresSubjects: Strongly Correlated Electrons (cond-mat.str-el); Materials Science (cond-mat.mtrl-sci)
Interacting electrons in two dimensions can bind magnetic flux lines to form composite quasiparticles with fractional electric charge, manifesting themselves in the fractional quantum Hall effect (FQHE). Although the FQHE has also been predicted to occur in three dimensions, it has not yet been experimentally observed. Here, we report the observation of fractional plateaus in the Hall conductivity of the bulk semimetal HfTe5 at magnetic fields beyond the quantum limit. The plateaus are accompanied by Shubnikov-de Haas minima of the longitudinal electrical resistivity. The height of the Hall plateaus is given by twice the Fermi wave vector in the direction of the applied magnetic field and scales with integer and particular fractional multiples of the conductance quantum. Our findings are consistent with strong electron-electron interactions, stabilizing a fractionalized variant of the Hall effect in three dimensions.
- arXiv:cond-mat/0107612 (replaced) [pdf, other]
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Title: Extremely Dilute Modular Neuronal Networks: Neocortical Memory Retrieval DynamicsAuthors: Carlo Fulvi MariComments: 23 pages, 8 figures (PDF), pdflatex. Pre-peer-review version (for copyright reasons). The more readable post-peer-review author's version is available on the author's personal webpage, which is accessible from orcid.org and Google ScholarSubjects: Disordered Systems and Neural Networks (cond-mat.dis-nn); Biological Physics (physics.bio-ph); Quantitative Biology (q-bio); Neurons and Cognition (q-bio.NC)
A model of the columnar functional organization of neocortical association areas is studied. The neuronal network is composed of many Hebbian autoassociators, or modules, each of which interacts with a relatively small number of the others. Every module encodes and stores a number of elementary percepts, or features. Memory items, or patterns, are peculiar combinations of features sparsely distributed over the multi-modular network. Any feature stored in any module can be involved in several of the stored patterns; feature-sharing is in fact source of local ambiguities and, consequently, a potential cause of erroneous memory retrieval activity spreading through the model network.
The memory retrieval dynamics of the large multi-modular autoassociator is investigated by means of quantitative analysis and numerical simulations. An oscillatory retrieval process is found to be very efficient in overcoming feature-sharing drawbacks; it requires a mechanism that modulates the robustness of local attractors to noise, and neuronal activity sparseness such that quiescent and active modules are about equally noisy. Correlated activation of interconnected modules and extramodular neuronal contacts more effective than the intramodular ones seem to be general requirements in order to efficiently achieve satisfactory quality of memory retrieval. It is also shown that, even in ideal conditions, some spots of the network cannot be reached by retrieval activity spread. The locations of these activity isles depend on the pattern to retrieve and on the cue, while their extension only depends on architecture of the graph and statistics of the stored patterns. The existence of these isles determines an upper-bound to retrieval quality that does not depend on the specific retrieval dynamics adopted, nor on whether feature-sharing is permitted. The oscillatory retrieval process nearly saturates this bound. - arXiv:1311.7263 (replaced) [pdf, other]
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Title: Anisotropic optical conductivity and electron-hole asymmetry in doped monolayer graphene in the presence of the Rashba couplingJournal-ref: Physica E (2015) 70:28Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
In this study, the Optical conductivity of substitutionary doped graphene is investigated in presence of the Rashba spin orbit coupling (RSOC). Calculations have been performed within the coherent potential approximation (CPA) beyond the Dirac cone approximation. Results of the current study demonstrate that the optical conductivity is increased by increasing the RSOC strength. Meanwhile it was observed that the anisotropy of the band energy results in a considerable anisotropic optical conductivity (AOC) in monolayer graphene. The sign and magnitude of this anisotropic conductivity was shown to be controlled by the external field frequency. It was also shown that the Rashba interaction results in electron-hole asymmetry in monolayer graphene.
- arXiv:1512.00633 (replaced) [pdf, other]
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Title: Dramatic pressure-driven enhancement of bulk skyrmion stabilityAuthors: I. Levatić, P. Popčević, V. Šurija, A. Kruchkov, H. Berger, A. Magrez, J. S. White, H. M. Rønnow, I. ŽivkovićComments: submitted to Scientific ReportsJournal-ref: Scientific Reports 6, 21347 (2016)Subjects: Strongly Correlated Electrons (cond-mat.str-el); Materials Science (cond-mat.mtrl-sci)
The recent discovery of magnetic skyrmion lattices initiated a surge of interest in the scientific community. Several novel phenomena have been shown to emerge from the interaction of conducting electrons with the skyrmion lattice, such as a topological Hall-effect and a spin-transfer torque at ultra-low current densities. In the insulating compound Cu2OSeO3, magneto-electric coupling enables control of the skyrmion lattice via electric fields, promising a dissipation-less route towards novel spintronic devices. One of the outstanding fundamental issues is related to the thermodynamic stability of the skyrmion lattice. To date, the skyrmion lattice in bulk materials has been found only in a narrow temperature region just below the order-disorder transition. If this narrow stability is unavoidable, it would severely limit applications. Here we present the discovery that applying just moderate pressure on Cu2OSeO3 substantially increases the absolute size of the skyrmion pocket. This insight demonstrates directly that tuning the electronic structure can lead to a significant enhancement of the skyrmion lattice stability. We interpret the discovery by extending the previously employed Ginzburg-Landau approach and conclude that change in the anisotropy is the main driver for control of the size of the skyrmion pocket. This realization provides an important guide for tuning the properties of future skyrmion hosting materials.
- arXiv:1710.10221 (replaced) [pdf]
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Title: Unusual behavior of cuprates explained by heterogeneous charge localizationJournal-ref: Science Advances 5, eaau4538 (2019)Subjects: Superconductivity (cond-mat.supr-con); Strongly Correlated Electrons (cond-mat.str-el)
The cuprate high-temperature superconductors are among the most intensively studied materials, yet essential questions regarding their principal phases and the transitions between them remain unanswered. Generally thought of as doped charge-transfer insulators, these complex lamellar oxides exhibit pseudogap, strange-metal, superconducting and Fermi-liquid behaviour with increasing hole-dopant concentration. Here we propose a simple inhomogeneous Mott-like (de)localization model wherein exactly one hole per copper-oxygen unit is gradually delocalized with increasing doping and temperature. The model is percolative in nature, with parameters that are experimentally constrained. It comprehensively captures pivotal unconventional experimental results, including the temperature and doping dependence of the pseudogap phenomenon, the strange-metal linear temperature dependence of the planar resistivity, and the doping dependence of the superfluid density. The success and simplicity of our model greatly demystify the cuprate phase diagram and point to a local superconducting pairing mechanism involving the (de)localized hole.
- arXiv:1711.09963 (replaced) [pdf, ps, other]
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Title: Systolic aspects of black hole entropyAuthors: Nikolaos KalogeropoulosComments: 20 pages. No figures. LaTeX2e. This version: change of the author's affiliation. Other minor changes. To be published in a Special Issue of "Axioms" on "Theory and Mathematical Aspects of Black Holes"Journal-ref: Axioms 9(1), 30 (2020)Subjects: General Relativity and Quantum Cosmology (gr-qc); Statistical Mechanics (cond-mat.stat-mech); High Energy Physics - Theory (hep-th); Mathematical Physics (math-ph)
We attempt to provide a mesoscopic treatment of the origin of black hole entropy in (3+1)-dimensional spacetimes. We ascribe this entropy to the non-trivial topology of the space-like sections $\Sigma$ of the horizon. This is not forbidden by topological censorship, since all the known energy inequalities needed to prove the spherical topology of $\Sigma$ are violated in quantum theory. We choose the systoles of $\Sigma$ to encode its complexity, which gives rise to the black hole entropy. We present hand-waving reasons why the entropy of the black hole can be considered as a function of the volume entropy of $\Sigma$. We focus on the limiting case of $\Sigma$ having a large genus.
- arXiv:1811.12840 (replaced) [pdf, other]
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Title: Experimental measurement of the quantum geometric tensor using coupled qubits in diamondAuthors: Min Yu, Pengcheng Yang, Musang Gong, Qingyun Cao, Qiuyu Lu, Haibin Liu, Martin B. Plenio, Fedor Jelezko, Tomoki Ozawa, Nathan Goldman, Shaoliang Zhang, Jianming CaiJournal-ref: National Science Review 7: 254-260, 2020Subjects: Quantum Physics (quant-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Geometry and topology are fundamental concepts, which underlie a wide range of fascinating physical phenomena such as topological states of matter and topological defects. In quantum mechanics, the geometry of quantum states is fully captured by the quantum geometric tensor. Using a qubit formed by an NV center in diamond, we perform the first experimental measurement of the complete quantum geometric tensor. Our approach builds on a strong connection between coherent Rabi oscillations upon parametric modulations and the quantum geometry of the underlying states. We then apply our method to a system of two interacting qubits, by exploiting the coupling between the NV center spin and a neighboring $^{13}$C nuclear spin. Our results establish coherent dynamical responses as a versatile probe for quantum geometry, and they pave the way for the detection of novel topological phenomena in solid state.
- arXiv:1903.05446 (replaced) [pdf]
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Title: Unidirectional single-photon emission from germanium-vacancy zero-phonon lines: Deterministic emitter-waveguide interfacing at plasmonic hot spotsAuthors: Hamidreza Siampour, Ou Wang, Vladimir A. Zenin, Sergejs Boroviks, Petr Siyushev, Yuanqing Yang, Valery A. Davydov, Liudmila F. Kulikova, Viatcheslav N. Agafonov, Alexander Kubanek, N. Asger Mortensen, Fedor Jelezko, Sergey I. BozhevolnyiJournal-ref: Nanophotonics 9, 953 (2020)Subjects: Applied Physics (physics.app-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Optics (physics.optics)
Striving for nanometer-sized solid-state single-photon sources, we investigate atom-like quantum emitters based on single germanium vacancy (GeV) centers isolated in crystalline nanodiamonds (NDs). Cryogenic characterization indicated symmetry-protected and bright (> 10^6 counts/s with off-resonance excitation) zero-phonon optical transitions with up to 6-fold enhancement in energy splitting of their ground states as compared to that found for GeV centers in bulk diamonds (i.e., up to 870 GHz in highly strained NDs vs 150 GHz in bulk). Utilizing lithographic alignment techniques, we demonstrate an integrated nanophotonic platform for deterministic interfacing plasmonic waveguides with isolated GeV centers in NDs that enables 10-fold enhancement of single-photon decay rates along with the emission direction control by judiciously designing and positioning a Bragg reflector. This approach allows one to realize the unidirectional emission from single-photon dipolar sources introducing a novel method that is alternative to the propagation-direction-dependent techniques based on chiral interactions or topological protection. The developed plasmon-based nanophotonic platform opens thereby new perspectives for quantum nanophotonics in general and for realizing entanglement between single photons and spin qubits, in particular.
- arXiv:1903.07919 (replaced) [pdf, other]
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Title: Topological defects produce exotic mechanics in complex metamaterialsComments: Main text of 8 pages including 4 figures, supplementary information of 8 pages including 7 figuresJournal-ref: Nature Physics 16, 307 (2020)Subjects: Soft Condensed Matter (cond-mat.soft); Materials Science (cond-mat.mtrl-sci)
Defects, and in particular topological defects, are architectural motifs that play a crucial role in natural materials. Here we provide a systematic strategy to introduce such defects in mechanical metamaterials. We first present metamaterials that are a mechanical analogue of spin systems with tunable ferromagnetic and antiferromagnetic interactions, then design an exponential number of frustration-free metamaterials, and finally introduce topological defects by rotating a string of building blocks in these metamaterials. We uncover the distinct mechanical signature of topological defects by experiments and simulations, and leverage this to design complex metamaterials in which we can steer deformations and stresses towards parts of the system. Our work presents a new avenue to systematically include spatial complexity, frustration, and topology in mechanical metamaterials.
- arXiv:1904.10999 (replaced) [pdf, other]
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Title: Observation of a gel of quantum vortices in a superconductor at very low magnetic fieldsAuthors: José Benito Llorens, Lior Embon, Alexandre Correa, Jesés David González, Edwin Herrera, Isabel Guillamón, Roberto F. Luccas, Jon Azpeitia, Federico J. Mompeán, Mar García-Hernández, Carmen Munuera, Jazmín Aragón Sánchez, Yanina Fasano, Milorad V. Milosevic, Hermann Suderow, Yonathan AnahoryJournal-ref: Phys. Rev. Research 2, 013329 (2020)Subjects: Superconductivity (cond-mat.supr-con); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Soft Condensed Matter (cond-mat.soft); Strongly Correlated Electrons (cond-mat.str-el)
A gel consists of a network of particles or molecules formed for example using the sol-gel process, by which a solution transforms into a porous solid. Particles or molecules in a gel are mainly organized on a scaffold that makes up a porous system. Quantized vortices in type II superconductors mostly form spatially homogeneous ordered or amorphous solids. Here we present high-resolution imaging of the vortex lattice displaying dense vortex clusters separated by sparse or entirely vortex-free regions in $\beta$-Bi$_2$Pd superconductor. We find that the intervortex distance diverges upon decreasing the magnetic field and that vortex lattice images follow a multifractal behavior. These properties, characteristic of gels, establish the presence of a novel vortex distribution, distinctly different from the well-studied disordered and glassy phases observed in high-temperature and conventional superconductors. The observed behavior is caused by a scaffold of one-dimensional structural defects with enhanced stress close to the defects. The vortex gel might often occur in type-II superconductors at low magnetic fields. Such vortex distributions should allow to considerably simplify control over vortex positions and manipulation of quantum vortex states.
- arXiv:1904.11425 (replaced) [pdf]
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Title: 1,000-Fold Enhancement of Light-Induced Magnetism in Plasmonic Au NanoparticlesComments: 13 pages, 5 figures, supplementary information 6 pages. SubmittedSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Strategies for ultrafast optical control of magnetism have been a topic of intense research for several decades because of the potential impact in technologies such as magnetic memory, spintronics, and quantum computation, as well as the opportunities for non-linear optical control and modulation in applications such as optical isolation and non-reciprocity. Here we report the first experimental quantification of optically induced magnetization in plasmonic Au nanoparticles due to the inverse Faraday effect (IFE). The induced magnetic moment in nanoparticles is found to be ~1,000x larger than that observed in bulk Au, and ~20x larger than the magnetic moment from optimized magnetic nanoparticle colloids such as magnetite. Furthermore, the magnetization and demagnetization kinetics are instantaneous within the sub-picosecond time resolution of our study, supporting a mechanism of coherent transfer of angular momentum from the circularly polarized excitation to the orbital angular momentum of the electron gas.
- arXiv:1905.01672 (replaced) [pdf, ps, other]
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Title: Toward a relative q-entropyAuthors: Nikolaos KalogeropoulosComments: Minor changes in this version. 23 pages. No figures. LaTeX2e. To be published in Physica AJournal-ref: Physica A 545, 123270 (2020)Subjects: Statistical Mechanics (cond-mat.stat-mech); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Theory (hep-th); Mathematical Physics (math-ph)
We address the question and related controversy of the formulation of the $q$-entropy, and its relative entropy counterpart, for models described by continuous (non-discrete) sets of variables. We notice that an $L_p$ normalized functional proposed by Lutwak-Yang-Zhang (LYZ), which is essentially a variation of a properly normalized relative R\'{e}nyi entropy up to a logarithm, has extremal properties that make it an attractive candidate which can be used to construct such a relative $q$-entropy. We comment on the extremizing probability distributions of this LYZ functional, its relation to the escort distributions, a generalized Fisher information and the corresponding Cram\'{e}r-Rao inequality. We point out potential physical implications of the LYZ entropic functional and of its extremal distributions.
- arXiv:1905.09912 (replaced) [pdf, other]
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Title: Stochastic Yield Catastrophes and Robustness in Self-AssemblySubjects: Biological Physics (physics.bio-ph); Soft Condensed Matter (cond-mat.soft); Subcellular Processes (q-bio.SC)
A guiding principle in self-assembly is that, for high production yield, nucleation of structures must be significantly slower than their growth. However, details of the mechanism that impedes nucleation are broadly considered irrelevant. Here, we analyze self-assembly into finite-sized target structures employing mathematical modeling. We investigate two key scenarios to delay nucleation: (i) by introducing a slow activation step for the assembling constituents and, (ii) by decreasing the dimerization rate. These scenarios have widely different characteristics. While the dimerization scenario exhibits robust behavior, the activation scenario is highly sensitive to demographic fluctuations. These demographic fluctuations ultimately disfavor growth compared to nucleation and can suppress yield completely. The occurrence of this stochastic yield catastrophe does not depend on model details but is generic as soon as number fluctuations between constituents are taken into account. On a broader perspective, our results reveal that stochasticity is an important limiting factor for self-assembly and that the specific implementation of the nucleation process plays a significant role in determining the yield.
- arXiv:1907.07864 (replaced) [pdf, other]
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Title: Resonant soft x-ray scattering from stripe-ordered La$_{2-x}$Ba$_x$CuO$_4$ detected by a transition edge sensor array detectorAuthors: Y. I. Joe, Y. Fang, S. Lee, S. X. L. Sun, G. A. de la Peña, W. B. Doriese, K. M. Morgan, J. W. Fowler, L. R. Vale, F. Rodolakis, J. L. McChesney, J. N. Ullom, D. S. Swetz, P. AbbamonteComments: 10 pages, 6 figuresJournal-ref: Phys. Rev. Applied 13, 034026 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el); Instrumentation and Detectors (physics.ins-det); Quantum Physics (quant-ph)
Resonant soft x-ray scattering (RSXS) is a leading probe of valence band order in materials best known for detecting charge density wave order in the copper-oxide superconductors. One of the biggest limitations on the RSXS technique is the presence of a severe fluorescence background which, like the RSXS cross section itself, is enhanced under resonant conditions. This background prevents the study of weak signals such as diffuse scattering from glassy or fluctuating order that is spread widely over momentum space. Recent advances in superconducting transition edge sensor (TES) detectors have led to major improvements in energy resolution and detection efficiency in the soft x-ray range. Here, we perform a RSXS study of stripe-ordered La$_{2-x}$Ba$_x$CuO$_4$ at the Cu $L_{3/2}$ edge (932.2 eV) using a TES detector with 1.5 eV resolution, to evaluate its utility for mitigating the fluorescence background problem. We find that, for suitable degree of detuning from the resonance, the TES rejects the fluorescence background, leading to a 5 to 10 times improvement in the statistical quality of the data compared to an equivalent, energy-integrated measurement. We conclude that a TES presents a promising approach to reducing background in RSXS studies and may lead to new discoveries in materials exhibiting valence band order that is fluctuating or glassy.
- arXiv:1907.08929 (replaced) [pdf]
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Title: Elastic interactions of Fe adatoms on Cu(111) at the mesoscaleAuthors: Wolfgang KappusComments: 12 pages, 3 figures, review updateJournal-ref: Surf. Sci. 695, 121472 (2020)Subjects: Materials Science (cond-mat.mtrl-sci); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
An extended elastic eigenvector approach had earlier been developed to interpret ab-initio calculations of adatom interactions. It shows oscillating interactions as well as trio- and quarto (multisite) terms within clusters. It is now applied to the interaction of Fe adatoms on Cu(111). The extended approach differs from previous calculations by using a sharp cutoff - generating oscillating interactions - and by taking into account interacting dimers - generating strong anisotropies and multisite terms. Additional weak anisotropy stems from the substrate and from the surface Brillouin zone shape. This approach has 3 free parameters which have been fitted to first principles interactions of Fe adatoms on Cu(111). Elastic adatom pair interactions and dimer-dimer interactions at mesoscale separations show a reasonable good fit to the first principles interactions. At smaller separations elastic interaction values remain questionable. To enable a comparison with future first principle calculations also dimer-monomer interactions are shown. Some conclusions on initial adatom formation and diffusion are proposed and open questions are formulated.
- arXiv:1909.02112 (replaced) [pdf, other]
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Title: Graphenylene-1 Membrane: An Excellent Candidate for Hydrogen Purification and Helium SeparationSubjects: Materials Science (cond-mat.mtrl-sci); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Chemical Physics (physics.chem-ph); Computational Physics (physics.comp-ph)
In this study, we use the density functional theory (DFT) calculations and the molecular dynamics (MD) simulations to investigate the performance of graphenylene--1 membrane for hydrogen ($H_2$) purification and helium ($He$) separation. The stability of this membrane is confirmed by calculating its cohesive energy. Our results show that a surmountable energy barrier for $H_2$ (0.384 eV) and $He$ (0.178 eV) molecules passing through graphenylene-1 membrane. At room temperature, the selectivity of $H_2$/$CO_2$, $H_2$/$N_2$, $H_2$/$CO$ and $H_2$/$CH_4$ are obtained as $3 \times 10^{27}$, $2 \times 10^{18}$, $1 \times 10^{17}$ and $6 \times 10^{46}$, respectively. Furthermore, we demonstrate that graphenylene-1 membrane exhibits the permeance of $H_2$ and He molecules are much higher than the value of them in the current industrial applications specially at temperatures above 300 K and 150 K, respectively. We further performed MD simulations to confirm the results of DFT calculations. All these results show that graphenylene-1 monolayer membrane is an excellent candidate for $H_2$ purification and He separation.
- arXiv:1909.03378 (replaced) [pdf]
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Title: Memories in the Photoluminescence Intermittency of Single Cesium Lead Bromide NanocrystalsAuthors: Lei Hou, Chen Zhao, Xi Yuan, Jialong Zhao, Franziska Krieg, Philippe Tamarat, Maksym V. Kovalenko, Chunlei Guo, Brahim LounisJournal-ref: Nanoscale (2020)Subjects: Applied Physics (physics.app-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Optics (physics.optics)
Single cesium lead bromide (CsPbBr3) nanocrystals show strong photoluminescence blinking, with on- and off- dwelling times following power-law distributions. We investigate the memory effect in the photoluminescence blinking of single CsPbBr3 nanocrystals and find positive correlations for successive on-times and successive off-times. This memory effect is not sensitive to the nature of the surface capping ligand and the embedding polymer. These observations suggest that photoluminescence intermittency and its memory are mainly controlled by intrinsic traps in the nanocrystals. These findings will help optimizing light-emitting devices based on inorganic perovskite nanocrystals.
- arXiv:1909.13515 (replaced) [pdf]
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Title: Visualization of local magnetic moments emerging from impurities in the Hund's metal states of FeSeComments: 35 pages including main text and supplemental materialJournal-ref: Phys. Rev. Lett. 124, 117001 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el); Superconductivity (cond-mat.supr-con)
Understanding the origin of the magnetism of high temperature superconductors is crucial for establishing their unconventional pairing mechanism. Recently, theory predicts that FeSe is close to a magnetic quantum critical point, and thus weak perturbations such as impurities could induce local magnetic moments. To elucidate such quantum instability, we have employed scanning tunneling microscopy and spectroscopy. In particular, we have grown FeSe film on superconducting Pb(111) using molecular beam epitaxy and investigated magnetic excitation caused by impurities in the proximity-induced superconducting gap of FeSe. Our study provides a deep insight into the origin of the magnetic ordering of FeSe by showing the way local magnetic moments develop in response to impurities near the magnetic quantum critical point.
- arXiv:1911.07188 (replaced) [pdf, other]
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Title: On entanglement hamiltonians of an interval in massless harmonic chainsComments: 41 pages, 18 figuresJournal-ref: J. Stat. Mech. (2020) 033102Subjects: Statistical Mechanics (cond-mat.stat-mech); High Energy Physics - Theory (hep-th)
We study the continuum limit of the entanglement hamiltonians of a block of consecutive sites in massless harmonic chains. This block is either in the chain on the infinite line or at the beginning of a chain on the semi-infinite line with Dirichlet boundary conditions imposed at its origin. The entanglement hamiltonians of the interval predicted by Conformal Field Theory for the massless scalar field are obtained in the continuum limit. We also study the corresponding entanglement spectra and the numerical results for the ratios of the gaps are compatible with the operator content of the Boundary Conformal Field Theory of a massless scalar field with Neumann boundary conditions imposed along the boundaries introduced around the entangling points by the regularisation procedure.
- arXiv:1911.08035 (replaced) [pdf, other]
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Title: Axion-Field-Enabled Nonreciprocal Thermal Radiation in Weyl SemimetalsComments: 6 pages, 3 figuresJournal-ref: Nano Letters 2020 20 (3), 1923-1927Subjects: Optics (physics.optics); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Objects around us constantly emit and absorb thermal radiation. The emission and absorption processes are governed by two fundamental radiative properties: emissivity and absorptivity.For reciprocal systems, the emissivity and absorptivity are restricted to be equal by Kirchhoff's law of thermal radiation. This restriction limits the degree of freedom to control thermal radiation and contributes to an intrinsic loss mechanism in photonic energy harvesting systems such assolar cells. Existing approaches to violate Kirchhoff's law typically utilize conventional magneto-optical effects in the presence of an external magnetic field. However, these approaches require either a strong magnetic field (~3T), or narrow-band resonances under a moderate magnetic field (~0.3T), because the non-reciprocity in conventional magneto-optical effects isusually weak in the thermal wavelength range. Here, we show that the axion electrodynamics in magnetic Weyl semimetals can be used to construct strongly nonreciprocal thermal emitters that near completely violate Kirchhoff's law over broad angular and frequency ranges, without requiring any external magnetic field. The non-reciprocity moreover is strongly temperature tunable, opening new possibilities for active non-reciprocal devices in controlling thermal radiation.
- arXiv:2001.00300 (replaced) [pdf]
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Title: Origin of Strong Two-Magnon Scattering in Heavy Metal/Ferromagnet/Oxide HeterostructuresJournal-ref: Phys. Rev. Applied 13, 034038 (2020)Subjects: Materials Science (cond-mat.mtrl-sci); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We experimentally investigate the origin of the two-magnon scattering (TMS) in heavy-metal (HM)/ferromagnet (FM)/oxide heterostructures (FM = Co, Ni81Fe19, or Fe60Co20B20) by varying the materials located above and below the FM layers. We show that strong TMS in HM/FM/oxide systems arises primarily at the HM/FM interface and increases with the strength of interfacial spin-orbit coupling and magnetic roughness at this interface. TMS at the FM/oxide interface is relatively weak, even in systems where spin-orbit coupling at this interface generates strong interfacial magnetic anisotropy. We also suggest that the spin-current-induced excitation of non-uniform short-wavelength magnon at the HM/FM interface may function as a mechanism of spin memory loss for the spin-orbit torque exerted on the uniform mode.
- arXiv:2002.04159 (replaced) [pdf, other]
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Title: Observation of an antiferromagnetic quantum critical point in high-purity LaNiO$_3$Authors: Changjiang Liu, Vincent F. C. Humbert, Terence Bretz-Sullivan, Gensheng Wang, Deshun Hong, Friederike Wrobel, Jianjie Zhang, Jason D. Hoffman, John E. Pearson, J Samuel Jiang, Clarence Chang, Alexey Suslov, Nadya Mason, M. R. Norman, Anand BhattacharyaJournal-ref: Nat. Commun. 11, 1402 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el); Materials Science (cond-mat.mtrl-sci)
Amongst the rare-earth perovskite nickelates, LaNiO$_3$ (LNO) is an exception. While the former have insulating and antiferromagnetic ground states, LNO remains metallic and non-magnetic down to the lowest temperatures. It is believed that LNO is a strange metal, on the verge of an antiferromagnetic instability. Our work suggests that LNO is a quantum critical metal, close to an antiferromagnetic quantum critical point (QCP). The QCP behavior in LNO is manifested in epitaxial thin films with unprecedented high purities. We find that the temperature and magnetic field dependences of the resistivity of LNO at low temperatures are consistent with scatterings of charge carriers from weak disorder and quantum fluctuations of an antiferromagnetic nature. Furthermore, we find that the introduction of a small concentration of magnetic impurities qualitatively changes the magnetotransport properties of LNO, resembling that found in some heavy-fermion Kondo lattice systems in the vicinity of an antiferromagnetic QCP.
- arXiv:2002.06614 (replaced) [pdf, other]
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Title: Plasmon-phonon-polaritons in encapsulated phosphoreneComments: 16 pages, 11 figures, This is a post-peer-review, pre-copyedit version of an article which will be published in PlasmonicsSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We consider a system consists of a doped monolayer phosphorene embedded between two hexagonal Boron Nitride (hBN) slabs along the heterostructure direction. The wavevector azimuthal angle dependence of the plasmon-polariton and plasmon-phonon-polariton modes of the hybrid system are calculated based on the random phase approximation at finite temperature. The collective modes illustrate strong anisotropy and strong coupling with phonon modes of the polar media and furthermore, the Landau damping occurs due to the intraband processes when plasmon enters intraband electron-hole continuum. Our numerical results show that the plasmon mode is highly confined to the surface along the zigzag direction. Owing to the strong electron-phonon interaction, the phonon dispersions in the Reststrahlen bands are also angle-dependent. These results are also in agreement with those of the semiclassical model obtained in our calculations.
- arXiv:2003.03336 (replaced) [pdf]
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Title: Raman spectroscopy of GaSe and InSe post-transition metal chalcogenides layersAuthors: Maciej R. Molas, Anastasia V. Tyurnina, Viktor Zólyomi, Anna K. Ott, Daniel J. Terry, Matthew J. Hamer, Celal Yelgel, Adam Babiński, Albert G. Nasibulin, Andrea C. Ferrari, Vladimir I. Fal'ko, Roman GorbachevComments: 6 pages, 5 figuresJournal-ref: Faraday Discussions 2020Subjects: Materials Science (cond-mat.mtrl-sci); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
III-VI post-transition metal chalcogenides (InSe and GaSe) are a new class of layered semiconductors, which feature a strong variation of size and type of their band gaps as a function of number of layers (N). Here, we investigate exfoliated layers of InSe and GaSe ranging from bulk crystals down to monolayer, encapsulated in hexagonal boron nitride, using Raman spectroscopy. We present the N-dependence of both intralayer vibrations within each atomic layer, as well as of the interlayer shear and layer breathing modes. A linear chain model can be used to describe the evolution of the peak positions as a function of N, consistent with first principles calculations.
Crosses
- arXiv:2003.06087 (cross-list from quant-ph) [pdf, other]
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Title: Protecting Spin Coherence in a Tunable Heisenberg ModelAuthors: Emily J. Davis, Avikar Periwal, Eric S. Cooper, Gregory Bentsen, Simon J. Evered, Katherine Van Kirk, Monika H. Schleier-SmithSubjects: Quantum Physics (quant-ph); Quantum Gases (cond-mat.quant-gas)
Using an ensemble of atoms in an optical cavity, we engineer a family of nonlocal Heisenberg Hamiltonians with continuously tunable anisotropy of the spin-spin couplings. We thus gain access to a rich phase diagram, including a paramagnetic-to-ferromagnetic Ising phase transition that manifests as a diverging magnetic susceptibility at the critical point. The susceptibility displays a symmetry between Ising interactions and XY (spin-exchange) interactions of the opposite sign, which is indicative of the spatially extended atomic system behaving as a single collective spin. Images of the magnetization dynamics show that spin-exchange interactions protect the coherence of the collective spin, even against inhomogeneous fields that completely dephase the non-interacting and Ising systems. Our results underscore prospects for harnessing spin-exchange interactions to enhance the robustness of spin squeezing protocols.
- arXiv:2003.06837 (cross-list from cond-mat.mes-hall) [pdf, other]
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Title: $GW$ study of pressure-induced topological insulator transition in group IV-telluridesComments: 8 pages, 4 figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Strongly Correlated Electrons (cond-mat.str-el)
We calculate the electronic structure of the narrow gap semiconductors PbTe, SnTe and GeTe in the cubic phase using density functional theory (DFT) and the $G_0W_0$ method. Within DFT, we show that the band ordering obtained with a conventional semilocal exchange-correlation approximation is correct for SnTe and GeTe but wrong for PbTe. The correct band ordering at the high-symmetry point L is recovered adding $G_0W_0$ quasiparticle corrections. However, one-shot $G_0W_0$ produces artifacts in the band structure due to the wrong orbital character of the DFT single-particle states at the band edges close to L. We show that in order to correct these artifacts it is enough to consider the off-diagonal elements of the $G_0W_0$ self-energy corresponding to these states. We also investigate the pressure dependence of the band gap for these materials and the possibility of a transition from a trivial to a non-trivial topology of the band structure. For PbTe, we predict the band crossover and topological transition to occur at around 4.8 GPa. For GeTe, we estimate the topological transition to occur at 1.9 GPa in the constrained cubic phase, a pressure lower than the one of the structural phase transition from rombohedral to cubic. SnTe is a crystalline topological insulator at ambient pressure, and the transition into a trivial topology would take place under a volume expansion of approximately $10\%$.
Thu, 19 Mar 2020
- arXiv:2003.07857 [pdf, other]
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Title: Dynamical spin excitations of topological Haldane gapped phase in the $S=1$ Heisenberg antiferromagnetic chain with single-ion anisotropyComments: 7 pages, 8 figuresSubjects: Strongly Correlated Electrons (cond-mat.str-el); Superconductivity (cond-mat.supr-con)
We study the dynamical spin excitations of the one-dimensional $S=1$ Heisenberg antiferromagnetic chain with single-ion anisotropy by using quantum Monte Carlo simulations and stochastic analytic continuation of imaginary-time correlation function. Using the transverse dynamic spin structure factor, we observe the quantum phase transition with a critical point between the topological Haldane gapped phase and the trivial phase. At the quantum critical point, we find a broad continuum characterized by the Tomonaga-Luttinger liquid similar to a $S=1/2$ Heisenberg antiferromagnetic chain. We further identify that the elementary excitations are fractionalized spinons.
- arXiv:2003.07864 [pdf, other]
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Title: Exotic photonic molecules via Lennard-Jones-like potentialsAuthors: Przemyslaw Bienias, Michael J. Gullans, Marcin Kalinowski, Alexander N. Craddock, Dalia P. Ornelas-Huerta, Steven L. Rolston, J.V. Porto, Alexey V. GorshkovSubjects: Quantum Gases (cond-mat.quant-gas); Optics (physics.optics); Quantum Physics (quant-ph)
Ultracold systems offer an unprecedented level of control of interactions between atoms. An important challenge is to achieve a similar level of control of the interactions between photons. Towards this goal, we propose a realization of a novel Lennard-Jones-like potential between photons coupled to the Rydberg states via electromagnetically induced transparency (EIT). This potential is achieved by tuning Rydberg states to a F{\"o}rster resonance with other Rydberg states. We consider few-body problems in 1D and 2D geometries and show the existence of self-bound clusters ("molecules") of photons. We demonstrate that for a few-body problem, the multi-body interactions have a significant impact on the geometry of the molecular ground state. This leads to phenomena without counterparts in conventional systems: For example, three photons in 2D preferentially arrange themselves in a line-configuration rather than in an equilateral-triangle configuration. Our result opens a new avenue for studies of many-body phenomena with strongly interacting photons.
- arXiv:2003.07870 [pdf, other]
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Title: Time-reversal odd transport in bilayer graphene: Hall conductivity and Hall viscosityAuthors: Wei-Han HsiaoComments: 8 pages, 3 figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Strongly Correlated Electrons (cond-mat.str-el); High Energy Physics - Theory (hep-th)
We compute the time-reversal odd effective action for the low-energy model of bilayer graphene in the presence of out-of-plane magnetic field. A generating functional for the effective action that captures the electromagnetic response to all orders in momentum and frequency is presented and evaluated to the third order in space-time gradient $\mathcal O(\partial^3)$. In addition, we calculate the Hall viscosity and derive an explicit relationship with the $q^2$ coefficient of the Hall conductivity. It is reminiscent of the Hoyos-Son relation in the Galilean invariant systems, which can be recovered in the limit of large filling factor $N$ .
- arXiv:2003.07872 [pdf, ps, other]
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Title: Structure, magnetic and dielectric properties in nano-crystalline Yb$_2$CoMnO$_6$Comments: 11 pages, 15 figuresSubjects: Strongly Correlated Electrons (cond-mat.str-el)
Structural, magnetic and dielectric properties have been studied for Yb$_2$CoMnO$_6$. Nano-crystalline sample of Yb$_2$CoMnO$_6$ synthesized by sol-gel method and structural analysis shows that the sample crystallizes in monoclinic crystal structure with \textit{P2$_1$/n} phase group. To understand the charge state of Co, Mn and Yb we have performed the XPS study. Magnetic study shows that the sample undergoes a paramagnetic to ferromagnetic phase transition around $T_c$ $\sim$56 K and an additional magnetic ordering at a lower temperature around 14 K due to ordering of Yb$^{3+}$ magnetic ions. Temperature dependent Raman study reveals that spin-phonon interaction is present in this material. Further, we have studied the dielectric properties of this material. We observed that the material shows a relaxation behavior that obeys the thermally activated relaxation mechanism. Impedance spectroscopy reveals that the material shows non-Debye's behavior. AC conductivity study is performed to understand the conduction mechanics which involve the quantum mechanical tunneling phenomenon.
- arXiv:2003.07873 [pdf, other]
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Title: On the low-energy description for tunnel-coupled one-dimensional Bose gasesComments: 27 pages, 12 figuresSubjects: Quantum Gases (cond-mat.quant-gas); Quantum Physics (quant-ph)
We consider a model of two tunnel-coupled one-dimensional Bose gases with hard-wall boundary conditions. Bosonizing the model and retaining only the most relevant interactions leads to a decoupled theory consisting of a quantum sine-Gordon model and a free boson, describing respectively the antisymmetric and symmetric combinations of the phase fields. We go beyond this description by retaining the perturbation with the next smallest scaling dimension. This perturbation carries conformal spin and couples the two sectors. We carry out a detailed investigation of the effects of this coupling on the non-equilibrium dynamics of the model. We focus in particular on the role played by spatial inhomogeneities in the initial state in a quantum quench setup.
- arXiv:2003.07874 [pdf, other]
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Title: Signatures of topology in quantum quench dynamics and their interrelationComments: Updated versionSubjects: Quantum Physics (quant-ph); Quantum Gases (cond-mat.quant-gas)
Motivated by recent experimental progress in the study of quantum systems far from equilibrium, we investigate the relation between several dynamical signatures of topology in the coherent time-evolution after a quantum quench. Specifically, we study the conditions for the appearance of entanglement spectrum crossings, dynamical quantum phase transitions, and dynamical Chern numbers. For non-interacting models, we show that in general there is no direct relation between these three quantities. Instead, we relate the presence of level crossings in the entanglement spectrum to localized boundary modes that may not be of topological origin in the conventional sense. Finally, we investigate how interactions influence the presence of entanglement spectrum crossings and dynamical quantum phase transitions, by means of time-dependent density matrix renormalization group simulations.
- arXiv:2003.07875 [pdf, ps, other]
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Title: Statistics of work performed by optical tweezers with general time-variation of their stiffnessComments: 21 pages, 4 figuresSubjects: Statistical Mechanics (cond-mat.stat-mech)
We derive an exact expression for the probability density of work done on a particle that diffuses in a parabolic potential with a stiffness varying by an arbitrary piecewise constant protocol. Based on this result, the work distribution for time-continuous protocols of the stiffness can be determined up to any degree of accuracy. This is achieved by replacing the continuous driving by a piecewise constant one with a number $n$ of positive or negative steps of increasing or decreasing stiffness. With increasing $n$, the work distributions for the piecewise protocols approach that for the continuous protocol. The moment generating function of the work is given by the inverse square root of a polynomial of degree $n$, whose coefficients are efficiently calculated from a recurrence relation. The roots of the polynomials are real and positive (negative) steps of the protocol are associated with negative (positive) roots. Using these properties the inverse Laplace transform of the moment generating function is carried out explicitly. Fluctuation theorems are used to derive further properties of the polynomials and their roots.
- arXiv:2003.07881 [pdf, other]
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Title: One-dimensional moire charge density wave in the hidden order state of URu2Si2 induced by fractureAuthors: Edwin Herrera, Victor Barrena, Isabel Guillamon, Jose Augusto Galvis, William J. Herrera, Jose Castilla, Dai Aoki, Jacques Flouquet, Hermann SuderowSubjects: Strongly Correlated Electrons (cond-mat.str-el); Materials Science (cond-mat.mtrl-sci)
Moir\'e patterns can lead to fundamentally new electronic behavior when formed between two atomic lattices slightly shifted with respect to each other. A solid is however not just characterized by the atomic lattice, but also by charge or magnetic excitations that do not need to be commensurate to the lattice. This raises the question if one can obtain a moir\'e by combining periodic electronic modulations and the atomic lattice. Here we report on the discovery of a one-dimensional charge density wave (1D-CDW) which is a moir\'e pattern between the atomic lattice and a hot spot for electronic scattering in the bandstructure of the hidden order (HO) state of URu$_2$Si$_2$. The moir\'e is produced by fracturing the crystal at low temperatures. Our results suggest that charge interactions are among the most relevant features competing with HO in URu$_2$Si$_2$.
- arXiv:2003.07895 [pdf, other]
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Title: Renormalization and conformal invariance of non-local quantum electrodynamicsComments: 39 pages, 1 figureSubjects: High Energy Physics - Theory (hep-th); Strongly Correlated Electrons (cond-mat.str-el)
We study renormalization group flow in a non-local version of quantum electrodynamics (QED). We determine the regime in which the theory flows to a local theory in the infrared and study a possible UV completion of four-dimensional QED. In addition, we find that there exist non-local conformal theories with a one-dimensional conformal manifold and non-local deformations of QED in three dimensions that are exactly marginal. Along the way we develop methods for coupling non-local derivatives to external sources and discuss unitarity and conformal vs. scale invariance of these theories.
- arXiv:2003.07912 [pdf, other]
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Title: Predicting the ultimate outcome of the COVID-19 outbreak in ItalyAuthors: Gabor VattayComments: 2 pagesSubjects: Populations and Evolution (q-bio.PE); Physics and Society (physics.soc-ph)
During the COVID-19 outbreak, it is essential to monitor the effectiveness of measures taken by governments on the course of the epidemic. Here we show that there is already a sufficient amount of data collected in Italy to predict the outcome of the process. We show that using the proper metric, the data from Hubei Province and Italy has striking similarity, which enables us to calculate the expected number of confirmed cases and the number of deaths by the end of the process. Our predictions will improve as new data points are generated day by day, which can help to make further public decisions. The method is based on the data analysis of logistic growth equations describing the process on the macroscopic level. At the time of writing of the first version, the number of fatalities in Italy was expected to be 6000, and the predicted end of the crisis was April 15, 2020. In this new version, we discuss what changed in the two weeks which passed since then. The trend changed drastically on March 17, 2020, when the Italian health system reached its capacity limit. Without this limit, probably 3500 more people would have died. Instead, due to the limitations, 17.000 people are expected to die now, which is a five-fold increase. The predicted end of the crisis now shifted to May 8, 2020.
- arXiv:2003.07919 [pdf, other]
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Title: Diffusion in a biased washboard potential revisitedJournal-ref: Phys. Rev. E 101, 032123 (2020)Subjects: Statistical Mechanics (cond-mat.stat-mech); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Soft Condensed Matter (cond-mat.soft)
The celebrated Sutherland-Einstein relation for systems at thermal equilibrium states that spread of trajectories of Brownian particles is an increasing function of temperature. Here, we scrutinize diffusion of underdamped Brownian motion in a biased periodic potential and analyse regimes in which a diffusion coefficient decreases with increasing temperature within finite temperature window. Comprehensive numerical simulations of the corresponding Langevin equation performed with unprecedented resolution allow us to construct phase diagram for the occurrence of the non-monotonic temperature dependence of the diffusion coefficient. We discuss the relation of the latter effect with the phenomenon of giant diffusion.
- arXiv:2003.07925 [pdf]
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Title: Measurement of the heat flux normalised spin Seebeck coefficient of thin films as a function of temperatureSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Applied Physics (physics.app-ph)
The spin Seebeck effect (SSE) has generated interest in the thermoelectric and magnetic communities for potential high efficiency energy harvesting applications, and spintronic communities as a source of pure spin current. To understand the underlying mechanisms requires characterisation of potential materials across a range of temperatures, however, for thin films the default measurement of an applied temperature gradient (across the sample) has been shown to be compromised by the presence of thermal resistances. Here, we demonstrate a method to perform low temperature SSE measurements where instead of monitoring the temperature gradient, the heat flux passing through the sample is measured using two calibrated heat flux sensors. This has the advantage of measuring the heat loss through the sample as well as providing a reliable method to normalise the SSE response of thin film samples. We demonstrate this method with an $\text{SiO}_{2}/\text{Fe}_{3}O_{4}/\text{Pt}$ sample, where a semiconducting-insulating transition occurs at the Verwey transition, $T_{\text{V}}$, of $\text{Fe}_{3}\text{O}_{4}$ and quantify the thermomagnetic response above and below $T_{\text{V}}$.
- arXiv:2003.07927 [pdf]
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Title: Amplified Spontaneous Emission and Random Lasing in MAPbBr$_3$ Halide Perovskite Single CrystalsAuthors: A. O. Murzin (1), B. V. Stroganov (1), C. Günnemann (2), S. B. Hammouda (2), A. V. Shurukhina (1), M. S. Lozhkin (1), A. V. Emeline (1), Yu. V. Kapitonov ((1) Saint Petersburg State University, Russia, (2) Leibniz Universität Hannover, Germany)Subjects: Applied Physics (physics.app-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Halide perovskites are a promising optical gain media with high tunability and simple solution synthesis. In this study, two gain regimes, namely amplified spontaneous emission and random lasing, are demonstrated in same MAPbBr$_3$ halide perovskite single crystal. For this, photoluminescence is measured at a temperature of 4 K with pulsed femtosecond pumping by UV light with a 80 MHz repetition rate. Random lasing is observed in areas of the sample where a random resonator was formed due to cracks and crystal imperfections. In more homogeneous regions of the sample, the dominant regime is amplified spontaneous emission. These two regimes are reliably distinguished by the line width, the mode structure, the growth of the intensity after the threshold, and the degree of polarization of the radiation. The spectral localization of the stimulated emission well below the bound exciton resonance raises a question concerning the origin of the emission in halide perovskite lasers.
- arXiv:2003.07938 [pdf]
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Title: Magnetic Properties and Electronic Structure of Magnetic Topological Insulator MnBi$_2$Se$_4$Authors: Tiancong Zhu, Alexander J. Bishop, Tong Zhou, Menglin Zhu, Dante J. O'Hara, Alexander A. Baker, Shuyu Cheng, Robert C. Walko, Jacob J. Repicky, Jay A. Gupta, Chris M. Jozwiak, Eli Rotenberg, Jinwoo Hwang, Igor Žutić, Roland K. KawakamiComments: 20 pages, 9 figuresSubjects: Materials Science (cond-mat.mtrl-sci)
The intrinsic magnetic topological insulators MnBi$_2$X$_4$ (X = Se, Te) are promising candidates in realizing various novel topological states related to symmetry breaking by magnetic order. Although much progress had been made in MnBi$_2$Te$_4$, the study of MnBi$_2$Se$_4$ has been lacking due to the difficulty of material synthesis of the desired trigonal phase. Here, we report the synthesis of multilayer trigonal MnBi$_2$Se$_4$ with alternating-layer molecular beam epitaxy. Atomic-resolution scanning transmission electron microscopy (STEM) and scanning tunneling microscopy (STM) identify a well-ordered multilayer van der Waals (vdW) crystal with septuple-layer base units in agreement with the trigonal structure. Systematic thickness-dependent magnetometry studies illustrate the layered antiferromagnetic ordering as predicted by theory. Angle-resolved photoemission spectroscopy (ARPES) reveals the gapless Dirac-like surface state of MnBi$_2$Se$_4$, which demonstrates that MnBi$_2$Se$_4$ is a topological insulator above the magnetic ordering temperature. These systematic studies show that MnBi$_2$Se$_4$ is a promising candidate for exploring the rich topological phases of layered antiferromagnetic topological insulators.
- arXiv:2003.07946 [pdf, other]
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Title: AC Measurement of the Nernst effect of thin films at low temperaturesComments: 6 pages, 6 figuresSubjects: Superconductivity (cond-mat.supr-con)
We describe an alternating current method to measure the Nernst effect in superconducting thin films at low temperatures. The Nernst effect is an important tool in the understanding superconducting fluctuations and, in particular, vortex motion near critical points. However, in most materials, the Nernst signal in a typical experimental setup rarely exceeds a few $\mu$V, in some cases being as low as a few nV. DC measurements of such small signals require extensive signal processing and protection against stray pickups and offsets, limiting the sensitivity of such measurements to $>$5nV. Here we describe a method utilizing a one-heater-two-thermometer setup with the heating element and thermometers fabricated on-chip with the sample, which helped to reduce thermal load and temperature lag between the substrate and thermometer. Using AC heating power and 2$\omega$ measurement, we are able to achieve sub-nanovolt sensitivity in 20-30nm MoGe thin films on glass substrate, compared to a sensitivity of $\sim$9nV using DC techniques on the same setup.
- arXiv:2003.07973 [pdf, other]
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Title: Optimal isotropic, reusable truss lattice material with near-zero Poisson's ratioAuthors: Xueyan Chen (1,2), Johnny Moughames (2), Qingxiang Ji (1,2), Julio Andrés Iglesias Martínez (2), Huifeng Tan (1), Samia Adrar (2), Nicolas Laforge (2), Jean-Marc Cote (2), Sébastien Euphrasie (2), Gwenn Ulliac (2), Muamer Kadic (2), Vincent Laude (2) ((1) National Key Laboratory of Science and Technology on Advanced Composites in Special Environments, Harbin Institute of Technology Harbin, PR China, (2) Institut FEMTO-ST, CNRS, Université Bourgogne Franche-Comté, Besançon, France)Comments: 5 figuresSubjects: Applied Physics (physics.app-ph); Materials Science (cond-mat.mtrl-sci)
Cork is a natural amorphous material with near-zero Poisson's ratio that is ubiquitously used for sealing glass bottles. It is an anisotropic, transversally isotropic, composite that can hardly be scaled down. Here, we propose a new class of isotropic and reusable cork-like metamaterial that is designed from an hybrid truss-lattice material to show an isotropic Poisson's ratio close to zero. Optimization is conducted using a multi-objective genetic algorithm, assisted by an elliptical basis function neural network, and coupled with finite element simulations. The optimal micro-structured metamaterial, fabricated by two-photon lithography with a lattice constant of 300 \micro\meter, has an almost isotropic Poisson's ratio smaller than 0.08 in all directions. It can recover $96.6\%$ of its original shape after a compressional test exceeding $20\%$ strain.
- arXiv:2003.07986 [pdf, other]
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Title: Biexciton State Energies from Many-Body Perturbation Theory Based on Density Functional Theory SimulationSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We develop a method for computing self-energy of a biexciton state in a semiconductor nanostructure using many-body perturbation theory (MBPT) based on the density functional theory (DFT) simulation. We compute energies of low-energy biexciton states composed of singlet excitons in the chiral single-wall carbon nanotubes (SWCNT), such as (6,2), (6,5) and (10,5). In all cases we find a small decrease in the biexciton gap: -0.045 $eV$ in (6,2), which is 4.59\% of the non-interacting biexciton gap; -0.041 $eV$ in (6,5), which is 4.47\% of the non-interacting gap and -0.036 $eV$ in (10,5), which is 4.31\%.
- arXiv:2003.07994 [pdf, other]
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Title: Fermion dynamical symmetry and strongly-correlated electrons: a comprehensive model of high-temperature superconductivityComments: 62 pages, 56 figures, accepted for publication Frontiers of PhysicsJournal-ref: Frontiers of Physics 15(4), 43301 (2020)Subjects: Superconductivity (cond-mat.supr-con); Strongly Correlated Electrons (cond-mat.str-el); Nuclear Theory (nucl-th)
We review application of the SU(4) model of strongly-correlated electrons to cuprate and iron-based superconductors. A minimal self-consistent generalization of BCS theory to incorporate antiferromagnetism on an equal footing with pairing and strong Coulomb repulsion is found to account systematically for the major features of high-temperature superconductivity, with microscopic details of the parent compounds entering only parametrically. This provides a systematic procedure to separate essential from peripheral, suggesting that many features exhibited by the high-$T\tsub c$ data set are of interest in their own right but are not central to the superconducting mechanism. More generally, we propose that the surprisingly broad range of conventional and unconventional superconducting and superfluid behavior observed across many fields of physics results from the systematic appearance of similar algebraic structures for the emergent effective Hamiltonians, even though the microscopic Hamiltonians of the corresponding parent states may differ radically from each other.
- arXiv:2003.08007 [pdf, other]
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Title: Analysis of the Mobility-Limiting Mechanisms of the Two-Dimensional Hole Gas on Hydrogen-Terminated DiamondAuthors: Ricardo Peterson, Mohamadali Malakoutian, Xiaoqing Xu, Caitlin Chapin, Srabanti Chowdhury, Debbie G. SeneskyComments: 11 pages, 7 figuresSubjects: Applied Physics (physics.app-ph); Materials Science (cond-mat.mtrl-sci)
Here we present an analysis of the mobility-limiting mechanisms of a two-dimensional hole gas on hydrogen-terminated diamond surfaces. The scattering rates of surface impurities, surface roughness, non-polar optical phonons, and acoustic phonons are included. Using a Schrodinger/Poisson solver, the heavy hole, light hole, and split-off bands are treated separately. To compare the calculations with experimental data, Hall-effect structures were fabricated and measured at temperatures ranging from 25 to 700 K, with hole sheet densities ranging from 2 to 6$\times10^{12}\;\text{cm}^{-2}$ and typical mobilities measured from 60 to 100 cm$^{2}$/(V$\cdot$s) at room temperature. Existing data from literature was also used, which spans sheet densities above 1$\times10^{13}\;\text{cm}^{-2}$. Our analysis indicates that for low sheet densities, surface impurity scattering by charged acceptors and surface roughness are not sufficient to account for the low mobility. Moreover, the experimental data suggests that long-range potential fluctuations exist at the diamond surface, and are particularly enhanced at lower sheet densities. Thus, we propose a second type of surface impurity scattering which is caused by disorder related to the C-H dipoles.
- arXiv:2003.08018 [pdf, other]
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Title: Simulated coherent electron shuttling in silicon quantum dotsComments: 18 pages, 7 figures. Typos corrected and other minor changes in this version. Supplementary Material available upon requestSubjects: Quantum Physics (quant-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Shuttling of single electrons in gate-defined silicon quantum dots is numerically simulated. A minimal gate geometry without explicit tunnel barrier gates is introduced, and used to define a chain of accumulation mode quantum dots, each controlled by a single gate voltage. One-dimensional potentials are derived from a three-dimensional electrostatic model, and used to construct an effective Hamiltonian for efficient simulation. Control pulse sequences are designed by maintaining a fixed adiabaticity, so that different shuttling conditions can be systematically compared. We first use these tools to optimize the device geometry for maximum transport velocity, considering only orbital states and neglecting valley and spin degrees of freedom. Taking realistic geometrical constraints into account, charge shuttling speeds up to ~ 300 m/s preserve adiabaticity. Coherent spin transport is simulated by including spin-orbit and valley terms in an effective Hamiltonian, shuttling one member of a singlet pair and tracking the entanglement fidelity. With realistic device and material parameters, shuttle speeds in the range 10-100 m/s with high spin entanglement fidelities are obtained when the tunneling energy exceeds the Zeeman energy. High fidelity also requires the inter-dot valley phase difference to be below a threshold determined by the ratio of tunneling and Zeeman energies, so that spin-valley-orbit mixing is weak. In this regime, we find that the primary source of infidelity is a coherent spin rotation that is correctable, in principle. The results pertain to proposals for large-scale spin qubit processors in isotopically purified silicon that rely on coherent shuttling of spins to rapidly distribute quantum information between computational nodes.
- arXiv:2003.08020 [pdf, ps, other]
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Title: Superconductivity in hexagonal Nb-Mo-Ru-Rh-Pd high-entropy alloysJournal-ref: Scripta Materialia 182, 109 (2020)Subjects: Superconductivity (cond-mat.supr-con)
We report the superconducting properties of new hexagonal Nb$_{10+2x}$Mo$_{35-x}$Ru$_{35-x}$Rh$_{10}$Pd$_{10}$ high-entropy alloys (HEAs) (0 $\leq$ $x$ $\leq$ 5). With increasing $x$, the superconducting transition temperature $T_{\rm c}$ shows a maximum of 6.19 K at $x$ = 2.5, while the zero-temperature upper critical field $B_{\rm c2}$(0) increases monotonically, reaching 8.3 T at $x$ = 5. For all $x$ values, the specific heat jump deviates from the Bardeen-Cooper-Schreiffer behavior. In addition, we show that $T_{\rm c}$ of these HEAs is not determined mainly by the density of states at the Fermi level and would be enhanced by lowering the valence electron concentration.
- arXiv:2003.08025 [pdf]
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Title: Pressure-induced inverse order-disorder transition in double perovskitesAuthors: Zheng Deng, Chang-Jong Kang, Mark Croft, Wenmin Li, Xi Shen, Jianfa Zhao, Richeng Yu, Changqing Jin, Gabi Kotliar, Sizhan Liu, T. A. Tyson, Ryan Tappero, Martha GreenblattComments: 12 pages, 4 figures, 1 tableJournal-ref: Angewandte Chemie International Edition 59, 8240 (2020)Subjects: Materials Science (cond-mat.mtrl-sci); Strongly Correlated Electrons (cond-mat.str-el)
Given the consensus that pressure improves cation order in most of known materials, a discovery of pressure-induced disorder could require reconsideration of order-disorder transition in solid state physics/chemistry and geophysics. Double perovskites Y2CoIrO6 and Y2CoRuO6 synthesized at ambient pressure show B-site order, while the polymorphs synthesized at 6 and 15 GPa are partially-ordered and disordered respectively. With the decrease of ordering degrees, the lattices are shrunken and the crystal structures alter from monoclinic to orthorhombic symmetry. Correspondingly, long-range ferrimagnetic order in the B-site ordered phases are gradually overwhelmed by B-site disorder. Theoretical calculations suggest that unusual unit cell compressions under external pressures unexpectedly stabilize the disordered phases of Y2CoIrO6 and Y2CoRuO6.
- arXiv:2003.08029 [pdf, ps, other]
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Title: Topological degeneracy in Ising chain induced by dissipationComments: 7 pages, 2 figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Strongly Correlated Electrons (cond-mat.str-el); Quantum Physics (quant-ph)
The groundstate degeneracy of quantum spin system is a characteristic of non-trivial topology, when it is gapped and robust against disordered perturbation. The corresponding quantum phase transition (QPT) is usually driven by a real parameter. We study a non-Hermitian Ising chain with two transverse fields, one real another imaginary, based on the exact solution and numerical simulation. We show that topological degeneracy still exists, and can be obtained by an imaginary transverse field from a topologically trivial phase of a Hermitian system. The topological degeneracy is robust against random imaginary field, and therefore expected to be immune to disordered dissipation from the spontaneous decay in experiment. The underlying mechanism is the nonlocal symmetry, which emerges only in thermodynamic limit and unifies two categories of QPTs in quantum spin system, rooted from topological order and symmetry breaking, respectively.
- arXiv:2003.08035 [pdf]
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Title: Thermally induced generation and annihilation of magnetic chiral skyrmion bubbles and achiral bubbles in Mn-Ni-Ga MagnetsAuthors: Bei Ding, Junwei Zhang, Hang Li, Senfu Zhang, Enke Liu, Guangheng Wu, Xixiang Zhang, Wenhong WangComments: 15 pages,4 figuresJournal-ref: Appl. Phys. Lett, 116, 132402 (2020)Subjects: Materials Science (cond-mat.mtrl-sci)
Magnetic chiral skyrmion bubbles and achiral bubbles are two independent magnetic domain structures, in which the former with equivalent winding number to skyrmions offers great promise as information carriers for further spintronic devices. Here, in this work, we experimentally investigate the generation and annihilation of magnetic chiral skyrmion bubbles and achiral bubbles in the Mn-Ni-Ga thin plate by using the Lorentz transmission electron microscopy (L-TEM). The two independent magnetic domain structures can be directly controlled after the field cooling manipulation by varying the titled angles of external magnetic fields. By imaging the magnetization reversal with increasing temperature, we found an extraordinary annihilation mode of magnetic chiral skyrmion bubbles and a non-linear frequency for the winding number reversal. Quantitative analysis of such dynamics was performed by using L-TEM to directly determine the barrier energy for the magnetization reversal of magnetic chiral skyrmion bubbles.
- arXiv:2003.08046 [pdf, other]
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Title: Achieving 50 femtosecond resolution in MeV ultrafast electron diffraction with a double bend achromat compressorAuthors: Fengfeng Qi, Zhuoran Ma, Lingrong Zhao, Yun Cheng, Wenxiang Jiang, Chao Lu, Tao Jiang, Dong Qian, Zhe Wang, Wentao Zhang, Pengfei Zhu, Xiao Zou, Weishi Wan, Dao Xiang, Jie ZhangComments: Accepted for publication in Physical Review LetersSubjects: Accelerator Physics (physics.acc-ph); Materials Science (cond-mat.mtrl-sci); Atomic and Molecular Clusters (physics.atm-clus)
We propose and demonstrate a novel scheme to produce ultrashort and ultrastable MeV electron beam. In this scheme, the electron beam produced in a photocathode radio-frequency (rf) gun first expands under its own Coulomb force with which a positive energy chirp is imprinted in the beam longitudinal phase space. The beam is then sent through a double bend achromat with positive longitudinal dispersion where electrons at the bunch tail with lower energies follow shorter paths and thus catch up with the bunch head, leading to longitudinal bunch compression. We show that with optimized parameter sets, the whole beam path from the electron source to the compression point can be made isochronous such that the time of flight for the electron beam is immune to the fluctuations of rf amplitude. With a laser-driven THz deflector, the bunch length and arrival time jitter for a 20 fC beam after bunch compression are measured to be about 29 fs (FWHM) and 22 fs (FWHM), respectively. Such an ultrashort and ultrastable electron beam allows us to achieve 50 femtosecond (FWHM) resolution in MeV ultrafast electron diffraction where lattice oscillation at 2.6 THz corresponding to Bismuth A1g mode is clearly observed without correcting both the short-term timing jitter and long-term timing drift. Furthermore, oscillating weak diffuse scattering signal related to phonon coupling and decay is also clearly resolved thanks to the improved temporal resolution and increased electron flux. We expect that this technique will have a strong impact in emerging ultrashort electron beam based facilities and applications.
- arXiv:2003.08055 [pdf, other]
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Title: Floquet Topological Phases of Non-Hermitian Disordered SystemsComments: 7 pages, 4 figuresSubjects: Disordered Systems and Neural Networks (cond-mat.dis-nn); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Quantum Physics (quant-ph)
The non-Hermiticity caused breakdown of bulk-boundary correspondence in topological phase transition was curled by considering the skin effect for the chirally symmetric systems. However, as a powerful tool in engineering exotic topological phases, periodic driving cannot preserve the chiral symmetry of the systems. Here, we investigate the topological phases of periodically driven one-dimensional non-Hermitian disordered system. Using Floquet theorem, we propose a scheme to retrieve the bulk-boundary correspondence and establish a general description to the topological phase transition for such nonequilibrium system. The exemplification of our method in the non-Hermitian Su-Schrieffer-Heeger model shows that diverse exotic topological phases absent in the static case are induced by the periodic driving. Further study reveals that the extra non-Hermitian Floquet topological Anderson insulator phases are induced by the disorder. Our result supplies a useful way to artificially synthesize exotic phases by periodic driving in the non-Hermitian system.
- arXiv:2003.08057 [pdf, ps, other]
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Title: Anomalous thermodynamics of lattice Bose gases in optical cavitiesComments: 5+1 pages, 3 figuresSubjects: Quantum Gases (cond-mat.quant-gas)
We investigate thermodynamic properties of lattice Bose gases in optical cavities in the Mott-insulator limit. We find the system assumes anomalous thermodynamic behavior that can be traced back to the breaking of fundamental additivity by its infinite-long range interaction. Specifically, the system shows striking ensemble inequivalence between the canonical ensemble and the grand canonical one, sharply manifesting in the distinct anomalous structure of the thermodynamic phase diagram in the canonical ensemble. In particular, in the temperature regime around half of the on-site energy, the system manifests negative compressibility and anomalous reentrant phase transitions where the ordered charge density wave phase revives from the disordered homogenous phase upon increasing the temperature. Direct experimental observation of the anomalous behavior can be realized in the current experiments with well-controlled total particle number fluctuations.
- arXiv:2003.08084 [pdf, other]
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Title: Interplay between collective modes in hybrid electron gas-superconductor structuresJournal-ref: Phys. Rev. B 101, 165430 (2020)Subjects: Superconductivity (cond-mat.supr-con)
We study hybridization of collective plasmon and Carlson-Goldman-Artemenko-Volkov modes in a hybrid system, consisting of a two-dimensional layers of electron gas in the normal state and superconductor, coupled by long-range Coulomb forces. The interaction between these collective modes is not possible in a regular single-layer two-dimensional system since they exist in non-overlapping domains of dimensionless parameter $\omega\tau$, where $\omega$ is the external electromagnetic field frequency and $\tau$ is electron scattering time. Thus, in a single-layer structure, these modes are mutually exclusive. However, the coupling may become possible in a hybrid system consisting of two separated in space materials with different properties, in particular, the electron scattering time. We investigate the electromagnetic power absorption by the hybrid system and reveal the conditions necessary for the hybridization of collective modes.
- arXiv:2003.08100 [pdf, ps, other]
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Title: Exponential volume-dependence of entropy current fluctuations at first-order phase transitionsComments: 9 pages, 2 figuresSubjects: Statistical Mechanics (cond-mat.stat-mech)
In chemical reaction networks, bistability can only occur far from equilibrium. It is associated with a first-order phase transition where the control parameter is the thermodynamic force. At the bistable point, the entropy production is known to be discontinuous. We show that the fluctuations of the entropy production have an exponential volume-dependence when the system is bistable. At the phase transition, the exponential prefactor is the height of the effective potential barrier between the two fixed-points. Our results obtained for Schl\"ogl's model can be extended to any chemical network.
- arXiv:2003.08101 [pdf, other]
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Title: Direct control of high magnetic fields for cold atom experiments based on NV centersAuthors: Alexander Hesse, Kerim Köster, Jakob Steiner, Julia Michl, Vadim Vorobyov, Durga Dasari, Jörg Wrachtrup, Fred JendrzejewskiSubjects: Applied Physics (physics.app-ph); Quantum Gases (cond-mat.quant-gas); Atomic Physics (physics.atom-ph); Quantum Physics (quant-ph)
In atomic physics experiments, magnetic fields allow to control the interactions between atoms, eg. near Feshbach resonances, or by employing spin changing collisions. The magnetic field control is typically performed indirectly, by stabilizing the current of Helmholtz coils producing the large bias field. Here, we overcome the limitations of such an indirect control through a direct feedback scheme, which is based on nitrogen-vacancy centers acting as a sensor. This allows us to measure and stabilize magnetic fields of 46.6 G down to 1.2 mG RMS noise, with the potential of reaching much higher field strengths. Because the magnetic field is measured directly, we reach minimum shot-to-shot fluctuations of 0.32(4) ppm on a 22 minute time interval, ensuring high reproducibility of experiments. This approach extends the direct magnetic field control to high magnetic fields, which could enable new precise quantum simulations in this regime.
- arXiv:2003.08115 [pdf, other]
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Title: Interaction of charged impurities and Rydberg excitons in cuprous oxideComments: 6 pages, 4 figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We investigate the influence of a static, uncorrelated distribution of charged impurities on the spectrum of bound excitons in the copper oxide Cu$_{\text{2}}$O. We show that the statistical distribution of Stark shifts and ionisation rates leads to the vanishing of Rydberg resonances into an apparent continuum. The appearance of additional absorption lines due to the broken rotational symmetry, together with spatially inhomogeneous Stark shifts, leads to a modification of the observed line shapes that agree qualitatively with the changes observed in the experiment.
- arXiv:2003.08120 [pdf, other]
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Title: Time's Arrow and the Fragility of Topological PhasesComments: 3 + 4 Pages, 1 FigureSubjects: Strongly Correlated Electrons (cond-mat.str-el); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Statistical Mechanics (cond-mat.stat-mech); Quantum Physics (quant-ph)
The second law of thermodynamics points to the existence of an `arrow of time', along which entropy only increases. This arises despite the time-reversal symmetry (TRS) of the microscopic laws of nature. Within quantum theory, TRS underpins many interesting phenomena, most notably topological insulators and the Haldane phase of quantum magnets. Here, we demonstrate that such TRS-protected effects are fundamentally unstable against coupling to an environment. In analogy to the appearance of time's arrow, this is not because of microscopic symmetry breaking, but due to an emergent effect. Just as irreversible entanglement entropy production is facilitated by coupling a quantum system to its surroundings, TRS-protected phenomena are spoiled if the system forms part of some larger `universe'. Our results highlight the enigmatic nature of TRS in quantum mechanics, and elucidate potential challenges in utilising topological systems for quantum technologies.
- arXiv:2003.08127 [pdf]
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Title: Electronic transport and magnetism in the alternating stack of metallic and highly frustrated magnetic layers in Co$_{1/3}$NbS$_2$Authors: Petar Popčević, Ivo Batistić, Ana Smontara, Kristijan Velebit, Jaćim Jaćimović, Edoardo Martino, Ivica Živković, Nikolay Tsyrulin, Julian Piatek, Helmuth Berger, Andrey A. Sidorenko, Henrik M. Rønnow, Neven Barišić, László Forró, Eduard TutišComments: 34 pages, 17 figuresSubjects: Strongly Correlated Electrons (cond-mat.str-el)
Co$_{1/3}$NbS$_2$ is the only magnetically intercalated layered transition metal dichalcogenide (TMD) suggested to experience the complete suppression of magnetic order under pressure. From elastic neutron scattering we report the direct evidence for the reduction of the antiferromagnetic ordering temperature under pressure, up to complete suppression of magnetic order around 1.7 GPa. The static and ac magnetic susceptibility measurements reveal strong frustration in the magnetic subsystem, and spin canting responsible for the appearance of ferromagnetic (FM) component in dominantly antiferromagnetic (AF) ordered state. The electric transport in directions perpendicular and parallel to layers is explored for the first time in magnetically intercalated TMDs, in the wide temperature and pressure ranges. We show that electric transport reacts differently to magnetic ordering in directions along and perpendicular to layers, with the in-plane conductivity increasing, and the out-of-plane conductivity decreasing in the ordered state. At pressures above 3 GPa, we identify the appearance of the Kondo scattering regime. We use ab-initio calculations to explore the electronic structure in magnetically ordered state, the nature of magnetic interactions, and the mechanism responsible for the changes observed under pressure. The mechanisms of suppression of magnetic order under pressure are scrutinized in the light of these experimental and theoretical findings. We conclude that magnetic couplings beyond nearest-neighbors determine the nature of magnetic ordering. The suppression of ordering under pressure is ascribed to the pressure-induced shift in balance between super-exchange and Ruderman-Kittel-Kasuya-Yosida (RKKY) magnetic couplings, leading to amplified magnetic frustration.
- arXiv:2003.08140 [pdf]
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Title: Experimental discovery of bulk-disclination correspondenceSubjects: Materials Science (cond-mat.mtrl-sci); Optics (physics.optics)
The past decade has witnessed the emergence of abundant topological phases protected by crystalline symmetries, such as topological crystalline insulators (TCIs) [1-3]. Recent discoveries of higher-order [4-7] and fragile [8-11] TCIs illustrate that gapless edge states may not be a universal feature of TCIs, and thus request alternative experimental signatures. Here, we demonstrate that disclinations, i.e., rotational topological defects in crystals, can serve as a novel probe of TCIs without invoking edge boundaries. Using photonic crystals, i.e., artificial periodic structures giving access to versatile manipulations of light [12], we observe topologically-protected photonic modes localized at disclinations in photonic TCIs. We create physical realizations of photonic TCIs and disclinations using macroscopic dielectric structures based on hexagonal lattices. By driving the photonic system across a topological transition through tuning the unit-cell geometry, we find that the topological disclination modes disappear in the trivial phase. The experimental discovery of the bulk-disclination correspondence unveils a new horizon in topological physics, while its photonic realization provides a pathway toward topological photonics [13-23] beyond the bulk-edge correspondence.
- arXiv:2003.08143 [pdf, other]
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Title: Exciton energy oscillations induced by quantum beatsAuthors: A. V. Trifonov, A. S. Kurdyubov, I. Ya. Gerlovin, D. S. Smirnov, K. V. Kavokin, I. A. Yugova, M. Aßmann, A. V. KavokinComments: 6 pages, 4 figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
In this paper, we experimentally demonstrate an oscillating energy shift of quantum-confined exciton levels in a semiconductor quantum well after excitation into a superposition of two quantum confined exciton states of different parity. Oscillations are observed at frequencies corresponding to the quantum beats between these states. We show that the observed effect is a manifestation of the exciton density oscillations in the real space similar to the dynamics of a Hertzian dipole. The effect is caused by the exciton-exciton exchange interaction and appears only if the excitons are in a superposition quantum state. Thus, we have found clear evidence for the incoherent exchange interaction in the coherent process of quantum beats. This effect may be harnessed for quantum technologies requiring the quantum coherence of states.
- arXiv:2003.08147 [pdf]
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Title: The performance limits of epigraphene Hall sensorsAuthors: Hans He, Naveen Shetty, Thilo Bauch, Sergey Kubatkin, Timo Kaufmann, Martin Cornills, Rositsa Yakimova, Samuel Lara-AvilaSubjects: Materials Science (cond-mat.mtrl-sci); Applied Physics (physics.app-ph); Instrumentation and Detectors (physics.ins-det)
Epitaxial graphene on silicon carbide, or epigraphene, provides an excellent platform for Hall sensing devices in terms of both high electrical quality and scalability. However, the challenge in controlling its carrier density has thus far prevented systematic studies of epigraphene Hall sensor performance. In this work we investigate epigraphene Hall sensors where epigraphene is doped across the Dirac point using molecular doping. Depending on the carrier density, molecular-doped epigraphene Hall sensors reach room temperature sensitivities $S_V=0.23 V/VT$,$S_I=1440 V/AT$ and magnetic field detection limits down to $B_{MIN}=27$ $nT/\sqrt{Hz}$ at 20 kHz. Thermally stabilized devices demonstrate operation up to $T=150$ $^oC$ with $S_V=0.12 V/VT$, $S_I=300 V/AT$ and $B_{MIN}\approx 100$ $nT/\sqrt{Hz}$ at 20 kHz.
- arXiv:2003.08148 [pdf, ps, other]
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Title: Linear mapping between magnetic susceptibility and entanglement in conventional and exotic one-dimensional superfluidsSubjects: Quantum Gases (cond-mat.quant-gas); Strongly Correlated Electrons (cond-mat.str-el); Superconductivity (cond-mat.supr-con); Quantum Physics (quant-ph)
We investigate the mapping between magnetic susceptibility and entanglement in the metallic, insulating, conventional and exotic polarized superfluid phases of one-dimensional fermionic lattice systems as described by the Hubbard model. Motivated by recent proposals for determining and quantifying entanglement via magnetic susceptibility measurements, we numerically study the intrinsic relationship between the two quantities at zero temperature. We find signatures of the metal-insulator transition and of the BCS-BEC crossover, but the most relevant result is that for conventional and exotic superfluids the mapping between magnetic susceptibility and entanglement is surprisingly simple: inversely proportional. This linear behavior could be exploited to quantify entanglement in current cold-atoms and condensed-matter experiments.
- arXiv:2003.08153 [pdf, other]
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Title: Refined diamond norm bounds on the emergence of objectivity of observablesComments: 22 pages, 2 figuresSubjects: Quantum Physics (quant-ph); Statistical Mechanics (cond-mat.stat-mech); High Energy Physics - Theory (hep-th); Mathematical Physics (math-ph)
The theory of Quantum Darwinism aims to explain how our objective classical reality arises from the quantum world, by analysing the distribution of information about a quantum system that is accessible to multiple observers, who probe the system by intercepting fragments of its environment. Previous work showed that, when the number of environmental fragments grows, the quantum channels modelling the information flow from system to observers become arbitrarily close - in terms of diamond norm distance - to "measure-and-prepare" channels, ensuring objectivity of observables; the convergence is formalised by an upper bound on the diamond norm distance, which decreases with increasing number of fragments. Here, we derive tighter diamond norm bounds on the emergence of objectivity of observables for quantum systems of arbitrary (finite or infinite) dimension. Furthermore, we probe the tightness of our bounds by considering a specific model of a system-environment dynamics given by a pure loss channel. Finally, we generalise to infinite dimensions a result obtained by Brand\~{a}o et al. [Nat. Commun. 6, 7908 (2015)], which provides an operational characterisation of quantum discord in terms of one-sided redistribution of correlations to many parties. Our results provide an improved and unified framework to benchmark quantitatively the rise of objectivity in the quantum-to-classical transition.
- arXiv:2003.08155 [pdf, other]
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Title: Velocity and diffusion constant of an active particle in a one dimensional force fieldComments: 7 + 15 pages, 8 figuresSubjects: Statistical Mechanics (cond-mat.stat-mech); Disordered Systems and Neural Networks (cond-mat.dis-nn); Soft Condensed Matter (cond-mat.soft)
We consider a run an tumble particle with two velocity states $\pm v_0$, in an inhomogeneous force field $f(x)$ in one dimension. We obtain exact formulae for its velocity $V_L$ and diffusion constant $D_L$ for arbitrary periodic $f(x)$ of period $L$. They involve the "active potential" which allows to define a global bias. Upon varying parameters, such as an external force $F$, the dynamics undergoes transitions from non-ergodic trapped states, to various moving states, some with non analyticities in the $V_L$ versus $F$ curve. A random landscape in the presence of a bias leads, for large $L$, to anomalous diffusion $x \sim t^\mu$, $\mu<1$, or to a phase with a finite velocity that we calculate.
- arXiv:2003.08156 [pdf, other]
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Title: A stochastic thermopotentiostat for molecular dynamicsSubjects: Materials Science (cond-mat.mtrl-sci); Chemical Physics (physics.chem-ph); Computational Physics (physics.comp-ph)
We derive a stochastic approach to sample the canonical ensemble at constant temperature and applied electric potential. Our proposed thermopotentiostat is the electrical analog to the Langevin thermostat. It is free of simulation artefacts, avoiding any spurious energy transfer between kinetic and electric degrees of freedom. Our approach can be straightforwardly applied in the context of \emph{ab initio} molecular dynamics calculations. Using thermopotentiostat molecular dynamics simulations, we explore the interfacial dielectric properties of nano-confined water.
- arXiv:2003.08160 [pdf, ps, other]
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Title: Three-dimensional phase transitions in multiflavor lattice scalar SO(Nc) gauge theoriesComments: 9 pagesSubjects: Statistical Mechanics (cond-mat.stat-mech); High Energy Physics - Lattice (hep-lat)
We investigate the phase diagram and finite-temperature transitions of three-dimensional scalar SO(Nc) gauge theories with Nf scalar flavors. These models are constructed starting from a maximally O(N)-symmetric multicomponent scalar model (N = Nc Nf), whose symmetry is partially gauged to obtain an SO(Nc) gauge theory, with O(Nf) or U(Nf) global symmetry for Nc > 2 or Nc = 2, respectively. These systems undergo finite-temperature transitions, where the global symmetry is broken. Their nature is discussed using the Landau-Ginzburg-Wilson (LGW) approach, based on a gauge-invariant order parameter, and the continuum scalar SO(Nc) gauge theory. The LGW approach predicts that the transition is of first order for Nf > 2. For Nf = 2 the transition is predicted to be continuous: it belongs to the O(3) vector universality class for Nc=2 and to the XY universality class for any Nc > 2. We perform numerical simulations for Nc = 3 and Nf = 2,3. The numerical results are in agreement with the LGW predictions.
- arXiv:2003.08167 [pdf, other]
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Title: Critical behavior at the integer quantum Hall transition in a network model on the Kagome latticeComments: 9 pages, 5 figuresSubjects: Disordered Systems and Neural Networks (cond-mat.dis-nn)
We study a network model on the Kagome lattice (NMKL). This model generalizes the Chalker-Coddington (CC) network model for the integer quantum Hall transition. Unlike random network models we studied earlier, the geometry of the Kagome lattice is regular. Therefore, we expect that the critical behavior of the NMKL should be the same as that of the CC model. We numerically compute the localization length index $\nu$ in the NKML. Our result $\nu= 2.658 \pm 0.046$ is close to CC model values obtained in a number of recent papers. We also map the NMKL to the Dirac fermions in random potentials and in a fixed periodic curvature background. The background turns out irrelevant at long scales. Our numerical and analytical results confirm our expectation of the universality of critical behavior on regular network models.
- arXiv:2003.08174 [pdf]
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Title: Pickling Behaviour of 2205 Duplex Stainless Steel Hot-rolled Strips in Sulfuric Acid ElectrolytesComments: 12 pages, 14 figures,3 tablesSubjects: Applied Physics (physics.app-ph)
Pickling behaviour of the oxide layer on hot-rolled 2205 duplex stainless steel (DSS) was studied in H2SO4 solutions with electrolytic workstation.
- arXiv:2003.08176 [pdf, other]
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Title: A computational study of viscoelastic blood flow in an arteriovenous fistulaSubjects: Medical Physics (physics.med-ph); Soft Condensed Matter (cond-mat.soft); Computational Physics (physics.comp-ph)
A finite element analysis of flows of an Oldroyd-B fluid is developed, to simulate blood flow in an arteriovenous fistula. The model uses a combination of a standard conforming finite element approximation for the momentum equation, and the discontinuous Galerkin method, with upwinding, for the equation governing the evolution of the extra stress. The model is verified for a range of values of Weissenberg number We by applying it to the benchmark problem of flow past a cylinder in a channel. The main application is to flow in an arteriovenous fistula, the geometry of which is based on patient-specific data. Results for Oldroyd-B fluids are compared with those for a Newtonian fluid as well as with data from patient-specific velocity MRI scans. Features such as streamlines and regions of recirculation are similar across a range of values of We and the Newtonian case. There is however a strong dependence of maximum wall shear stress on We, with values for the viscoelastic fluid in all cases being higher than that for the Newtonian case.
- arXiv:2003.08183 [pdf, ps, other]
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Title: Universal behavior in the Nernst effect of heavy fermion materialsAuthors: Yi-feng YangComments: 6 pages, 4 figuresSubjects: Strongly Correlated Electrons (cond-mat.str-el)
We report the observation of a universal scaling of the Nernst coefficient over a wide intermediate temperature range in the heavy fermion superconductors CeCu$_2$Si$_2$, CeCoIn$_5$, and Ce$_2$PdIn$_8$, the ferromagnetic Kondo lattice Ce$_3$RhSi$_3$, the nonmagnetic CeRu$_2$Si$_2$, the intermediate valent YbAl$_3$, and the hidden order compound URu$_2$Si$_2$, that cover a broad spectrum of heavy fermion materials with different crystal, valence and ground state properties. The scaling formula follows exactly the magnetic susceptibility of emergent heavy quasiparticles as predicted in the two-fluid model. We give a tentative explanation of the scaling based on the skew scattering mechanism and argue that the Nernst effect is produced by the asymmetry of the quasiparticle density of states rather than that of the scattering rate. In URu$_2$Si$_2$, the giant Nernst signal in the hidden order phase is also found to follow the predicted scaling, indicating the potential involvement of hybridization physics. Our work suggests a unified picture for the Nernst effect in heavy fermion materials and provides a promising basis for the development of a better theory in the future.
- arXiv:2003.08212 [pdf]
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Title: Effect of electric current on optical orientation of electrons in AlGaAs/GaAs heterostructureAuthors: O. S. Ken (1), E. A. Zhukov (1 and 2), I. A. Akimov (1 and 2), V. L. Korenev (1), N. E. Kopteva (2 and 3), I. V. Kalitukha (1), V. F. Sapega (1), A. D. Wieck (4), A. Ludwig (4), R. Schott (4), Yu. G. Kusrayev (1), D. R. Yakovlev (1 and 2), M. Bayer (1 and 2) ((1) Ioffe Institute, Russian Academy of Sciences, St. Petersburg, Russia, (2) Experimentelle Physik 2, Technische Universitaet Dortmund, Dortmund, Germany, (3) Spin Optics Laboratory, St. Petersburg State University, Petersburg, Russia, (4) Fakultaet fuer Physik und Astronomie, Ruhr-Universitaet Bochum, Bochum, Germany)Comments: 21 pages, 7 figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
The effect of a lateral electric current on the photoluminescence H-band of an AlGaAs/GaAs heterostructure is investigated. The photoluminescence intensity and optical orientation of electrons contributing to the H-band are studied by means of continuous wave and time-resolved photoluminescence spectroscopy and time-resolved Kerr rotation. It is shown that the H-band is due to recombination of the heavy holes localized at the heterointerface with photoexcited electrons attracted to the heterointerface from the GaAs layer. Two lines with significantly different decay times constitute the H-band: a short-lived high-energy one and a long-lived low-energy one. The high-energy line originates from recombination of electrons freely moving along the structure plane, while the low-energy one is due to recombination of donor-bound electrons near the interface. Application of the lateral electric field of ~ 100-200 V/cm results in a quenching of both lines. This quenching is due to a decrease of electron concentration near the heterointerface as a result of a photocurrent-induced heating of electrons in the GaAs layer. On the contrary, electrons near the heterointerface are effectively cooled, so the donors near the interface are not completely empty up to ~ 100 V/cm, which is in stark contrast with the case of bulk materials. The optical spin polarization of the donor-bound electrons near the heterointerface weakly depends on the electric field. Their polarization kinetics is determined by the spin dephasing in the hyperfine fields of the lattice nuclei. The long spin memory time (> 40 ns) can be associated with suppression of the Bir-Aronov-Pikus mechanism of spin relaxation for electrons.
- arXiv:2003.08214 [pdf]
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Title: Interface Bonding of Zr1-xAlxN Nanocomposites Investigated by X-ray Spectroscopies and First Principles CalculationsComments: 14 pages, 8 picturesJournal-ref: Physical Review RESEARCH 2, 013328 (2020)Subjects: Materials Science (cond-mat.mtrl-sci)
The electronic structure, chemical bonding and interface component in ZrN-AlN nanocomposites formed by phase separation during thin film deposition of metastable Zr1-xAlxN (x=0.0, 0.12, 0.26, 0.40) is investigated by resonant inelastic X-ray scattering/X-ray emission and X-ray absorption spectroscopy and compared to first-principles calculations including transitions between orbital angular momentum final states. The experimental spectra are compared with different interface-slab model systems using first-principle all electron full-potential calculations where the core states are treated fully relativistic. As shown in this work, the bulk sensitivity and element selectivity of X-ray spectroscopy enables to probe the symmetry and orbital directions at interfaces between cubic and hexagonal crystals. We show how the electronic structure develop from local octahedral bond symmetry of cubic ZrN that distorts for increasing Al content into more complex bonding. This results in three different kinds of bonding originating from semi-coherent interfaces with segregated ZrN and lamellar AlN nanocrystalline precipitates. An increasing chemical shift and charge transfer between the elements takes place with increasing Al content and affects the bond strength and increases resistivity.
- arXiv:2003.08226 [pdf, other]
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Title: Crossover from Fabry-Pérot to charging oscillations in correlated carbon nanotubesSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Strongly Correlated Electrons (cond-mat.str-el)
We report on electron transport measurements in high-quality carbon nanotube devices with a total transmission of about 1/2. At liquid helium temperature the linear conductance oscillates with moderate amplitude as a function of the gate voltage around an average value of the conductance quantum. Upon decreasing temperature, we observe an intriguing fourfold increase in the period of the oscillations accompanied by an enhancement in their amplitude. While the high-temperature oscillations are suggestive of charging effects in an open interacting quantum dot, the low-temperature transport characteristics is reminiscent of single-particle Fabry-P\'erot interference in a carbon nanotube waveguide. A similar crossover is observed in the low-temperature differential conductance by tuning the source-drain voltage. We reconcile these observations by attributing the four-fold increase at low energies to the interplay of interactions and quantum fluctuations, leading to a correlated Fabry-P\'erot regime.
- arXiv:2003.08227 [pdf, other]
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Title: Unusual Transport Phenomena in Spatially Modulated Correlated Electron WaveguidesSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Strongly Correlated Electrons (cond-mat.str-el)
Recent transport experiments in spatially modulated quasi-1D structures created on top of LaAlO$_3$/SrTiO$_3$ interfaces have revealed some unconventional features, including extraordinary phenomena conspicuously absent without the modulation. In this work, we focus on two of these remarkable features and provide theoretical analysis allowing their interpretation. The first one is the appearance of two-terminal conductance plateaus at rational fractions of $e^2/h$. We explain how this phenomenon, previously believed to be possible only in systems with strong repulsive interactions, can be stabilized in a system with attraction in the presence of the modulation. Using our theoretical framework we find the plateau amplitude and shape, and characterize the correlated phase which develops in the system due to the partial gap, namely a Luttinger liquid of electronic trions. The second peculiar observation is a sharp conductance dip below a conductance of $1\times e^2/h$, which continuously changes its value when tuning the system. We theorize it originates in an effective periodic spin-orbit field felt by the electrons leading to resonant backscattering. The behavior of this dip can be reliably accounted for by considering the finite length of the electronic waveguides, as well as the interactions therein. The phenomena discussed in this work exemplify the intricate interplay of strong interactions and spatial modulations, and reveal the potential for novel strongly correlated phases of matter in system which prominently feature both.
- arXiv:2003.08234 [pdf, other]
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Title: Designer flat bands in one-dimensional artificial systemsSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Certain lattices with specific geometries have one or more spectral bands that are strictly flat, i.e. the electron energy is independent of the momentum. This can occur robustly irrespective of the specific couplings between the lattices sites due to the lattice symmetry, or it can result from fine-tuned couplings between the lattice sites. While the theoretical picture behind flat electronic bands is well-developed, experimental realization of these lattices has proven challenging. Utilizing scanning tunnelling microscopy (STM) and spectroscopy (STS), we manipulate individual vacancies in a chlorine monolayer on Cu(100) to construct various atomically precise 1D lattices with engineered flat bands. We realize experimentally both gapped and gapless flat band systems with single or multiple flat bands. We also demonstrate tuneability of the energy of the flat bands and how they can be switched "on" and "off" by breaking and restoring the symmetry of the lattice geometry. The experimental findings are corroborated by tight-binding calculations. Our results constitute the first experimental realizations of engineered flat bands in a 1D solid-state system and pave the way towards the construction of e.g. topological flat band systems and experimental tests of flat-band-assisted superconductivity in a fully controlled system.
- arXiv:2003.08252 [pdf, other]
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Title: The Floquet Engineer's HandbookComments: This is a significantly expanded version of supplementary information originally included in arXiv:1909.02008, now upgraded to a stand-alone, living document. Suggestions for further sections are welcomeSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Quantum Gases (cond-mat.quant-gas); Quantum Physics (quant-ph)
We provide a pedagogical technical guide to many of the key theoretical tools and ideas that underlie work in the field of Floquet engineering. We hope that this document will serve as a useful resource for new researchers aiming to enter the field, as well as experienced researchers who wish to gain new insight into familiar or possibly unfamiliar methods. This guide was developed out of supplementary material as a companion to our recent review, "Band structure engineering and non-equilibrium dynamics in Floquet topological insulators," arXiv:1909.02008. The primary focus is on analytical techniques relevant for Floquet-Bloch band engineering and related many-body dynamics. We will continue to update this document over time to include additional content, and welcome suggestions for further topics to consider.
- arXiv:2003.08254 [pdf, ps, other]
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Title: Identities for correlation functions in classical statistical mechanics and the problem of crystal statesAuthors: David RuelleComments: 8 pagesSubjects: Statistical Mechanics (cond-mat.stat-mech); Mathematical Physics (math-ph)
Let $z$ be the activity of point particles described by classical equilibrium statistical mechanics in ${\bf R}^\nu$. The correlation functions $\rho^z(x_1,\dots,x_k)$ denote the probability densities of finding $k$ particles at $x_1,\dots,x_k$. Letting $\phi^z(x_1,\dots,x_k)$ be the cluster functions corresponding to the $\rho^z(x_1,\dots,x_k)/z^k$ we prove identities of the type $$ \phi^{z_0+z'}(x_1,\dots,x_k) $$ $$ =\sum_{n=0}^\infty{z'^n\over n!}\int dx_{k+1}\dots\int dx_{k+n}\,\phi^{z_0}(x_1,\dots,x_{k+n}) $$ It is then non-rigorously argued that, assuming a suitable cluster property (decay of correlations) for a crystal state, the pressure and the translation invariant correlation functions \- $\rho^z(x_1,\dots,x_k)$ are real analytic functions of $z$.
- arXiv:2003.08257 [pdf, other]
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Title: Quantum Hall phase emerging in an array of atoms interacting with photonsAuthors: Alexander V. Poshakinskiy, Janet Zhong, Yongguan Ke, Nikita A. Olekhno, Chaohong Lee, Yuri S. Kivshar, Alexander N. PoddubnyComments: 8 pages, 4 figures + supplementary materialsSubjects: Quantum Physics (quant-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Pattern Formation and Solitons (nlin.PS); Optics (physics.optics)
Topological quantum phases underpin many concepts of modern physics. While the existence of disorder-immune topological edge states of electrons usually requires magnetic fields, direct effects of magnetic field on light are very weak. As a result, demonstrations of topological states of photons employ synthetic fields engineered in special complex structures or external time-dependent modulations. Here, we reveal that the quantum Hall phase with topological edge states, spectral Landau levels and Hofstadter butterfly can emerge in a simple quantum system, where topological order arises solely from interactions without any fine-tuning. Such systems, arrays of two-level atoms (qubits) coupled to light being described by the classical Dicke model, have recently been realized in experiments with cold atoms and superconducting qubits. We believe that our finding will open new horizons in several disciplines including quantum physics, many-body physics, and nonlinear topological photonics, and it will set an important reference point for experiments on qubit arrays and quantum simulators.
- arXiv:2003.08258 [pdf]
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Title: Function follows form: From semiconducting to metallic towards superconducting PbS nanowires by faceting the crystalAuthors: Mohammad Mehdi Ramin Moayed, Sascha Kull, Angelique Rieckmann, Philip Beck, Michael Wagstaffe, Heshmat Noei, Andreas Kornowski, Ana B. Hungria, Rostyslav Lesyuk, Andreas Stierle, Christian KlinkeComments: 23 pages, 6 figuresJournal-ref: Adv. Func. Mater. 30 (2020) 1910503Subjects: Materials Science (cond-mat.mtrl-sci)
In the realm of colloidal nanostructures, with its immense capacity for shape and dimensionality control, the form is undoubtedly a driving factor for the tunability of optical and electrical properties in semiconducting or metallic materials. However, influencing the fundamental properties is still challenging and requires sophisticated surface or dimensionality manipulation. In this work, we present such a modification for the example of colloidal lead sulphide nanowires. We show that the electrical properties of lead sulphide nanostructures can be altered from semiconducting to metallic with indications of superconductivity, by exploiting the flexibility of the colloidal synthesis to sculpt the crystal and to form different surface facets. A particular morphology of lead sulphide nanowires has been synthesized through the formation of {111} surface facets, which shows metallic and superconducting properties in contrast to other forms of this semiconducting crystal, which contain other surface facets ({100} and {110}). This effect, which has been investigated with several experimental and theoretical approaches, is attributed to the presence of lead rich {111} facets. The insights promote new strategies for tuning the properties of crystals as well as new applications for lead sulphide nanostructures.
- arXiv:2003.08260 [pdf]
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Title: The 2D pn Junction Driven Out-of-EquilibriumSubjects: Applied Physics (physics.app-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Doped pn junctions are fundamental electrical components in modern electronics and optoelectronics. Due to the physical properties and unique structures of the two-dimensional (2D) materials, 2D pn junctions made of these novel materials may be considered as basic building blocks of more complex devices. In this work, we develop a comprehensive physics based simulator model to investigate the 2D lateral pn junction driven out-of-equilibrium based on the solution of the 2D Poissons equation coupled to the drift-diffusion and continuity equations. Notably, the simulator takes into account the strong influence of the out-of-plane electric field through the surrounding dielectric. Our study reveals that a Shockley-like equation for the ideal current-voltage characteristic, similar to that of the 3D pn junction, can be obtained for 2D pn junctions, provided an appropriate effective depletion layer is defined. The impact of recombination-generation processes inside the large depletion layer produces significant deviation from current-voltage (J-V) characteristics. Moreover, we analyze the depletion and diffusion capacitances of 2D lateral pn junction and discuss its cut-off frequency as the relevant Figure-of-Merit (FoM) for RF applications. To investigate the impact of the dimensionality in the performance of 2D junctions, we benchmark the MoS2 junction (2D case) against the Si junction (3D case).
- arXiv:2003.08261 [pdf]
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Title: Neutron diffraction and symmetry analysis of the martensitic transformation in Co-doped Ni$_2$MnGaJournal-ref: Phys. Rev. B 101, 094105 (2020)Subjects: Materials Science (cond-mat.mtrl-sci)
Martensitic transformations are strain driven displacive transitions governing the mechanical and physical properties in intermetallic materials. This is the case in Ni$_2$MnGa, where the martensite transition is at the heart of the striking magnetic shape memory and magneto-caloric properties. Interestingly, the martensitic transformation is preceded by a pre-martensite phase, and the role of this precursor and its influence on the martensitic transition and properties is still a matter of debate. In this work, we report on the influence of Co doping (Ni$_{50-x}$Co$_x$Mn$_{25}$Ga$_{25}$ with x = 3 and 5) on the martensitic transformation path in stoichiometric Ni$_2$MnGa by neutron diffraction. The use of the superspace formalism to describe the crystal structure of the modulated martensitic phases, joined with a group theoretical analysis allows unfolding the different distortions featuring the structural transitions. Finally, a general Landau thermodynamic potential of the martensitic transformation, based on the symmetry analysis is outlined. The combined use of phenomenological and crystallographic studies highlights the close relationship between the lattice distortions at the core of the Ni$_2$MnGa physical properties and, more in general, on the properties of the martensitic transformations in the Ni-Mn based Heusler systems.
- arXiv:2003.08279 [pdf, other]
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Title: Shortcuts to Adiabatic Pumping in Classical Stochastic SystemsComments: 6 pages, 2 figures, accepted for publication in Phys. Rev. LettJournal-ref: Phys. Rev. Lett. 124, 150603 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Statistical Mechanics (cond-mat.stat-mech)
Adiabatic pumping is characterized by a geometric contribution to the pumped charge, which can be non-zero even in the absence of a bias. However, as the driving speed is increased, non-adiabatic excitations gradually reduce the pumped charge, thereby limiting the maximal applicable driving frequencies. To circumvent this problem, we here extend the concept of shortcuts to adiabaticity to construct a control protocol which enables geometric pumping well beyond the adiabatic regime. Our protocol allows for an increase, by more than an order of magnitude, in the driving frequencies, and the method is also robust against moderate fluctuations of the control field. We provide a geometric interpretation of the control protocol and analyze the thermodynamic cost of implementing it. Our findings can be realized using current technology and potentially enable fast pumping of charge or heat in quantum dots, as well as in other stochastic systems from physics, chemistry, and biology.
- arXiv:2003.08294 [pdf]
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Title: Functionalized MXenes as Effective Polyselenides Immobilizer for Lithium-Selenium Batteries: A Density Functional Theory (DFT) StudySubjects: Materials Science (cond-mat.mtrl-sci)
The practical applications of lithium selenium (Li-Se) batteries are impeded primarily due to the dissolution and migration of higher order polyselenides (Li2Sen) into the electrolyte (known as shuttle effect) and inactive deposition of lower order polyselenides. The high electrical conductivity and mechanical strengths of MXenes make them a suitable candidate to provide adequate anchoring to prevent polyselenides dissolution and improved electrochemical performance. Herein, we used density functional theory (DFT) calculations to understand the binding mechanism of Li2Sen on graphene and surface functionalized Ti3C2 MXenes. We used graphene as reference material to assess Li2Sen binding strengths on functionalized Ti3C2X2 (where X = S, O, F, and Cl). We observed that Ti3C2S2 and Ti3C2O2 exhibit superior anchoring behavior compared to graphene, Ti3C2F2, and Ti3C2Cl2. The calculated Li2Sen adsorption strength provided by S and O terminated Ti3C2 are stronger than the commonly used ether-based electrolyte, which is a requisite for effective suppression of the Li2Sen shuttling. The adsorbed Li2Sen on Ti3C2X2 and graphene retains their structural integrity without a chemical decomposition. The density of states (DOS) analysis exhibits that the conductive behavior of the Ti3C2X2 is preserved even after Li2Sen adsorption, which can stimulate the electrochemical activity of involved Li2Sen chemistry. Based on our unprecedented results, Ti3C2S2 and Ti3C2O2 are found to exhibit superior anchoring behavior for Li2Sen adsorption, which can be leveraged for designing effective selenium-based cathode materials to boost the electrochemical performance of the Li-Se battery system
- arXiv:2003.08296 [pdf]
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Title: Suspended graphene membranes with attached silicon proof masses as piezoresistive NEMS accelerometersAuthors: Xuge Fan (1), Fredrik Forsberg (4), Anderson D. Smith (3), Stephan Schröder (1), Stefan Wagner (2), Mikael Östling (3), Max C. Lemme (2, 3), Frank Niklaus (1) ((1) Department of Micro and Nanosystems, KTH Royal Institute of Technology, (2) Faculty of Electrical Engineering and Information Technology, RWTH Aachen University, (3) Department of Integrated Devices and Circuits, KTH Royal Institute of Technology, (4) Scania Tekniskt Centrum)Comments: 40 pages, 5 figures. arXiv admin note: text overlap with arXiv:2003.07115Journal-ref: Nano Lett.19 10 (2019) 6788-6799Subjects: Applied Physics (physics.app-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Graphene is an atomically thin material that features unique electrical and mechanical properties, which makes it an extremely promising material for future nanoelectromechanical systems (NEMS). Recently, basic NEMS accelerometer functionality has been demonstrated by utilizing piezoresistive graphene ribbons with suspended silicon proof masses. However, the proposed graphene ribbons have limitations regarding mechanical robustness, manufacturing yield and the maximum measurement current that can be applied across the ribbons. Here, we report on suspended graphene membranes that are fully-clamped at their circumference and that have attached silicon proof masses. We demonstrate their utility as piezoresistive NEMS accelerometers and they are found to be more robust, have longer life span and higher manufacturing yield, can withstand higher measurement currents and are able to suspend larger silicon proof masses, as compared to the previously graphene ribbon devices. These findings are an important step towards bringing ultra-miniaturized piezoresistive graphene NEMS closer towards deployment in emerging applications such as in wearable electronics, biomedical implants and internet of things (IoT) devices.
- arXiv:2003.08299 [pdf, other]
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Title: Accessing different topological classes and types of Majorana edge states in coupled superconducting platforms using perturbationsComments: 14 pages, 6 figures. Some related aspects of this work can be found in the PhD thesis of S, Ray at arxiv:1803.05960Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Strongly Correlated Electrons (cond-mat.str-el); Superconductivity (cond-mat.supr-con)
The study of topological classes and their associated edge states has been of ongoing interest. In one dimension, the standard platform of these studies has been the conventional Kitaev wire and its realizations. In this work, we study the edge states in coupled p-wave platforms in 1D, in the presence of experimentally relevant perturbations, like a Zeeman field and s-wave SC. Firstly, we show that the unperturbed coupled p-wave setup by itself can have two types of Majorana edge states, depending on the value of the effective onsite potential. We show that additional components like Zeeman field and s-wave term can cause transitions to different symmetry classes, both topologically trivial or non-trivial, and change the nature of these edge states. In the presence of the perturbations, we show that there are 3 symmetry classes when the effective p-wave pairing is equal between the spin species, and 6 for the second kind, when the pairing differs by a phase $\pi$ between the two. Some of these classes are topologically non-trivial. Further, we explore the nature of subgap states when we have a junction between two such topological setups and their corresponding behaviour with the phase of the p-wave order parameter. Our work provides a theoretical framework of the different ways to get non-trivial topological classes in coupled p-wave nanowire setup, using experimentally feasible perturbations, and the nature of subgap states across junctions of these platforms.
- arXiv:2003.08307 [pdf]
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Title: Non-equilibrium thermodynamics with first-passage time of states as independent thermodynamic parameterAuthors: V. V. RyazanovComments: 21 pages, 0 figures. arXiv admin note: substantial text overlap with arXiv:1910.05128Subjects: Statistical Mechanics (cond-mat.stat-mech)
Non-equilibrium states of a thermodynamic statistical system are investigated using the thermodynamic parameter of the system lifetime, first-passage time, the time before degeneration of the system under influence of fluctuations. Statistical distributions that describe the behavior of energy and lifetime are used. Entropy and obtained thermodynamic relations are compared with the results of Extended Irreversible thermodynamics, where as an additional parameter selected fluxes. Explicit expressions are obtained for average lifetime and conjugate thermodynamic quantity. It is shown that, when is only one stationary non-equilibrium state and exponential distribution for the lifetime, flows can only reduce the average system lifetime. However, there are possibilities to description of increase the average lifetime of the system. A description of the growth of the average lifetime for one stationary non-equilibrium state is possible when choosing distributions for the lifetime, differing from the limiting exponential distribution.
- arXiv:2003.08309 [pdf, other]
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Title: Molecular interpretation of the non-Newtonian viscoelastic behavior of liquid water at high frequenciesComments: Supplemental material is provided as ancillary fileSubjects: Fluid Dynamics (physics.flu-dyn); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Soft Condensed Matter (cond-mat.soft); Statistical Mechanics (cond-mat.stat-mech); Chemical Physics (physics.chem-ph)
Using classical as well as ab-initio molecular dynamics simulations, we calculate the frequency-dependent shear viscosity of pure water and water-glycerol mixtures. In agreement with recent experiments, we find deviations from Newtonian-fluid behavior in the THz regime. Based on an extension of the Maxwell model, we introduce a viscoelastic model to describe the observed viscosity spectrum of pure water. We find four relaxation modes in the spectrum which we attribute to i) hydrogen-bond network topology changes, ii) hydrogen-bond stretch vibrations of water pairs, iii) collective vibrations of water molecule triplets, and iv) librational excitations of individual water molecules. Our model quantitatively describes the viscoelastic response of liquid water on short timescales, where the hydrodynamic description via a Newtonian-fluid model breaks down.
- arXiv:2003.08315 [pdf, other]
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Title: The AiiDA-KKR plugin and its application to high-throughput impurity embedding into a topological insulatorSubjects: Materials Science (cond-mat.mtrl-sci); Computational Physics (physics.comp-ph)
The ever increasing availability of supercomputing resources led computer-based materials science into a new era of high-throughput calculations. Recently, Pizzi et al. [Comp. Mat. Sci. 111, 218 (2016)] introduced the AiiDA framework that provides a way to automate calculations while allowing to store the full provenance of complex workflows in a database. We present the development of the AiiDA-KKR plugin that allows to perform a large number of ab initio impurity embedding calculations based on the relativistic full-potential Korringa-Kohn-Rostoker Green function method. The capabilities of the AiiDA-KKR plugin are demonstrated with the calculation of several thousand impurities embedded into the prototypical topological insulator Sb2Te3. The results are collected in the JuDiT database which we use to investigate chemical trends as well as Fermi level and layer dependence of physical properties of impurities. This includes the study of spin moments, the impurity's tendency to form in-gap states or its effect on the charge doping of the host-crystal. These properties depend on the detailed electronic structure of the impurity embedded into the host crystal which highlights the need for ab initio calculations in order to get accurate predictions.
- arXiv:2003.08341 [pdf]
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Title: Ultrafast formation of transient 2D diamond-like structure in twisted bilayer grapheneAuthors: Duan Luo, Dandan Hui, Bin Wen, Renkai Li, Jie Yang, Xiaozhe Shen, Alex Hume Reid, Stephen Weathersby, Michael E. Kozina, Suji Park, Yang Ren, Troy D. Loeffler, S. K. R. S. Sankaranarayanan, Maria K. Y. Chan, Xing Wang, Jinshou Tian, Ilke Arslan, Xijie Wang, Tijana Rajh, Jianguo WenSubjects: Materials Science (cond-mat.mtrl-sci)
Due to the absence of matching carbon atoms at honeycomb centers with carbon atoms in adjacent graphene sheets, theorists predicted that a sliding process is needed to form AA, AB, or ABC stacking when directly converting graphite into sp3 bonded diamond. Here, using twisted bilayer graphene, which naturally provides AA and AB stacking configurations, we report the ultrafast formation of a transient 2D diamond-like structure (which is not observed in aligned graphene) under femtosecond laser irradiation. This photo-induced phase transition is evidenced by the appearance of new bond lengths of 1.94A and 3.14A in the time-dependent differential pair distribution function using MeV ultrafast electron diffraction. Molecular dynamics and first principles calculation indicate that sp3 bonds nucleate at AA and AB stacked areas in moire pattern. This work sheds light on the direct graphite-to-diamond transformation mechanism, which has not been fully understood for more than 60 years.
- arXiv:2003.08346 [pdf, other]
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Title: Magnetic structures, spin-flop transition and coupling of Eu and Mn magnetism in the Dirac semimetal EuMnBi$_2$Authors: Fengfeng Zhu, Xiao Wang, Martin Meven, Junda Song, Thomas Mueller, Changjiang Yi, Wenhai Ji, Youguo Shi, Jie Ma, Karin Schmalzl, Wolfgang F. Schmidt, Yixi Su, Thomas BrückelComments: 12 pages, 11 figuresSubjects: Strongly Correlated Electrons (cond-mat.str-el); Materials Science (cond-mat.mtrl-sci)
We report here a comprehensive study of the AFM structures of the Eu and Mn magnetic sublattices as well as the interplay between Eu and Mn magnetism in this compound by using both polarized and non-polarized single-crystal neutron diffraction. Magnetic susceptibility, specific heat capacity measurements and the temperature dependence of magnetic diffractions suggest that the AFM ordering temperature of the Eu and Mn moments is at 22 and 337 K, respectively. The magnetic moments of both Eu and Mn ions are oriented along the crystallographic $c$ axis, and the respective magnetic propagation vector is $\textbf{k}_{Eu} = (0,0,1)$ and $\textbf{k}_{Mn}=(0,0,0)$. With proper neutron absorption correction, the ordered moments are refined at 3 K as 7.7(1) $\mu_B$ and 4.1(1) $\mu_B$ for the Eu and Mn ions, respectively. In addition, a spin-flop (SF) phase transition of the Eu moments in an applied magnetic field along the $c$ axis was confirmed to take place at a critical field of B$_c$ $\sim$ 5.3 T. The evolution of the Eu magnetic moment direction as a function of the applied magnetic field in the SF phase was also determined. Clear kinks in both field and temperature dependence of the magnetic reflections ($\pm1$, 0, 1) of Mn were observed at the onset of the SF phase transition and the AFM order of the Eu moments, respectively. This unambiguously indicates the existence of a strong coupling between Eu and Mn magnetism. The interplay between two magnetic sublattices could bring new possibilities to tune Dirac fermions via changing magnetic structures by applied fields in this class of magnetic topological semimetals.
- arXiv:2003.08368 [pdf, other]
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Title: Phases of the (2+1) dimensional SO(5) non-linear sigma model with topological termSubjects: Strongly Correlated Electrons (cond-mat.str-el)
We use the half-filled zeroth Landau level in graphene as a regularization scheme to study the physics of the SO(5) non-linear sigma model subject to a Wess-Zumino-Witten topological term in 2+1 dimensions. As shown by Ippoliti et al. [PRB 98, 235108 (2019)], this approach allows for negative sign free auxiliary field quantum Monte Carlo simulations. The model has a single free parameter, $U_0$, that monitors the stiffness. Within the parameter range accessible to negative sign free simulations, we observe an ordered phase in the large $U_0$ or stiff limit. Remarkably, upon reducing $U_0$ the magnetization drops substantially, and the correlation length exceeds our biggest system sizes, accommodating 100 flux quanta. The implications of our results for deconfined quantum phase transitions between valence bond solids and anti-ferromagnets are discussed.
- arXiv:2003.08369 [pdf, other]
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Title: Zero-bias crossings and peculiar Shapiro maps in graphene Josephson junctionsAuthors: T. F. Q. Larson, L. Zhao, E. G. Arnault, M. T. Wei, A. Seredinski, H. Li, K. Watanabe, T. Taniguchi, F. Amet, G. FinkelsteinComments: Main: 5 Pages + 4 Figures, Supplementary: 3 Pages + 3 FiguresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Chaotic Dynamics (nlin.CD)
The AC Josephson effect manifests itself in the form of "Shapiro steps" of quantized voltage in Josephson junctions subject to RF radiation. This effect presents an early example of a driven-dissipative quantum phenomenon and is presently utilized in primary voltage standards. Shapiro steps have also become one of the standard tools to probe junctions made in a variety of novel materials. Here, we study Shapiro steps in a widely tunable graphene-based Josephson junction. We investigate the variety of patterns that can be obtained in this well-understood system depending on the carrier density, temperature, RF frequency, and magnetic field. Although the patterns of Shapiro steps can change drastically when just one parameter is varied, the overall trends can be understood and the behaviors straightforwardly simulated. The resulting understanding may help in interpreting similar measurements in more complex materials.
Replacements
- arXiv:1610.06520 (replaced) [pdf, other]
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Title: High-frequency asymptotics of the vertex function: diagrammatic parametrization and algorithmic implementationAuthors: N. Wentzell, G. Li, A. Tagliavini, C. Taranto, G. Rohringer, K. Held, A. Toschi, S. AndergassenComments: 25 pages, 25 figuresSubjects: Strongly Correlated Electrons (cond-mat.str-el)
Vertex functions are a crucial ingredient of several forefront many-body algorithms in condensed matter physics. However, the full treatment of their frequency and momentum dependence severely restricts numerical calculations. A significant advancement requires an efficient treatment of the high-frequency asymptotic behavior of the vertex functions. In this work, we first provide a detailed diagrammatic analysis of the high-frequency structures and their physical interpretation. Based on these insights, we propose a parametrization scheme, which captures the whole high-frequency domain for arbitrary values of the Coulomb interaction and electronic density, and we discuss the details of its algorithmic implementation in many-body solvers based on parquet-equations as well as functional renormalization group schemes. Finally, we assess its validity by comparing our results for a single impurity Anderson model with exact diagonalization calculations. The proposed parametrization is pivotal for the algorithmic development of all quantum many-body methods based on vertex functions arising from both local and non-local microscopic interactions, such as the diagrammatic approaches including spatial correlations beyond dynamical mean-field theory.
- arXiv:1711.04302 (replaced) [pdf, ps, other]
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Title: Lattice vibrations in the harmonic approximationSubjects: Materials Science (cond-mat.mtrl-sci); Strongly Correlated Electrons (cond-mat.str-el); Mathematical Physics (math-ph); Quantum Physics (quant-ph)
We present some theoretical results on the lattice vibrations that are necessary for a concise derivation of the Debye-Waller factor in the harmonic approximation. First we obtain an expression for displacement of an atom in a crystal lattice from its equilibrium position. Then we show that an atomic displacement has the Gaussian distribution. Finally, we obtain the computational formula for the Debye-Waller factor in the Debye model.
- arXiv:1806.00594 (replaced) [pdf, ps, other]
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Title: Studies of non-trivial band topology and electron-hole compensation in YSbComments: 6 pages, 5 figuresSubjects: Materials Science (cond-mat.mtrl-sci)
In this article, we study non-trivial topological phase and electron-hole compensation in extremely large magnetoresistance (XMR) material YSb under hydrostatic pressure using first-principles calculations. YSb is topologically trivial at ambient pressure, but undergoes a reentrant topological phase transition under hydrostatic pressure. The reentrant behavior of topological quantum phase is then studied as a function of charge density ratio under pressure. From the detailed investigation of Fermi surfaces, it is found that electron to hole densities ratio increases with pressure, however a non-trivial topological phase appears without perfect electron-hole compensation. The results indicate that the non-trivial topological phase under hydrostatic pressure may not have maximal influence on the magnetoresistance, and need further investigations through experiments to determine the exact relationship between topology and XMR effect.
- arXiv:1812.02144 (replaced) [pdf, other]
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Title: Rapid mixing of path integral Monte Carlo for 1D stoquastic HamiltoniansComments: 23 pages, 2 figuresSubjects: Quantum Physics (quant-ph); Statistical Mechanics (cond-mat.stat-mech); Data Structures and Algorithms (cs.DS)
Path integral quantum Monte Carlo (PIMC) is a method for estimating thermal equilibrium properties of stoquastic quantum spin systems by sampling from a classical Gibbs distribution using Markov chain Monte Carlo. The PIMC method has been widely used to study the physics of materials and for simulated quantum annealing, but these successful applications are rarely accompanied by formal proofs that the Markov chains underlying PIMC rapidly converge to the desired equilibrium distribution. In this work we analyze the mixing time of PIMC for 1D stoquastic Hamiltonians, including disordered transverse Ising models (TIM) with long-range algebraically decaying interactions as well as disordered XY spin chains with nearest-neighbor interactions. By bounding the convergence time to the equilibrium distribution we rigorously justify the use of PIMC to approximate partition functions and expectations of observables for these models at inverse temperatures that scale at most logarithmically with the number of qubits. The mixing time analysis is based on the canonical paths method applied to the single-site Metropolis Markov chain for the Gibbs distribution of 2D classical spin models with couplings related to the interactions in the quantum Hamiltonian. Since the system has strongly nonisotropic couplings that grow with system size, it does not fall into the known cases where 2D classical spin models are known to mix rapidly.
- arXiv:1812.10257 (replaced) [pdf, ps, other]
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Title: Intrinsic quantum dynamics and its measurement through local-in-position weak valuesSubjects: Quantum Physics (quant-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Due to quantum backaction, generalized positive-operator valued measurements without post-selection happen to be invasive for superposition states. This precludes a clear-cut definition of intrinsic (i.e. measurement-independent) dynamical properties such as, for example, a coherent quantum work.On the contrary, certain weak values, i.e., including a particular post-selction rule, are, by construction, free from quantum backaction effects and hence provide apparatus-independent information. In this work we will prove the existence of a one-to-one correspondence between any local-in-position weak value and the intrinsic Bohmian property associated to the corresponding observable. Therefore, intrinsic Bohmian properties, independent of the measuring apparatus by definition and measurable through local-in-position weak values, can be understood as a genuine representation of the unperturbed/intrinsic dynamics of coherent quantum systems.The dwell time, the work distribution and the high-frequency electrical current defined for quantum systems are shown to be paradigmatic examples of the physical soundness of intrinsic Bohmian properties.
- arXiv:1902.00507 (replaced) [pdf, other]
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Title: Higher-order topological insulators in amorphous solidsComments: 6 Pages, 5 Figures: Published version (Supplemental Materials as ancillary file)Journal-ref: Phys. Rev. Research 2, 012067 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Disordered Systems and Neural Networks (cond-mat.dis-nn)
We identify the possibility of realizing higher order topological (HOT) phases in noncrystalline or amorphous materials. Starting from two and three dimensional crystalline HOT insulators, accommodating topological corner states, we gradually enhance structural randomness in the system. Within a parameter regime, as long as amorphousness is confined by outer crystalline boundary, the system continues to host corner states, yielding amorphous HOT insulators. However, as structural disorder percolates to the edges, corner states start to dissolve into amorphous bulk, and ultimately the system becomes a trivial insulator when amorphousness plagues the entire system. These outcomes are further substantiated by computing the quadrupolar (octupolar) moment in two (three) dimensions. Therefore, HOT phases can be realized in amorphous solids, when wrapped by a thin (lithographically grown, for example) crystalline layer. Our findings suggest that crystalline topological phases can be realized even in the absence of local crystalline symmetry.
- arXiv:1903.01664 (replaced) [pdf]
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Title: Polar Coupling Enabled Nonlinear Optical Filtering at MoS$_2$/Ferroelectric HeterointerfacesAuthors: Dawei Li, Xi Huang, Zhiyong Xiao, Hanying Chen, Le Zhang, Yifei Hao, Jingfeng Song, Ding-Fu Shao, Evgeny Y. Tsymbal, Yongfeng Lu, Xia HongComments: 22 pages, 4 figuresJournal-ref: Nature Communications 11, 1422 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci)
Complex oxide heterointerfaces and van der Waals heterostructures present two versatile but intrinsically different platforms for exploring emergent quantum phenomena and designing new functionalities. The rich opportunity offered by the synergy between these two classes of materials, however, is yet to be charted. Here, we report an unconventional nonlinear optical filtering effect resulting from the interfacial polar alignment between monolayer MoS$_2$ and a neighboring ferroelectric oxide thin film. The second harmonic generation response at the heterointerface is either substantially enhanced or almost entirely quenched by an underlying ferroelectric domain wall depending on its chirality, and can be further tailored by the polar domains. Unlike the extensively studied coupling mechanisms driven by charge, spin, and lattice, the interfacial tailoring effect is solely mediated by the polar symmetry, as well explained via our density functional theory calculations, pointing to a new material strategy for the functional design of nanoscale reconfigurable optical applications.
- arXiv:1903.09439 (replaced) [pdf, ps, other]
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Title: Mathematical open problems in Projected Entangled Pair StatesComments: Notes associated to the Santal\'o Lecture 2017, Universidad Complutense de Madrid (UCM), minor typos correctedJournal-ref: Revista Matem\'atica Complutense 32, Issue 3 (2019)Subjects: Mathematical Physics (math-ph); Strongly Correlated Electrons (cond-mat.str-el); Quantum Physics (quant-ph)
Projected Entangled Pair States (PEPS) are used in practice as an efficient parametrization of the set of ground states of quantum many body systems. The aim of this paper is to present, for a broad mathematical audience, some mathematical questions about PEPS.
- arXiv:1903.11852 (replaced) [pdf, ps, other]
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Title: TKNN formula for general HamiltonianComments: revised version, 23 pagesJournal-ref: Phys. Rev. D 101, 074507 (2020)Subjects: High Energy Physics - Theory (hep-th); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); High Energy Physics - Lattice (hep-lat)
Topological insulators in odd dimensions are characterized by topological numbers. We prove the well-known relation between the topological number given by the Chern character of the Berry curvature and the Chern-Simons level of the low energy effective action for a general class of Hamiltonians bilinear in the fermion with general U(1) gauge interactions including non-minimal couplings by an explicit calculation. A series of Ward-Takahashi identities are crucial to relate the Chern-Simons level to a winding number, which could then be directly reduced to Chern character of Berry curvature by carrying out the integral over the temporal momenta.
- arXiv:1905.09912 (replaced) [pdf, other]
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Title: Stochastic Yield Catastrophes and Robustness in Self-AssemblySubjects: Biological Physics (physics.bio-ph); Soft Condensed Matter (cond-mat.soft); Subcellular Processes (q-bio.SC)
A guiding principle in self-assembly is that, for high production yield, nucleation of structures must be significantly slower than their growth. However, details of the mechanism that impedes nucleation are broadly considered irrelevant. Here, we analyze self-assembly into finite-sized target structures employing mathematical modeling. We investigate two key scenarios to delay nucleation: (i) by introducing a slow activation step for the assembling constituents and, (ii) by decreasing the dimerization rate. These scenarios have widely different characteristics. While the dimerization scenario exhibits robust behavior, the activation scenario is highly sensitive to demographic fluctuations. These demographic fluctuations ultimately disfavor growth compared to nucleation and can suppress yield completely. The occurrence of this stochastic yield catastrophe does not depend on model details but is generic as soon as number fluctuations between constituents are taken into account. On a broader perspective, our results reveal that stochasticity is an important limiting factor for self-assembly and that the specific implementation of the nucleation process plays a significant role in determining the yield.
- arXiv:1905.13337 (replaced) [pdf, other]
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Title: Spin and charge correlations across the metal-to-insulator crossover in the half-filled $2d$ Hubbard modelComments: 6 pages, 5 figures, published versionJournal-ref: Phys. Rev. Lett. 124, 117602 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el); Quantum Gases (cond-mat.quant-gas)
The $2d$ Hubbard model with nearest-neighbour hopping on the square lattice and an average of one electron per site is known to undergo an extended crossover from metallic to insulating behavior driven by proliferating antiferromagnetic correlations. We study signatures of this crossover in spin and charge correlation functions and present results obtained with controlled accuracy using diagrammatic Monte Carlo in the range of parameters amenable to experimental verification with ultracold atoms in optical lattices. The qualitative changes in charge and spin correlations associated with the crossover are observed at well-separated temperature scales, which encase the intermediary regime of non-Fermi-liquid character, where local magnetic moments are formed and non-local fluctuations in both channels are essential.
- arXiv:1906.02752 (replaced) [pdf, other]
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Title: Fractional disclination charge in two-dimensional $C_n-$symmetric topological crystalline insulatorsComments: 14+6 pages, 5 figures in main text, 6 figures in appendicesJournal-ref: Phys. Rev. B 101, 115115 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Strongly Correlated Electrons (cond-mat.str-el)
Robust fractional charge localized at disclination defects has been recently found as a topological response in $C_{6}$ symmetric 2D topological crystalline insulators (TCIs). In this article, we thoroughly investigate the fractional charge on disclinations in $C_n$ symmetric TCIs, with or without time reversal symmetry, and including spinless and spin-$\frac{1}{2}$ cases. We compute the fractional disclination charges from the Wannier representations in real space and use band representation theory to construct topological indices of the fractional disclination charge for all $2D$ TCIs that admit a (generalized) Wannier representation. We find the disclination charge is fractionalized in units of $\frac{e}{n}$ for $C_n$ symmetric TCIs; and for spin-$\frac{1}{2}$ TCIs, with additional time reversal symmetry, the disclination charge is fractionalized in units of $\frac{2e}{n}$. We furthermore prove that with electron-electron interactions that preserve the $C_n$ symmetry and many-body bulk gap, though we can deform a TCI into another which is topologically distinct in the free fermion case, the fractional disclination charge determined by our topological indices will not change in this process. Moreover, we use an algebraic technique to generalize the indices for TCIs with non-zero Chern numbers, where a Wannier representation is not applicable. With the inclusion of the Chern number, our generalized fractional disclination indices apply for all $C_n$ symmetric TCIs. Finally, we briefly discuss the connection between the Chern number dependence of our generalized indices and the Wen-Zee term.
- arXiv:1906.05755 (replaced) [pdf, ps, other]
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Title: Dirac Fermions in Antiferromagnetic FeSn Kagome Lattices with Combined Space Inversion and Time Reversal SymmetryAuthors: Zhiyong Lin, Chongze Wang, Pengdong Wang, Seho Yi, Lin Li, Qiang Zhang, Yifan Wang, Zhongyi Wang, Hao Huang, Yan Sun, Yaobo Huang, Dawei Shen, Donglai Feng, Zhe Sun, Jun-Hyung Cho, Changgan Zeng, Zhenyu ZhangComments: 6 pages, 4 figuresSubjects: Materials Science (cond-mat.mtrl-sci); Other Condensed Matter (cond-mat.other)
Symmetry principles play a critical role in formulating the fundamental laws of nature, with a large number of symmetry-protected topological states identified in recent studies of quantum materials. As compelling examples, massless Dirac fermions are jointly protected by the space inversion symmetry $P$ and time reversal symmetry $T$ supplemented by additional crystalline symmetry, while evolving into Weyl fermions when either $P$ or $T$ is broken. Here, based on first-principles calculations, we reveal that massless Dirac fermions are present in a layered FeSn crystal containing antiferromagnetically coupled ferromagnetic Fe kagome layers, where each of the $P$ and $T$ symmetries is individually broken but the combined $PT$ symmetry is preserved. These stable Dirac fermions protected by the combined $PT$ symmetry with additional non-symmorphic $S_{\rm{2z}}$ symmetry can be transformed to either massless/massive Weyl or massive Dirac fermions by breaking the $PT$ or $S_{\rm{2z}}$ symmetry. Our angle-resolved photoemission spectroscopy experiments indeed observed the Dirac states in the bulk and two-dimensional Weyl-like states at the surface. The present study substantially enriches our fundamental understanding of the intricate connections between symmetries and topologies of matter, especially with the spin degree of freedom playing a vital role.
- arXiv:1909.00778 (replaced) [pdf, ps, other]
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Title: Berry's Phase and Renormalization of Applied Oscillating Electric Fields by Topological Quasi-ParticlesAuthors: Godwill Mbiti KanyoloComments: 5 pages, 1 figure. Submitted in Physical Review ASubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We introduce the concept of Berry's phase in Josephson junctions and consider how this geometric phase arises due to applied oscillating electric fields. The electromagnetic field excites topological quasi-particles from the junction vacuum which affect Cooper-pair tunneling across the Josephson junction barrier. A finite Berry's phase can be detected by its renormalization of the electric field amplitude absorbed by the junction. This has implications for the designing of accurate Josephson junction microwave detectors.
- arXiv:1909.00961 (replaced) [pdf, ps, other]
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Title: Boltzmann entropy for quantum field systemsAuthors: Kyo YoshidaJournal-ref: Phys. Rev. A 101, 032110 (2020)Subjects: Statistical Mechanics (cond-mat.stat-mech); Quantum Physics (quant-ph)
A way to construct Boltzmann entropy, i.e., the entropy as a function of a microscopic pure state, for quantum field systems is proposed. Operators that shift the field in wavevector space are used in the construction. By employing an assumption, it is shown that, for almost all states in the ensemble of pure states corresponding to a thermodynamic state, the value of the proposed Boltzmann entropy coincides with that of the thermodynamic entropy for the thermodynamic state. For general self-interacting fields, the Boltzmann entropy evolves with time under Hamiltonian dynamics, so that it is capable of characterizing the thermalization of isolated quantum field systems.
- arXiv:1909.12532 (replaced) [pdf, other]
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Title: Prominent Cooper Pairing Away From the Fermi Level and its Spectroscopic Signature in Twisted Bilayer GrapheneComments: 6 pages + supplemental materialJournal-ref: Phys. Rev. Research 2, 012066 (2020)Subjects: Superconductivity (cond-mat.supr-con); Strongly Correlated Electrons (cond-mat.str-el)
We investigate phonon-mediated Cooper pairing in flat electronic band systems by solving the full-bandwidth multiband Eliashberg equations for superconductivity in magic angle twisted bilayer graphene using a realistic tight-binding model. We find that Cooper pairing away from the Fermi level contributes decisively to superconductivity by enhancing the critical temperature and ensures a robust finite superfluid density. We show that this pairing yields particle-hole asymmetric superconducting domes in the temperature-gating phase diagram and gives rise to distinct spectroscopic signatures in the superconducting state. We predict several such features in tunneling and angle resolved photoemission spectra for future experiments.
- arXiv:1909.13515 (replaced) [pdf]
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Title: Visualization of local magnetic moments emerging from impurities in the Hund's metal states of FeSeComments: 35 pages including main text and supplemental materialJournal-ref: Phys. Rev. Lett. 124, 117001 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el); Superconductivity (cond-mat.supr-con)
Understanding the origin of the magnetism of high temperature superconductors is crucial for establishing their unconventional pairing mechanism. Recently, theory predicts that FeSe is close to a magnetic quantum critical point, and thus weak perturbations such as impurities could induce local magnetic moments. To elucidate such quantum instability, we have employed scanning tunneling microscopy and spectroscopy. In particular, we have grown FeSe film on superconducting Pb(111) using molecular beam epitaxy and investigated magnetic excitation caused by impurities in the proximity-induced superconducting gap of FeSe. Our study provides a deep insight into the origin of the magnetic ordering of FeSe by showing the way local magnetic moments develop in response to impurities near the magnetic quantum critical point.
- arXiv:1910.00344 (replaced) [pdf]
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Title: Superfluid currents in half-moon polariton condensatesAuthors: E. S. Sedov, V. A. Lukoshkin, V. K. Kalevich, Z. Hatzopoulos, P. G. Savvidis, A. V. KavokinSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We excite exciton-polariton condensates in half-moon shapes by the non-resonant optical excitation of GaAs-based cylindrical pillar microcavities. In this geometry, the {\pi}-jump of the phase of the condensate wave function coexists with a gradual {\pm \pi} phase variation between two horns of the half-moon. We switch between clockwise and counter-clockwise phase currents by slightly shifting the excitation spot on the surface of the pillar. Half-moon condensates are expected to reveal features of two-level quantum systems similar to superconducting flux qubits
- arXiv:1910.00570 (replaced) [pdf, other]
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Title: Quantum Generalized HydrodynamicsComments: v1: 6+6 pages, 2 figures. v2: Accepted version; 6+6 pages, 2 figures. Substantial modifications: numerical checks are now presented for the interacting Lieb-Liniger model; previous checks for non-interacting fermions have been removed and will be published in a separate paperJournal-ref: Phys. Rev. Lett. 124, 140603 (2020)Subjects: Quantum Gases (cond-mat.quant-gas); Statistical Mechanics (cond-mat.stat-mech); Strongly Correlated Electrons (cond-mat.str-el)
Physical systems made of many interacting quantum particles can often be described by Euler hydrodynamic equations in the limit of long wavelengths and low frequencies. Recently such a classical hydrodynamic framework, now dubbed Generalized Hydrodynamics (GHD), was found for quantum integrable models in one spatial dimension. Despite its great predictive power, GHD, like any Euler hydrodynamic equation, misses important quantum effects, such as quantum fluctuations leading to non-zero equal-time correlations between fluid cells at different positions. Focusing on the one-dimensional gas of bosons with delta repulsion, and on states of zero entropy, for which quantum fluctuations are larger, we reconstruct such quantum effects by quantizing GHD. The resulting theory of quantum GHD can be viewed as a multi-component Luttinger liquid theory, with a small set of effective parameters that are fixed by the Thermodynamic Bethe Ansatz. It describes quantum fluctuations of truly nonequilibrium systems where conventional Luttinger liquid theory fails.
- arXiv:1910.03372 (replaced) [pdf, other]
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Title: The free energy of the two-dimensional dilute Bose gas. I. Lower boundComments: 61 pages, 1 figure; final version, to appear in Forum of Mathematics, SigmaSubjects: Mathematical Physics (math-ph); Quantum Gases (cond-mat.quant-gas); Statistical Mechanics (cond-mat.stat-mech)
We prove a lower bound for the free energy (per unit volume) of the two-dimensional Bose gas in the thermodynamic limit. We show that the free energy at density $\rho$ and inverse temperature $\beta$ differs from the one of the non-interacting system by the correction term $4 \pi \rho^2 |\ln a^2 \rho|^{-1} (2 - [1 - \beta_{\mathrm{c}}/\beta]_+^2)$. Here $a$ is the scattering length of the interaction potential, $[\cdot]_+ = \max\{ 0, \cdot \}$ and $\beta_{\mathrm{c}}$ is the inverse Berezinskii--Kosterlitz--Thouless critical temperature for superfluidity. The result is valid in the dilute limit $a^2\rho \ll 1$ and if $\beta \rho \gtrsim 1$.
- arXiv:1910.10370 (replaced) [pdf, other]
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Title: Finding the ground states of symmetric infinite-dimensional Hamiltonians: explicit constrained optimizations of tensor networksAuthors: S. N. SaadatmandComments: 8 pages, 1 figure, and no supplemental material. v4: comments are welcomeJournal-ref: J. Phys.: Condens. Matter 32 355901 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el); Computational Physics (physics.comp-ph); Quantum Physics (quant-ph)
Understanding extreme non-locality in many-body quantum systems can help resolve questions in thermostatistics and laser physics. The existence of symmetry selection rules for Hamiltonians with non-decaying terms on infinite-size lattices can lead to finite energies per site, which deserves attention. Here, we present a tensor network approach to construct the ground states of nontrivial symmetric infinite-dimensional spin Hamiltonians based on constrained optimizations of their infinite matrix product states description, which contains no truncation step, offers a very simple mathematical structure, and other minor advantages at the cost of slightly higher polynomial complexity in comparison to an existing method. More precisely speaking, our proposed algorithm is in part equivalent to the more generic and well-established solvers of infinite density-matrix renormalization-group and variational uniform matrix product states, which are, in principle, capable of accurately representing the ground states of such infinite-range-interacting many-body systems. However, we employ some mathematical simplifications that would allow for efficient brute-force optimizations of tensor-network matrices for the specific cases of highly-symmetric infinite-size infinite-range models. As a toy-model example, we showcase the effectiveness and explain some features of our method by finding the ground state of the U(1)-symmetric infinite-dimensional antiferromagnetic $XX$ Heisenberg model.
- arXiv:1910.11718 (replaced) [pdf, other]
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Title: Shelving spectroscopy of the strontium intercombination lineAuthors: I. Manai, A. Molineri, C. Fréjaville, C. Duval, P. Bataille, R. Journet, F. Wiotte, B. Laburthe-Tolra, E. Maréchal, M. Cheneau, M. Robert-de-Saint-VincentJournal-ref: J. Phys. B: At. Mol. Opt. Phys. 53 085005 (2020)Subjects: Atomic Physics (physics.atom-ph); Quantum Gases (cond-mat.quant-gas)
We present a spectroscopy scheme for the 7-kHz-wide 689-nm intercombination line of strontium. We rely on shelving detection, where electrons are first excited to a metastable state by the spectroscopy laser before their state is probed using the broad transition at 461 nm. As in the similar setting of calcium beam clocks, this enhances dramatically the signal strength as compared to direct saturated fluorescence or absorption spectroscopy of the narrow line. We implement shelving spectroscopy both in directed atomic beams and hot vapor cells with isotropic atomic velocities. We measure a fractional frequency instability $\sim 2 \times 10^{-12}$ at 1 s limited by technical noise - about one order of magnitude above shot noise limitations for our experimental parameters. Our work illustrates the robustness and flexibility of a scheme that can be very easily implemented in the reference cells or ovens of most existing strontium experiments, and may find applications for low-complexity clocks.
- arXiv:1910.13748 (replaced) [pdf, ps, other]
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Title: Revisit the non-locality of Majorana zero modes and teleportation: Bogoliubov-de Gennes equation based treatmentComments: 12 pages, 4 figuresJournal-ref: Phys. Rev. B 101, 205401 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Quantum Physics (quant-ph)
The nonlocal nature of the Majorana zero modes implies an inherent teleportation channel and unique transport signatures for Majorana identification. In this work we make an effort to eliminate some inconsistencies between the Bogoliubov-de Gennes equation based treatment and the method using the associated regular fermion number states of vacancy and occupation within the `second quantization' framework. We first consider a rather simple `quantum dot--Majorana wire--quantum dot' system, then a more experimentally relevant setup by replacing the quantum dots with transport leads. For the latter setup, based on the dynamical evolution of electron-hole excitations, we develop a single-particle-wavefunction approach to quantum transport, which renders both the conventional quantum scattering theory and the steady-state nonequilibrium Green's function formalism as its stationary limit. Further, we revisit the issue of Majorana tunneling spectroscopy and consider in particular the two-lead coupling setup. We present comprehensive discussions with detailed comparisons, and predict a zero-bias-limit conductance of $e^2/h$ (for symmetric coupling to the leads),which is a half of the popular result of the zero-bias-peak, or, the so-called Majorana quantized conductance ($2e^2/h$). The present work may arouse a need to reexamine some existing studies and the proposed treatment is expected to be involved in analyzing future experiments in this fast developing field.
- arXiv:1911.00894 (replaced) [pdf]
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Title: Spin and Magnetism in 2D MaterialsAuthors: Roland K. KawakamiComments: 3 pages, 2 figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci)
We review recent progress on spins and magnetism in 2D materials including graphene, transition metal dichalcogenides, and 2D magnets. We also discuss challenges and prospects for the future of spintronics with 2D van der Waals heterostructures.
- arXiv:1911.07131 (replaced) [pdf]
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Title: Mechanical and Vibrational Characteristics of Functionally Graded Cu-Ni Nanowire: A Molecular Dynamics StudyAuthors: Mahmudul Islam, Md Shajedul Hoque Thakur, Satyajit Mojumder, Abdullah Al Amin, Md Mahbubul IslamComments: 45 pages, 11 figuresSubjects: Materials Science (cond-mat.mtrl-sci)
Functionally graded material (FGM) is a class of advanced materials, consisting of two (or more) different constituents, that possesses a continuously varying composition profile. With the advancement of nanotechnology, applications of FGMs have shifted from their conventional usage towards sophisticated micro and nanoscale electronics and energy conversion devices. Therefore, the study of mechanical and vibrational properties of different FGM nanostructures is crucial in exploring their feasibility for different applications. In this study, for the first time, we employed molecular dynamics (MD) simulations to investigate the mechanical and vibrational properties of radially graded Cu-Ni FGM nanowires (NW). Distribution of Cu and Ni along the radial direction follows power-law, exponential and sigmoid functions for FGM NWs under consideration. Our results demonstrate that, distribution function parameters play an important role in modulating the mechanical (elastic modulus and ultimate tensile strength) and vibrational (natural frequency and quality factor) properties of FGM NWs. The study also suggests that, elastic moduli of FGM NWs can be predicted with relatively good accuracy using Tamura and Reuss micromechanical models, regardless of NW diameter. We found that, Euler-Bernoulli beam theory under-predicts the natural frequencies of FGM NWs, whereas He-Lilley model closely approximates the MD results. Interestingly, FGM NWs are always found to exhibit beat vibration because of their asymmetrical cross sections. Finally, this is the first atomistic scale study of FGMs that directly compares MD simulations with continuum theories and micromechanical models to understand the underlying mechanisms that govern the mechanical and vibrational properties of FGM NWs in nanoscale.
- arXiv:1911.07895 (replaced) [pdf, other]
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Title: Deligne Categories in Lattice Models and Quantum Field Theory, or Making Sense of $O(N)$ Symmetry with Non-integer $N$Comments: 59 pages, many figures; v3 typos fixed, version submitted to journalSubjects: High Energy Physics - Theory (hep-th); Statistical Mechanics (cond-mat.stat-mech); Category Theory (math.CT); Representation Theory (math.RT)
When studying quantum field theories and lattice models, it is often useful to analytically continue the number of field or spin components from an integer to a real number. In spite of this, the precise meaning of such analytic continuations has never been fully clarified, and in particular the symmetry of these theories is obscure. We clarify these issues using Deligne categories and their associated Brauer algebras, and show that these provide logically satisfactory answers to these questions. Simple objects of the Deligne category generalize the notion of an irreducible representations, avoiding the need for such mathematically nonsensical notions as vector spaces of non-integer dimension. We develop a systematic theory of categorical symmetries, applying it in both perturbative and non-perturbative contexts. A partial list of our results is: categorical symmetries are preserved under RG flows; continuous categorical symmetries come equipped with conserved currents; CFTs with categorical symmetries are necessarily non-unitary.
- arXiv:1911.08248 (replaced) [pdf, other]
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Title: Growth of different faces in a body centered cubic lattice: a case of the phase-field-crystal modelingComments: Accepted manuscript to Journal of Crystal GrowthJournal-ref: Journal of Crystal Growth 539C (2020) 125608Subjects: Materials Science (cond-mat.mtrl-sci)
Interface energy and kinetic coefficient of crystal growth strongly depend on the face of the crystalline lattice. To investigate the kinetic anisotropy and velocity of different crystallographic faces we use the hyperbolic (modified) phase field crystal model which takes into account atomic density (as a slow thermodynamic variable) and atomic flux (as a fast thermodynamic variable). Such model covers slow and rapid regimes of interfaces propagation at small and large driving forces during solidification. In example of BCC crystal lattice invading the homogeneous liquid, dynamical regimes of advancing front propagating along the selected crystallographic directions are studied. The obtained velocity and the velocity sequences for different faces are compared with known results.
- arXiv:1911.11057 (replaced) [pdf, other]
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Title: Low-Temperature Phase of the Cd$_2$Re$_2$O$_7$ Superconductor: Ab initio Phonon Calculations and Raman ScatteringAuthors: Konrad J. Kapcia, Maureen Reedyk, Mojtaba Hajialamdari, Andrzej Ptok, Przemysław Piekarz, Fereidoon S. Razavi, Andrzej M. Oleś, Reinhard K. KremerComments: 7 pages, 8 figuresSubjects: Superconductivity (cond-mat.supr-con); Materials Science (cond-mat.mtrl-sci)
Using an {\it ab initio} approach, we report a phonon soft mode in the tetragonal structure described by the space group $I4_{1}22$ of the $1$ K $5d$ superconductor Cd$_2$Re$_2$O$_7$. It induces an orthorhombic distortion to a crystal structure described by the space group $F222$ which hosts the superconducting state. This new phase has a lower total energy than the other known crystal structures of Cd$_2$Re$_2$O$_7$. Comprehensive temperature dependent Raman scattering experiments on isotope enriched samples, $^{116}$Cd$_2$Re$_2{^{18}}$O$_7$, not only confirm the already known structural phase transitions but also allow us to identify a new characteristic temperature regime around $\sim 80$ K, below which the Raman spectra undergo remarkable changes with the development of several sharp modes and mode splitting. Together with the results of the \textit{ab initio} phonon calculations we take these observations as strong evidence for another phase transition to a novel low-temperature crystal structure of Cd$_2$Re$_2$O$_7$.
- arXiv:1911.12158 (replaced) [pdf, ps, other]
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Title: Efficiency and irreversibility of movements in a cityComments: 25 pages, 12 figuresJournal-ref: Sci Rep 10, 4334 (2020)Subjects: Physics and Society (physics.soc-ph); Disordered Systems and Neural Networks (cond-mat.dis-nn)
We know that maximal efficiency in physical systems is attained by reversible processes. It is then interesting to see how irreversibility affects efficiency in other systems, e.g., in a city. In this study, we focus on a cyclic process of movements (home to workplace and back to home) in a city to investigate the above question. To this end, we present a minimal model of the movements, along with plausible definitions for the efficiency and irreversibility of the process; more precisely, we take the inverse of the total travel time per number of trips for efficiency and the relative entropy of the forward and backward flow distributions for the process irreversibility. We perform numerical simulations of the model for reasonable choices of the population distribution, the mobility law, and the movement strategy. The results show that the efficiency of movements is indeed negatively correlated with the above measure of irreversibility. The structure of the network and the impact of the flows on the travel times are the main factors here that affect the time intervals of arriving to destinations and returning to origins, which are usually larger than the time interval of the departures. This in turn gives rise to diverging of the backward flows from the forward ones and results to entropy (disorder or uncertainty) production in the system. The findings of this study might be helpful in characterizing more accurately the city efficiency and in better understanding of the main working principles of these complex systems.
- arXiv:1912.08701 (replaced) [pdf, other]
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Title: Multiple perfectly-transmitting states of a single-level at strong couplingComments: Published version plus extra appendices (9 pages with 6 figures)Journal-ref: EPL 129, 47001 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Optics (physics.optics); Quantum Physics (quant-ph)
We study transport through a single-level system placed between two reservoirs with band-structure, taking strong level-reservoir coupling of the order of the energy-scales of these band-structures. An exact solution in the absence of interactions gives the nonlinear Lamb shift. As expected, this moves the perfectly-transmitting state (the reservoir state that flows through the single-level without reflection), and can even turn it into a bound-state. However, here we show that it can also create additional pairs of perfectly-transmitting states at other energies, when the coupling exceeds critical values. Then the single-level's transmission function resembles that of a multi-level system. Even when the discrete level is outside the reservoirs' bands, additional perfectly-transmitting states can appear inside the band when the coupling exceeds a critical value. We propose observing the bosonic version of this in microwave cavities, and the fermionic version in the conductance of a quantum dot coupled to 1D or 2D reservoirs.
- arXiv:1912.10650 (replaced) [pdf, other]
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Title: Weighted Ensemble Milestoning (WEM): A Combined Approach for Rare Event SimulationsSubjects: Statistical Mechanics (cond-mat.stat-mech); Computational Physics (physics.comp-ph)
To directly simulate rare events using atomistic molecular dynamics is a significant challenge in computational biophysics. Well-established enhanced-sampling techniques do exist to obtain the thermodynamic functions for such systems. But developing methods for obtaining the kinetics of long timescale processes from simulation at atomic detail is comparatively less developed an area. Milestoning and the weighted ensemble (WE) method are two different stratification strategies; both have shown promise for computing long timescales of complex biomolecular processes. Nevertheless, both require a significant investment of computational resources. We have combined WE and milestoning to calculate observables in orders of magnitude less CPU and wall-clock time. Our weighted ensemble milestoning method (WEM) uses WE simulation to converge the transition probability and first passage times between milestones, followed by the utilization of the theoretical framework of milestoning to extract thermodynamic and kinetic properties of the entire process. We tested our method for a simple one-dimensional double well potential, an eleven-dimensional potential energy surface with energy barrier, and on the biomolecular model system alanine dipeptide. We were able to recover the free energy profiles, time correlation functions, and mean first passage times for barrier crossing events at a significantly small computational cost. WEM promises to extend the applicability of molecular dynamics simulation to slow dynamics of large systems which are well beyond the scope of present day brute-force computations.
- arXiv:2001.00511 (replaced) [pdf, ps, other]
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Title: Longitudinal magnetization dynamics in the quantum Ising ring: A Pfaffian method based on correspondence between momentum space and real spaceAuthors: Ning WuComments: 14 pages, 4 figures, to appear in Physical Review EJournal-ref: Phys. Rev. E 101, 042108 (2020)Subjects: Quantum Physics (quant-ph); Strongly Correlated Electrons (cond-mat.str-el)
As perhaps the most studied paradigm for a quantum phase transition, the periodic quantum Ising chain is exactly solvable via the Jordan-Wigner transformation followed by a Fourier transform that diagonalizes the model in the momentum space of spinless fermions. Although the above procedures are well-known, there remain some subtle points to be clarified regarding the correspondence between the real-space and momentum-space representations of the quantum Ising ring, especially those related to fermion parities. In this work, we establish the relationship between the two fully aligned ferromagnetic states in real space and the two degenerate momentum-space ground states of the classical Ising ring, with the former being a special case of the factorized ground states of the more general XYZ model on the frustration-free hypersurface. Based on this observation, we then provide a Pfaffian formula for calculating real-time dynamics of the parity-breaking longitudinal magnetization with the system initially prepared in one of the two ferromagnetic states and under translationally invariant drivings. The formalism is shown to be applicable to systems with the help of online programs for the numerical computation of the Pfaffian, thus providing an efficient method to numerically study, for example, the emergence of discrete time crystals in related systems.
- arXiv:2001.03462 (replaced) [pdf, other]
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Title: Long-Range Phonon Spin Transport in Ferromagnet-Nonmagnetic Insulator HeterostructuresComments: 6 pages, 4 figuresJournal-ref: Phys. Rev. Lett. 124, 117201 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We investigate phonon spin transport in an insulating ferromagnet-nonmagnet-ferromagnet heterostructure. We show that the magnetoelastic interaction between the spins and the phonons leads to nonlocal spin transfer between the magnets. This transfer is mediated by a local phonon spin current and accompanied by a phonon spin accumulation. The spin conductance depends nontrivially on the system size, and decays over millimeter length scales for realistic material parameters, far exceeding the decay lengths of magnonic spin currents.
- arXiv:2001.06279 (replaced) [pdf, ps, other]
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Title: Methods of electron transport in ab initio theory of spin stiffnessComments: 10 pages, 4 figures, 2 tables; text slightly extended; accepted in Phys. Rev. BJournal-ref: Phys. Rev. B 101, 134410 (2020)Subjects: Materials Science (cond-mat.mtrl-sci)
We present an ab initio theory of the spin-wave stiffness tensor for ordered and disordered itinerant ferromagnets with pair exchange interactions derived from a method of infinitesimal spin rotations. The resulting formula bears an explicit form of a linear-response coefficient which involves one-particle Green's functions and effective velocity operators encountered in a recent theory of electron transport. Application of this approach to ideal metal crystals yields more reliable values of the spin stiffness than traditional ill-convergent real-space lattice summations. The formalism can also be combined with the coherent potential approximation for an effective-medium treatment of random alloys, which leads naturally to an inclusion of disorder-induced vertex corrections to the spin stiffness. The calculated concentration dependence of the spin-wave stiffness of random fcc Ni-Fe alloys can be ascribed to a variation of the reciprocal value of alloy magnetization. Calculations for random iron-rich bcc Fe-Al alloys reveal that their spin-wave stiffness is strongly reduced owing to the atomic ordering; this effect takes place due to weakly coupled local magnetic moments of Fe atoms surrounded by a reduced number of Fe nearest neighbors.
- arXiv:2003.00994 (replaced) [pdf, other]
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Title: Machine learning spectral indicators of topologyComments: 14 pages, 3 main figures and 5 supplementary figures. Feedback most welcomeSubjects: Disordered Systems and Neural Networks (cond-mat.dis-nn); Materials Science (cond-mat.mtrl-sci); Computational Physics (physics.comp-ph)
Topological materials discovery has emerged as an important frontier in condensed matter physics. Recent theoretical approaches based on symmetry indicators and topological quantum chemistry have been used to identify thousands of candidate topological materials, yet experimental determination of materials' topology often poses significant technical challenges. X-ray absorption spectroscopy (XAS) is a widely-used materials characterization technique sensitive to atoms' local symmetry and chemical environment; thus, it may encode signatures of materials' topology, though indirectly. In this work, we show that XAS can potentially uncover materials' topology when augmented by machine learning. By labelling computed X-ray absorption near-edge structure (XANES) spectra of over 16,000 inorganic materials with their topological class, we establish a machine learning-based classifier of topology with XANES spectral inputs. Our classifier correctly predicts 81% of topological and 80% of trivial cases, and can achieve 90% and higher accuracy for materials containing certain elements. Given the simplicity of the XAS setup and its compatibility with multimodal sample environments, the proposed machine learning-empowered XAS topological indicator has the potential to discover broader categories of topological materials, such as non-cleavable compounds and amorphous materials. It can also inform a variety of field-driven phenomena in situ, such as magnetic field-driven topological phase transitions.
- arXiv:2003.01748 (replaced) [pdf, other]
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Title: Phononless high-performance thermoelectricity in quantum-Hall Corbino structuresAuthors: Mariano Real, Daniel Gresta, Christian Reichl, Jurgen Weis, Alejandra Tonina, Paula Giudici, Liliana Arrachea, Werner Wegscheider, Werner DietscheComments: main article 6 pages, 5 figures, supplementary material 6 pages, and 6 figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Quantum Physics (quant-ph)
We measure the thermoelectric response of Corbino structures in the quantum Hall effect regime and compared it with a theoretical analysis. The measured thermoelectric voltages are qualitatively and quantitatively simulated based upon the independent measurement of the conductivity indicating that they originate predominantly from the electron diffusion. Electron-phonon interaction does not lead to a phonon-drag contribution in contrast to earlier Hall-bar experiments. This implies a description of the Onsager coefficients on the basis of a single transmission function, from which a figure of merit can be estimated which becomes very large for partially filled Landau levels and high magnetic fields.
- arXiv:2003.02722 (replaced) [pdf, other]
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Title: Chemical Bonding in Metallic Glasses from Machine Learning and Crystal Orbital Hamilton PopulationAuthors: Ary R. FerreiraComments: The manuscript has been restructured so that it can be published as an article. Although some few arguments have been revised, results are the sameSubjects: Materials Science (cond-mat.mtrl-sci); Chemical Physics (physics.chem-ph); Computational Physics (physics.comp-ph)
The chemistry (composition and bonding information) of metallic glasses (MGs) is at least as important as structural topology for understanding their properties and production/processing peculiarities. This article reports a machine learning (ML)-based approach that brings an unprecedented "big picture" view of chemical bond strengths in MGs of a prototypical alloy system. The connection between electronic structure and chemical bonding is given by crystal orbital Hamilton population (COHP) analysis within the framework of density functional theory (DFT). The stated comprehensive overview is made possible through a combination of efficient quantitative estimate of bond strengths supplied by COHP analysis, representative statistics regarding structure in terms of atomic configurations achieved with classical molecular dynamics simulations, and the smooth overlap of atomic positions (SOAP) descriptor. The study is supplemented by an application of that ML model under the scope of mechanical loading, in which predicted bond strengths enabled atom categorization based on a descriptor of the short-range order possessing a superior chemical sense; a key component to uncover structural/chemical heterogeneity and its influence on mechanical relaxation processes and atomic scale flow mechanisms in MGs.
- arXiv:2003.03126 (replaced) [pdf, ps, other]
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Title: Metastability in the Potts model: exact results in the large q limitComments: 29 pages, 8 figuresSubjects: Statistical Mechanics (cond-mat.stat-mech)
We study the metastable equilibrium properties of the Potts model with heat-bath transition rates using a novel expansion. The method is especially powerful for large number of state spin variables and it is notably accurate in a rather wide range of temperatures around the phase transition.
- arXiv:2003.05424 (replaced) [pdf, other]
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Title: Dual Majorana universality in thermally induced nonequilibriumAuthors: Sergey SmirnovComments: 7 pages, 7 figuresJournal-ref: Physical Review B 101, 125417 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Superconductivity (cond-mat.supr-con)
We demonstrate that nonequilibrium nanoscopic systems with Majorana zero modes admit special kind of universality which cannot be classified as of strictly transport or strictly thermodynamic nature. To reveal such kind of Majorana universality we explore purely thermal nonequilibrium states of a quantum dot whose low-energy degrees of freedom are governed by Majorana zero modes. Specifically, the quantum dot is coupled to a topological superconductor, supporting Majorana zero modes, as well as to two normal metallic contacts with the same chemical potentials but different temperatures. It is shown that the Majorana universality in this setup is dual: it is stored inside both the response of the electric current, excited by exclusively the temperature difference, and the quantum dot compressibility. The latter is defined as the derivative of the quantum dot particle number with respect to the chemical potential and forms a universal Majorana ratio with a proper derivative of the electric current that flows in nonequilibrium states of purely thermal nature.
- arXiv:2003.05566 (replaced) [pdf, ps, other]
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Title: Ion Modes in Dense Ionized Plasmas through Non-Adiabatic Molecular DynamicsComments: 5 pages and 4 figures in the main manuscript, 6 pages and 9 figures in the supplementary information; typos corrected; corrected grammar, references fixed, author name adjustedSubjects: Plasma Physics (physics.plasm-ph); Statistical Mechanics (cond-mat.stat-mech); Computational Physics (physics.comp-ph)
We perform non-adiabatic simulations of warm dense aluminum based on the electron-force field (EFF) variant of wave-packet molecular dynamics. Comparison of the static ion-ion structure factor with density functional theory is used to validate the technique across a range of temperatures and densities spanning the warm dense matter regime. Differences in the dynamic structure factor and dispersion relation between adiabatic and non-adiabatic techniques suggest that the explicit inclusion of electrons is necessary to fully capture the low frequency dynamics of the response function.
- arXiv:2003.05966 (replaced) [pdf, other]
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Title: Hypersensitive tunable Josephson escape sensor for gigahertz astronomyAuthors: Federico Paolucci, Nadia Ligato, Vittorio Buccheri, Gaia Germanese, Pauli Virtanen, Francesco GiazottoComments: 13 pages, 8 figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Superconductivity (cond-mat.supr-con)
Sensitive photon detection in the gigahertz band constitutes the cornerstone to study different phenomena in astronomy, such as radio burst sources, galaxy formation, cosmic microwave background, axions, comets, gigahertz-peaked spectrum radio sources and supermassive black holes. Nowadays, state of the art detectors for astrophysics are mainly based on transition edge sensors and kinetic inductance detectors. Overall, most sensible nanobolometers so far are superconducting detectors showing a noise equivalent power (NEP) as low as 2x10-20 W/Hz1/2. Yet, fast thermometry at the nanoscale was demonstrated as well with Josephson junctions through switching current measurements. In general, detection performance are set by the fabrication process and limited by used materials. Here, we conceive and demonstrate an innovative tunable Josephson escape sensor (JES) based on the precise current control of the temperature dependence of a fully superconducting one-dimensional nanowire Josephson junction. The JES might be at the core of future hypersensitive in situ-tunable bolometers or single-photon detectors working in the gigahertz regime. Operated as a bolometer the JES points to a thermal fluctuation noise (TFN) NEP_TFN 1x10-25 W/Hz1/2, which as a calorimeter bounds the frequency resolution above 2 GHz, and resolving power below 40 at 50 GHz, as deduced from the experimental data. Beyond the obvious applications in advanced ground-based and space telescopes for gigahertz astronomy, the JES might represent a breakthrough in several fields of quantum technologies ranging from subTHz communications and quantum computing to cryptography and quantum key distribution.
- arXiv:2003.06558 (replaced) [pdf, ps, other]
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Title: Electro-osmotic properties of porous permeable filmsSubjects: Soft Condensed Matter (cond-mat.soft); Chemical Physics (physics.chem-ph)
Permeable porous coatings on a flat solid support significantly impact its electrostatic and electrokinetic properties. Existing work has focused on simplified cases, such as weakly charged and/or thick porous films, with limited theoretical guidance. Here, we consider the general case of coatings of any given volume charge density and obtain analytic formulas for electrostatic potential profiles, valid for any film thickness and salt concentration. They allow us to calculate analytically the difference between potentials at solid support and at interface with an outer electrolyte, that is the key parameter ascertaining the functionality of permeable coatings. Our analysis provides a framework for interpreting and predicting specific for porous films super-properties, from an enhanced ion absorption to a giant amplification of electro-osmotic flows. The results are relevant for hydrogel and zeolite coatings, porous carbon and ion-exchange resins, polyelectrolyte brushes, and more.
- arXiv:2003.06601 (replaced) [pdf, other]
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Title: Lattice protein design using Bayesian learningComments: 9 pages, 8 figuresSubjects: Biological Physics (physics.bio-ph); Statistical Mechanics (cond-mat.stat-mech); Machine Learning (cs.LG); Chemical Physics (physics.chem-ph)
A novel protein design method using Bayesian learning is proposed in this work. We consider a posterior probability of amino acid sequences by taking into account water and assuming a prior of sequences. For some instances of a target conformation of a two-dimensional (2D) lattice Hydrophobic-Polar (HP) model, our method successfully finds an amino acid sequence for which the target conformation has a unique ground state. However, the performance was not as good for 3D lattice HP models compared with 2D models. Furthermore, we find a strong linearity between the chemical potential of water and the number of surface residues, thereby revealing the relationship between protein structure and the effect of water molecules. The advantage of our method is that it greatly reduces computation time, because it does not require long calculations for the partition function corresponding to an exhaustive conformational search. As our method uses a general form of Bayesian learning and statistical mechanics and is not limited to lattice HP proteins, the results presented here elucidate some heuristics used successfully in previous protein design methods.
- arXiv:2003.07079 (replaced) [pdf]
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Title: Spin orbit field in a physically defined p type MOS silicon double quantum dotAuthors: Marian Marx, Jun Yoneda, Ángel Gutiérrez Rubio, Peter Stano, Tomohiro Otsuka, Kenta Takeda, Sen Li, Yu Yamaoka, Takashi Nakajima, Akito Noiri, Daniel Loss, Tetsuo Kodera, Seigo TaruchaComments: 21 pages, 4 figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Applied Physics (physics.app-ph); Quantum Physics (quant-ph)
We experimentally and theoretically investigate the spin orbit (SO) field in a physically defined, p type metal oxide semiconductor double quantum dot in silicon. We measure the magnetic field dependence of the leakage current through the double dot in the Pauli spin blockade. A finite magnetic field lifts the blockade, with the lifting least effective when the external and SO fields are parallel. In this way, we find that the spin flip of a tunneling hole is due to a SO field pointing perpendicular to the double dot axis and almost fully out of the quantum well plane. We augment the measurements by a derivation of SO terms using group symmetric representations theory. It predicts that without in plane electric fields (a quantum well case), the SO field would be mostly within the plane, dominated by a sum of a Rashba and a Dresselhaus like term. We, therefore, interpret the observed SO field as originated in the electric fields with substantial in plane components.
- arXiv:2003.07643 (replaced) [pdf, other]
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Title: Solution landscape of a reduced Landau-de Gennes model on a hexagonComments: 15 pages, 10 figuresSubjects: Mathematical Physics (math-ph); Soft Condensed Matter (cond-mat.soft)
We investigate the solution landscape of a reduced Landau--de Gennes model for nematic liquid crystals on a two-dimensional hexagon at a fixed temperature, as a function of $\lambda$---the edge length. This is a generic example for reduced approaches on regular polygons. We apply the high-index optimization-based shrinking dimer method to systematically construct the solution landscape consisting of multiple defect solutions and relationships between them. We report a new stable T state with index-$0$ that has an interior $-1/2$ defect; new classes of high-index saddle points with multiple interior defects referred to as H class and TD class; changes in the Morse index of saddle points with $\lambda^2$ and novel pathways mediated by high-index saddle points that can control and steer dynamical pathways. The range of topological degrees, locations and multiplicity of defects offered by these saddle points can be used to navigate through complex solution landscapes of nematic liquid crystals and other related soft matter systems.
- arXiv:1408.3663 (replaced) [pdf, ps, other]
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Title: Emergence of a non-Fowler-Nordheim-type behavior for a general planar tunneling barrierComments: 5 pages. Improved version. Title modified. Abstract rewritten. References updatedJournal-ref: Physics Letters A (2020)Subjects: Materials Science (cond-mat.mtrl-sci)
In this work we investigate a generalized tunneling barrier for planar emitters at zero-temperature. We present the evidence of the emergence of a non-Fowler-Nordheim-type general behavior for the field emission current density in the case that the Fermi energy ($\mu$) is comparable with or smaller that the decay width ($d_F$). Therefore, for some non-metals or materials that have very small Fermi energy the standard Fowler-Nordheim-type theory may require a correction. In the opposite regime, i.e., for $\mu$ much larger that $d_F$, we confirm that the conventional theory is suitable for metals.
- arXiv:1511.02776 (replaced) [pdf, ps, other]
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Title: Explicit formulas for reaction probability in reaction-diffusion experimentsJournal-ref: Comput. Chem. Eng., 125 (2019), 612-622Subjects: Soft Condensed Matter (cond-mat.soft); Mathematical Physics (math-ph); Numerical Analysis (math.NA)
A computational procedure is developed for determining the conversion probability for reaction-diffusion systems in which a first-order catalytic reaction is performed over active particles. We apply this general method to systems on metric graphs, which may be viewed as 1-dimensional approximations of 3-dimensional systems, and obtain explicit formulas for conversion. We then study numerically a class of 3-dimensional systems and test how accurately they are described by model formulas obtained for metric graphs. The optimal arrangement of active particles in a 1-dimensional multiparticle system is found, which is shown to depend on the level of catalytic activity: conversion is maximized for low catalytic activity when all particles are bunched together close to the point of gas injection, and for high catalytic activity when the particles are evenly spaced.
- arXiv:1806.08614 (replaced) [pdf, other]
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Title: Tuneable topological domain wall states in engineered atomic chainsJournal-ref: npj Quantum Materials 5, 17 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Topological modes in one- and two-dimensional systems have been proposed for numerous applications utilizing their exotic electronic responses. The zero-energy, topologically protected end modes can be realized in the Su-Schrieffer-Heeger (SSH) model, which has been experimentally implemented in atomic-scale solid-state structures and in ultra-cold atomic gases. While the edge modes in the SSH model are at exactly the mid-gap energy, other paradigmatic 1D models such as trimer and coupled dimer chains have non-zero energy boundary states. However, these chains have not been realized in an atomically tuneable system that would allow explicit control of the edge modes. Here, we demonstrate atomically controlled trimer and coupled dimer chains realized using chlorine vacancies in the c$(2\times2)$ adsorption layer on Cu(100). This system allows wide tuneability of the domain wall modes that we experimentally demonstrate using low-temperature scanning tunneling microscopy (STM). In the future, these modes may be used to realize well-defined fractional charge states or find applications in exotic quantum devices with atomically well-defined geometries.
- arXiv:1807.05998 (replaced) [pdf, other]
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Title: A Solution to the 1+1D Gauged Chiral Fermion ProblemComments: v3: Refinement. The complete mathematical proof is given in arXiv:1307.7480Journal-ref: Phys. Rev. D 99, 111501(R) (2019)Subjects: High Energy Physics - Lattice (hep-lat); Strongly Correlated Electrons (cond-mat.str-el); High Energy Physics - Phenomenology (hep-ph); High Energy Physics - Theory (hep-th)
We show that the 3450 U(1) chiral fermion theory can appear as the low energy effective field theory of a 1+1D local lattice model, with an on-site U(1) symmetry and finite-range interactions. The on-site U(1) symmetry means that the U(1) symmetry can be gauged (gaugeable for both background probe and dynamical fields), which leads to a non-perturbative definition of chiral gauge theory --- a chiral fermion theory coupled to U(1) gauge theory. Our construction can be generalized to regularize any U(1)-anomaly-free 1+1D gauged chiral fermion theory with a zero chiral central charge (thus no gravitational anomaly) by a lattice, thanks to the recently proven "Poincar\'e dual" equivalence between the U(1) 't Hooft anomaly free condition and the U(1) symmetric interaction gapping rule, via a bosonization-fermionization technique.
- arXiv:1810.12869 (replaced) [pdf, ps, other]
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Title: Quantum measurements of timeComments: 4 pages+appendices (=supplemental material). Version accepted for publication on Phys. Rev. LettJournal-ref: Phys. Rev. Lett. 124, 110402 (2020)Subjects: Quantum Physics (quant-ph); Quantum Gases (cond-mat.quant-gas); Statistical Mechanics (cond-mat.stat-mech)
We propose a time-of-arrival operator in quantum mechanics by conditioning on a quantum clock. This allows us to bypass some of the problems of previous proposals, and to obtain a Hermitian time of arrival operator whose probability distribution arises from the Born rule and which has a clear physical interpretation. The same procedure can be employed to measure the "time at which some event happens" for arbitrary events (and not just specifically for the arrival time of a particle).
- arXiv:1901.03449 (replaced) [pdf, other]
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Title: Efficient Ab Initio Calculations of Electron-Defect Scattering and Defect-Limited Carrier MobilityComments: 11 pages, 5 figures, submittedJournal-ref: Phys. Rev. Materials 3, 033804 (2019)Subjects: Materials Science (cond-mat.mtrl-sci)
Electron-defect ($e$-d) interactions govern charge carrier dynamics at low temperature, where they limit the carrier mobility and give rise to phenomena of broad relevance in condensed matter physics. Ab initio calculations of $e$-d interactions are still in their infancy, mainly because they require large supercells and computationally expensive workflows. Here we develop an efficient ab initio approach for computing elastic $e$-d interactions, their associated $e$-d relaxation times (RTs), and the low-temperature defect-limited carrier mobility. The method is applied to silicon with simple neutral defects, such as vacancies and interstitials. Contrary to conventional wisdom, the computed $e$-d RTs depend strongly on carrier energy and defect type, and the defect-limited mobility is temperature dependent. These results highlight the shortcomings of widely employed heuristic models of $e$-d interactions in materials. Our method opens new avenues for studying $e$-d scattering and low-temperature charge transport from first principles.
- arXiv:1903.03038 (replaced) [pdf]
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Title: Aperiodic quantum oscillations in the two-dimensional electron gas at the LaAlO3/SrTiO3 interfaceAuthors: Km Rubi, Julien Gosteau, Raphaël Serra, Kun Han, Shengwei Zeng, Zhen Huang, Etienne Snoeck, Rémi Arras, Benedicte Warot-Fonrose, Ariando, Michel Goiran, Walter EscoffierSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Despite several attempts, the intimate electronic structure of two-dimensional electron systems buried at the interface between LaAlO3 and SrTiO3 still remains to be experimentally revealed. Here, we investigate the transport properties of a high-mobility quasi-two-dimensional electron gas at this interface under high magnetic field (55 T) and provide new insights for electronic band structure by analyzing the Shubnikov-de Haas oscillations. Interestingly, the quantum oscillations are not 1/B-periodic and produce a highly non-linear Landau plot (Landau level index versus 1/B). Among possible scenarios, the Roth-Gao-Niu equation provides a natural explanation for 1/B-aperiodic oscillations in relation with the magnetic response functions of the system. Overall, the magneto-transport data are discussed in light of high-resolution scanning transmission electron microscopy analysis of the interface as well as calculations from density functional theory.
- arXiv:1903.09652 (replaced) [pdf, other]
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Title: Quench, thermalization and residual entropy across a non-Fermi liquid to Fermi liquid transitionComments: 5 pages, 3 figures, and supplementary materialJournal-ref: Phys. Rev. Research 2, 013307 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el); High Energy Physics - Theory (hep-th)
We study the thermalization, after sudden and slow quenches, of an interacting model having a quantum phase transition from a Sachdev-Ye-Kitaev (SYK) non-Fermi liquid (NFL) to a Fermi liquid (FL). The model has SYK fermions coupled to non-interacting lead fermions and can be realized in a graphene flake connected to external leads. After a sudden quench to the NFL, a thermal state is reached rapidly via collapse-revival oscillations of the quasiparticle residue of the lead fermions. In contrast, the quench to the FL, across the NFL-FL transition, leads to multiple prethermal regimes and much slower thermalization. In the slow quench performed over a time $\tau$, we find that the excitation energy generated has a remarkable intermediate-$\tau$ non-analytic power-law dependence, $\tau^{-\eta}$ with $\eta<1$, which seemingly masks the dynamical manifestation of the initial residual entropy of the SYK fermions. The power-law scaling is expected to eventually break down for $\tau\to\infty$, signaling a violation of adiabaticity, due to the residual entropy present in the SYK fermions.
- arXiv:1906.09401 (replaced) [pdf, other]
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Title: Higgs Mode in SuperconductorsComments: 33 pages, 10 figures; a review article submitted to Annual Review of Condensed Matter PhysicsJournal-ref: Annu. Rev. Condens. Matter Phys. 11, 103 (2020)Subjects: Superconductivity (cond-mat.supr-con); Strongly Correlated Electrons (cond-mat.str-el)
When a continuous symmetry of a physical system is spontaneously broken, two types of collective modes typically emerge: the amplitude and phase modes of the order-parameter fluctuation. For superconductors, the amplitude mode is recently referred to as the ''Higgs mode'' as it is a condensed-matter analogue of a Higgs boson in particle physics. Higgs mode is a scalar excitation of the order parameter, distinct from charge or spin fluctuations, and thus does not couple to electromagnetic fields linearly. This is why the Higgs mode in superconductors has evaded experimental observations over a half century after the initial theoretical prediction, except for a charge-density-wave coexisting system. With the advance of nonlinear and time-resolved terahertz spectroscopy techniques, however, it has become possible to study the Higgs mode through the nonlinear light-Higgs coupling. In this review, we overview recent progresses on the study of the Higgs mode in superconductors.
- arXiv:1907.01016 (replaced) [pdf, other]
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Title: Topological edge states of interacting photon pairs emulated in a topolectrical circuitAuthors: Nikita A. Olekhno, Egor I. Kretov, Andrei A. Stepanenko, Polina A. Ivanova, Vitaly V. Yaroshenko, Ekaterina M. Puhtina, Dmitry S. Filonov, Barbara Cappello, Ladislau Matekovits, Maxim A. GorlachComments: 7 pages, 3 figures+Supplementary Materials. Added references and extended discussionJournal-ref: Nature Communications 11, 1436 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Optics (physics.optics); Quantum Physics (quant-ph)
Topological physics opens up a plethora of exciting phenomena allowing to engineer disorder-robust unidirectional flows of light. Recent advances in topological protection of electromagnetic waves suggest that even richer functionalities can be achieved by realizing topological states of quantum light. This area, however, remains largely uncharted due to the number of experimental challenges. Here, we take an alternative route and design a classical structure based on topolectrical circuits which serves as a simulator of a quantum-optical one-dimensional system featuring the topological state of two photons induced by the effective photon-photon interaction. Employing the correspondence between the eigenstates of the original problem and circuit modes, we use the designed simulator to extract the frequencies of bulk and edge two-photon bound states and evaluate the topological invariant directly from the measurements. Furthermore, we perform a reconstruction of the two-photon probability distribution for the topological state associated with one of the circuit eigenmodes.
- arXiv:1907.07997 (replaced) [pdf, ps, other]
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Title: Electric bias-controlled switching of magnetization of ferrimagnetically coupled Mn delta-layers in a GaAs-AlGaAs quantum wellComments: 16 pages, 1 figure, submitted to JMMMSubjects: Strongly Correlated Electrons (cond-mat.str-el)
We suggest a model of synthetic ferrimagnetic semiconductor structure based on GaAs-AlGaAs quantum well doped by two Mn delta-layers. The coupling between the delta-layers is mediated by extra holes, and can be switched between ferro- and antiferromagnetic one by gating the structure. A proper choice of Mn concentrations in the delta-layers and of local degree of disorder enables fabrication of a ferrimagnetic structure supporting ultrafast switching of magnetization by short pulses of electric bias without an external magnetic field. The switching mechanism in the structure relies on kinetic spin exchange between the two delta-layers which is mediated by exchange scattering of electric-pulse heated holes by magnetic ions within the layers. Owing to specific interplay between characteristics of the exchange scattering, spin decay times, and the heat withdraw in the suggested synthetic ferrimagnetic semiconductor, the necessary parameters of electric-bias pulse are within the technologically accessible range, and do not contradict typical thermal kinetics of semiconductor structures.
- arXiv:1907.12423 (replaced) [pdf]
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Title: Muon spin rotation and neutron scattering investigations of the B-site ordered double perovskite Sr2DyRuO6Authors: D.T. Adroja, Shivani Sharma, C. Ritter, A.D. Hillier, C.V. Tomy, R. Singh, R. I. Smith, M. Koza, A. Sundaresan, S. LangridgeComments: 25 pages, 14 figuresJournal-ref: Physical Review B 101, 094413 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el)
The magnetic ground state of double perovskite Sr2DyRuO6 has been investigated using muon spin rotation and relaxation (muSR), neutron powder diffraction (NPD) and inelastic neutron scattering (INS), in addition to heat capacity and magnetic susceptibility (ac and dc) measurements. A clear signature of a long-range ordered magnetic ground state has been observed in the heat capacity data, which exhibit two sharp anomalies at 39.5 and 36 K found as well in the magnetic data. Further confirmation of long-range magnetic ordering comes from a sharp drop in the muon initial asymmetry and a peak in the relaxation rate at 40 K, along with a weak anomaly near 36 K. Based on temperature dependent NPD, the low temperature magnetic structure contains two interpenetrating lattices of Dy and Ru5, forming an antiferromagnetic ground state below 39.5 K with magnetic propagation vector k = (0,0,0). The magnetic moments of Dy and Ru at 3.5 K are pointing along the crystallographic b-axis with values of muDy = 4.92(10) muB and muRu = 1.94(7) muB, respectively. The temperature dependence of the Ru moments follows a mean field type behaviour, while that of the Dy moments exhibits a deviation indicating that the primary magnetic ordering is induced by the order of the 4d electrons of Ru rather than that of its proper 4f Dy electrons. The origin of the second anomaly observed in the heat capacity data at 36.5 K must be connected to a very small spin reorientation as the NPD studies do not reveal any clear change in the observed magnetic Bragg peaks positions or intensities between these two transitions. INS measurements reveal the presence of crystal field excitations (CEF) in the paramagnetic state with overall CEF splitting of 73.8 meV, in agreement with the point change model calculations.
- arXiv:1907.12566 (replaced) [pdf, other]
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Title: Observation of non-Hermitian bulk-boundary correspondence in quantum dynamicsComments: 15 pages, 9 figuresJournal-ref: Nat. Phys. (2020). https://doi.org/10.1038/s41567-020-0836-6Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Quantum Gases (cond-mat.quant-gas); Strongly Correlated Electrons (cond-mat.str-el); Optics (physics.optics); Quantum Physics (quant-ph)
Bulk-boundary correspondence, a central principle in topological matter relating bulk topological invariants to edge states, breaks down in a generic class of non-Hermitian systems that have so far eluded experimental effort. Here we theoretically predict and experimentally observe non-Hermitian bulk-boundary correspondence, a fundamental generalization of the conventional bulk-boundary correspondence, in discrete-time non-unitary quantum-walk dynamics of single photons. We experimentally demonstrate photon localizations near boundaries even in the absence of topological edge states, thus confirming the non-Hermitian skin effect. Facilitated by our experimental scheme of edge-state reconstruction, we directly measure topological edge states, which match excellently with non-Bloch topological invariants calculated from localized bulk-state wave functions. Our work unequivocally establishes the non-Hermitian bulk-boundary correspondence as a general principle underlying non-Hermitian topological systems, and paves the way for a complete understanding of topological matter in open systems.
- arXiv:1909.06330 (replaced) [pdf]
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Title: Minimal Coarse-Grained Modelling Towards Implicit-Solvent Simulation of Generic BolaamphiphilesComments: 9 pages, 9 figuresJournal-ref: J. Phys. Chem. B 2020Subjects: Soft Condensed Matter (cond-mat.soft); Computational Physics (physics.comp-ph)
A simple, dual-site model of bolaamphiphiles (bolaforms or bipolar amphiphiles) is developed based on an earlier single-site model of (monopolar) amphiphiles [S. Dey, J. Saha, Phys. Rev. E 95, 023315 (2017)]. The model incorporates aqueous environment (both hydrophobic effect and hydration force) in its anisotropic site-site interactions, thus obviating the need to simulate solvent particles explicitly. This economy of sites and the absence of explicit solvent particles enable molecular dynamics simulations of bolaamphiphiles to achieve mesoscopic length and time-scales unattainable by any bead-spring model or explicit solvent computations. The model applies to generic bolas only, since the gain in scale can only be obtained by sacrificing the resolution of detailed molecular structure. Thanks to dual-sites, however, (as opposed to a single-site model) our model can incorporate the essential flexibility of bolas that leads to their U-conformers. The model bolas show successful self-assembly into experimentally observed nano-structures like micelles, rods, lamellae etc. and retain fluidity in very stable monolayers. Presence of membrane-spanning model bolas in bilayers of model monopolar amphiphiles increases the stability and impermeability of the lamellar phase. Model bolas are also seen to be less diffusive and to produce thicker layers compared to their monopolar counterparts. Rigid model bolas, though achiral themselves, show self-assembly into helical rods. As all these observations agree with the well-known key characteristics of archaeal lipids and synthetic bolaamphiphiles, our model promises to be effective for studies of bolas in context of biomimetics, drug-delivery and low molecular weight hydrogelators. To the best of our knowledge, no other single or dual-site, solvent-free model for bolas has been reported thus far.
- arXiv:1909.11257 (replaced) [pdf, other]
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Title: A digital PID controller for stabilizing large electric currents to the ppm level for Feshbach resonance studiesComments: To appear in Review of Scientific InstrumentsJournal-ref: Rev. Sci. Instrum. 91, 034705 (2020)Subjects: Atomic Physics (physics.atom-ph); Quantum Gases (cond-mat.quant-gas); Instrumentation and Detectors (physics.ins-det)
Magnetic Feshbach resonances are a key tool in the field of ultracold quantum gases, but their full exploitation requires the generation of large, stable magnetic fields up to 1000 G with fractional stabilities of better than $10^{-4}$. Design considerations for electromagnets producing these fields, such as optical access and fast dynamical response, mean that electric currents in excess of 100 A are often needed to obtain the requisite field strengths. We describe a simple digital proportional-integral-derivative current controller constructed using a field-programmable gate array and off-the-shelf evaluation boards which allows for gain scheduling, enabling optimal control of current sources with non-linear actuators. Our controller can stabilize an electric current of 337.5 A to the level of $7.5\times 10^{-7}$ in an averaging time of 10 minutes and with a control bandwidth of 2 kHz.
- arXiv:1910.08305 (replaced) [pdf]
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Title: A substantial increase of Curie temperature in a new type of diluted magnetic semiconductors via effects of chemical pressureAuthors: Shuang Yu, Guoqiang Zhao, Yi Peng, Xiaohong Zhu, Xiancheng Wang, Jianfa Zhao, Lipeng Cao, Wenmin Li, Zhi Li, Zheng Deng, Changqing JinComments: 19 pages, 4 figuresJournal-ref: APL Mater. 7, 101119 (2019)Subjects: Materials Science (cond-mat.mtrl-sci); Strongly Correlated Electrons (cond-mat.str-el)
Chemical pressure is an effective method to tune physical properties, particularly for diluted magnetic semiconductors (DMS) of which ferromagnetic ordering is mediated by charge carriers. Via substitution of smaller Ca for larger Sr, we introduce chemical pressure on (Sr,Na)(Cd,Mn)2As2 to fabricate a new DMS material (Ca,Na)(Cd,Mn)2As2. Carriers and spins are introduced by substitutions of (Ca,Na) and (Cd,Mn) respectively. The unit cell volume reduces by 6.2% after complete substitution of Ca for Sr, suggesting a subsistent chemical pressure. Importantly the local geometry of [Cd/MnAs4] tetrahedron is optimized via chemical compression that increases the Mn-As hybridization leading to enhanced ferromagnetic interactions. As a result, the maximum Curie temperature (TC) is increased by about 50% while the the maximum saturation moment increases by over 100% from (Sr,Na)(Cd,Mn)2As2 to (Ca,Na)(Cd,Mn)2As2. The chemical pressure estimated from the equation of state is equal to an external physical pressure of 3.6 GPa.
- arXiv:1910.14516 (replaced) [pdf, other]
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Title: Ab initio electron-defect interactions using Wannier functionsJournal-ref: npj Comput. Mater. 6, 17 (2020)Subjects: Materials Science (cond-mat.mtrl-sci)
Computing electron-defect (e-d) interactions from first principles has remained impractical due to computational cost. Here we develop an interpolation scheme based on maximally localized Wannier functions (WFs) to efficiently compute e-d interaction matrix elements. The interpolated matrix elements can accurately reproduce those computed directly without interpolation, and the approach can significantly speed up calculations of e-d relaxation times and defect-limited charge transport. We show example calculations of vacancy defects in silicon and copper, for which we compute the e-d relaxation times on fine uniform and random Brillouin zone grids (and for copper, directly on the Fermi surface) as well as the defect-limited resistivity at low temperature. Our interpolation approach opens doors for atomistic calculations of charge carrier dynamics in the presence of defects.
- arXiv:1911.02560 (replaced) [pdf, other]
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Title: Ideal near-Dirac triple-point semimetal in III-V semiconductor alloysComments: 8 pages, 9 figuresJournal-ref: Phys. Rev. B 101, 125202 (2020)Subjects: Materials Science (cond-mat.mtrl-sci)
Despite the growing interest in topological materials, the difficulty of experimentally synthesizing and integrating them with other materials has been one of the main barriers restricting access to their unique properties. Recent advances in synthesizing metastable phases of crystalline materials can help to overcome this barrier and offer new platforms to experimentally study and manipulate band topology. Because III-V semiconductors have a wide range of functional material applications (including optoelectronic devices, light-emitting diodes, and highly efficient solar cells), and because Bi-doped III-V materials can be synthesized by ion plantation and ion-cutoff methods, we revisit the effect of bismuth substitution in metastable III-V semiconductors. Through first-principles calculation methods, we show that in wurtzite structure III-V materials, Bi substitution can lead to band inversion phenomena and induce nontrivial topological properties. Specifically, we identify that GaBi and InBi are Dirac-Weyl semimetals, characterized by the coexistence of Dirac points and Weyl points, and $\text{GaAs}_{0.5} \text{Bi}_{0.5}$, $\text{GaSb}_{0.5} \text{Bi}_{0.5}$, $\text{InSb}_{0.5} \text{Bi}_{0.5}$ are triple-point semimetals, characterized by two sets of "near Dirac" triple points on the Fermi level. These experimentally-accessible bismuth-based topological semimetals can be integrated into the large family of functional III-V materials for experimental studies of heterostructures and future optoelectronic applications.
Crosses
- arXiv:1805.10543 (cross-list from hep-th) [pdf, other]
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Title: Complex (super)-matrix models with external sources and $q$-ensembles of Chern-Simons and ABJ(M) typeComments: v2: A correction made and several new results added; title changed. 27 pagesSubjects: High Energy Physics - Theory (hep-th); Statistical Mechanics (cond-mat.stat-mech); Mathematical Physics (math-ph)
The Langmann-Szabo-Zarembo (LSZ) matrix model is a complex matrix model with a quartic interaction and two external matrices. The model appears in the study of a scalar field theory on the non-commutative plane. We prove that the LSZ matrix model computes the probability of atypically large fluctuations in the Stieltjes-Wigert matrix model, which is a $q$-ensemble describing $U(N)$ Chern-Simons theory on the three-sphere. The correspondence holds in a generalized sense: depending on the spectra of the two external matrices, the LSZ matrix model either describes probabilities of large fluctuations in the Chern-Simons partition function, in the unknot invariant or in the two-unknot invariant. We extend the result to supermatrix models, and show that a generalized LSZ supermatrix model describes the probability of atypically large fluctuations in the ABJ(M) matrix model.
Fri, 20 Mar 2020
- arXiv:2003.08405 [pdf, other]
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Title: Exploring Hamiltonian Truncation in $\bf{d=2+1}$Comments: 51 pages, 14 figuresSubjects: High Energy Physics - Theory (hep-th); Statistical Mechanics (cond-mat.stat-mech); Strongly Correlated Electrons (cond-mat.str-el); High Energy Physics - Lattice (hep-lat); High Energy Physics - Phenomenology (hep-ph)
We initiate the application of Hamiltonian Truncation methods to solve strongly coupled QFTs in $d=2+1$. By analysing perturbation theory with a Hamiltonian Truncation regulator, we pinpoint the challenges of such an approach and propose a way that these can be addressed. This enables us to formulate Hamiltonian Truncation theory for $\phi^4$ in $d=2+1$, and to study its spectrum at weak and strong coupling. The results obtained agree well with the predictions of a weak/strong self-duality possessed by the theory. The $\phi^4$ interaction is a strongly relevant UV divergent perturbation, and represents a case study of a more general scenario. Thus, the approach developed should be applicable to many other QFTs of interest.
- arXiv:2003.08419 [pdf, other]
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Title: Multiband Quantum Criticality of Polar MetalsSubjects: Strongly Correlated Electrons (cond-mat.str-el)
Motivated by recent experimental realizations of polar metals with broken inversion symmetry, we explore the emergence of strong correlations driven by criticality when the polar transition temperature is tuned to zero. Overcoming previously discussed challenges, we demonstrate a robust mechanism for coupling between the critical mode and electrons in multiband metals. We identify and characterize several novel interacting phases, including non-Fermi liquids, when band crossings close to the Fermi level and present their experimental signatures for three generic types of band crossings.
- arXiv:2003.08425 [pdf, other]
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Title: Taking snapshots of a quantum thermalization process: emergent classicality in quantum jump trajectoriesComments: 5 + 11 pages. 2 + 8 imagesSubjects: Quantum Physics (quant-ph); Statistical Mechanics (cond-mat.stat-mech)
We theoretically investigate the emergence of classical statistical physics in a finite quantum system that is subjected to a quantum measurement process. A random matrix theory approach to non-integrable quantum systems predicts that the set of outcomes of the measurement of a macroscopic observable evolve in time like stochastic variables, whose variance satisfies the celebrated Einstein relation for Brownian diffusion. Our results show how to extend the framework of eigenstate thermalization to the prediction of properties of quantum measurements on an otherwise closed quantum system. We show numerically the validity of the random matrix approach in quantum chain models.
- arXiv:2003.08427 [pdf, other]
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Title: Stress-Induced Dinoflagellate Bioluminescence at the Single Cell LevelAuthors: Maziyar Jalaal, Nico Schramma, Antoine Dode, Helene de Maleprade, Christophe Raufaste, Raymond E. GoldsteinComments: 6 pages, 5 figures plus 4 pages of Supplementary Material with 4 figures; videos available on website of REGSubjects: Soft Condensed Matter (cond-mat.soft); Biological Physics (physics.bio-ph); Fluid Dynamics (physics.flu-dyn); Cell Behavior (q-bio.CB)
One of the characteristic features of many marine dinoflagellates is their bioluminescence, which lights up nighttime breaking waves or seawater sliced by a ship's prow. While the internal biochemistry of light production by these microorganisms is well established, the manner by which fluid shear or mechanical forces trigger bioluminescence is still poorly understood. We report controlled measurements of the relation between mechanical stress and light production at the single-cell level, using high-speed imaging of micropipette-held cells of the marine dinoflagellate $Pyrocystis~lunula$ subjected to localized fluid flows or direct indentation. We find a viscoelastic response in which light intensity depends on both the amplitude and rate of deformation, consistent with the action of stretch-activated ion channels. A phenomenological model captures the experimental observations.
- arXiv:2003.08432 [pdf]
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Title: Optically rewritable memory in a graphene/ferroelectric-photovoltaic heterostructureAuthors: D. Kundys, A. Cascales, A. S. Makhort, H. Majjad, F. Chevrier, B. Doudin, A. Fedrizzi, B. KundysComments: 10 pages, 5 figures, research paperSubjects: Applied Physics (physics.app-ph); Materials Science (cond-mat.mtrl-sci)
Achieving optical operation of logic elements, especially those that involve 2D layers, can open the long sought era of optical computing. However, the efficient optical modulation of the electronic properties of 2D materials including memory effect is currently missing. Here we report a fully optical control of the conductivity of a graphene with write/erase option yet under ultralow optical fluence. The competition between light-induced charge generation in ferroelectric-photovoltaic substrate with subsequent relaxation processes provides the selective photocarrier trapping control affecting the doping of 2D overlayer. These findings open the road to photonic control of 2D devices for all -optical modulators and a variety of all-optical logic circuits, memories and field-effect transistors.
- arXiv:2003.08438 [pdf, other]
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Title: Non-Gaussian Entanglement Renormalization for Quantum FieldsComments: 43 pages, 4 figuresSubjects: High Energy Physics - Theory (hep-th); Strongly Correlated Electrons (cond-mat.str-el); Quantum Physics (quant-ph)
In this work, a non-Gaussian cMERA tensor network for interacting quantum field theories (icMERA) is presented. This consists of a continuous tensor network circuit in which the generator of the entanglement renormalization of the wavefunction is nonperturbatively extended with nonquadratic variational terms. The icMERA circuit nonperturbatively implements a set of scale dependent nonlinear transformations on the fields of the theory, which suppose a generalization of the scale dependent linear transformations induced by the Gaussian cMERA circuit. Here we present these transformations for the case of self-interacting scalar and fermionic field theories. Finally, the icMERA tensor network is fully optimized for the $\lambda \phi^4$ theory in $(1+1)$ dimensions. This allows us to evaluate, nonperturbatively, the connected parts of the two- and four-point correlation functions. Our results show that icMERA wavefunctionals encode proper non-Gaussian correlations of the theory, thus providing a new variational tool to study phenomena related with strongly interacting field theories.
- arXiv:2003.08439 [pdf, other]
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Title: Kibble-Zurek behavior in disordered Chern insulatorsSubjects: Strongly Correlated Electrons (cond-mat.str-el); Disordered Systems and Neural Networks (cond-mat.dis-nn)
Even though no local order parameter in the sense of the Landau theory exists for topological quantum phase transitions in Chern insulators, the highly non-local Berry curvature exhibits critical behavior near a quantum critical point. We investigate the critical properties of its real space analog, the local Chern marker, in weakly disordered Chern insulators. Due to disorder, inhomogeneities appear in the spatial distribution of the local Chern marker. Their size exhibits power-law scaling with the critical exponent matching the one extracted from the Berry curvature of a clean system. We drive the system slowly through such a quantum phase transition. The characteristic size of inhomogeneities in the non-equilibrium post-quench state obeys the Kibble-Zurek scaling. In this setting, the local Chern marker thus does behave in a similar way as a local order parameter for a symmetry breaking second order phase transition. The Kibble-Zurek scaling also holds for the inhomogeneities in the spatial distribution of excitations and of the orbital polarization.
- arXiv:2003.08460 [pdf, other]
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Title: Testing a thermodynamic approach to collective animal behavior in laboratory fish schoolsSubjects: Biological Physics (physics.bio-ph); Soft Condensed Matter (cond-mat.soft); Adaptation and Self-Organizing Systems (nlin.AO)
Collective behaviors displayed by groups of social animals are observed frequently in nature. Understanding and predicting the behavior of complex biological systems is dependent on developing effective descriptions and models. While collective animal systems are characteristically non-equilibrium, we can employ concepts from equilibrium statistical mechanics to motivate the measurement of material-like properties in laboratory animal aggregates. Here, we present results from a new set of experiments that utilize high speed footage of two-dimensional schooling events, particle tracking, and projected static and dynamic light fields to observe and control the behavior of negatively phototaxic fish schools ($\textit{Hemigrammus}$ $\textit{bleheri}$). First, we use static light fields consisting of dark circular regions to produce visual stimuli that confine the schools to a range of areas. We find that the school has a maximum density independent of group size, and that the swim pressure increases linearly with number density, suggesting that unperturbed schools exist on an isotherm. Next, we use dynamic light fields where the radius of the dark region shrinks linearly with time to compress the schools. We find that the effective temperature parameter depends on the compression time and our results are thus consistent with the school having a constant heat flux. These findings provide further evidence for the utility of effective thermodynamic descriptions descriptions of non-equilibrium systems in collective animal behavior.
- arXiv:2003.08463 [pdf]
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Title: Probing Mid-Infrared Phonon Polaritons in the Aqueous PhaseComments: 4 figuresSubjects: Optics (physics.optics); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Applied Physics (physics.app-ph)
Phonon polaritons (PhPs), the collective phonon oscillations with hybridized electromagnetic fields, concentrate optical fields in the mid-infrared frequency range that matches the vibrational modes of molecules. The utilization of PhPs holds the promise for chemical sensing tools and polariton-enhanced nanospectroscopy. However, investigations and innovations on PhPs in the aqueous phase remains stagnant, because of the lack of in situ mid-infrared nano-imaging methods in water. Strong infrared absorption from water prohibits optical delivery and detection in the mid-infrared for scattering-type near-field microscopy. Here, we present our solution: the detection of photothermal responses caused by the excitation of PhPs by liquid phase peak force infrared (LiPFIR) microscopy. Characteristic interference fringes of PhPs in 10B isotope-enriched h-BN were measured in the aqueous phase and their dispersion relationship extracted. LiPFIR enables the measurement of mid-infrared PhPs in the fluid phase, opening possibilities, and facilitating the development of mid-IR phonon polaritonics in water.
- arXiv:2003.08467 [pdf, other]
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Title: Modeling electronic, mechanical, optical and thermal properties of graphene-like BC$_6$N materials: Role of prominent BN-bondsComments: RevTeX, 9 pages with 6 included jpg figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We model monolayer graphene-like materials with BC$_6$N stoichiometry where the bonding between the B and the N atoms plays an important role for their physical and chemical properties. Two types of BC$_6$N are found based on the BN bonds: In the presence of BN bonds, an even number of $\pi$-bonds emerges indicating an aromatic structure and a large direct bandgap appears, while in the absence of BN bonds, an anti-aromatic structure with an odd-number of $\pi$-bonds is found resulting a direct small bandgap. The stress-strain curves shows high elastic moduli and tensile strength of the structures with BN-bonds, compared to structures without BN-bonds. Self-consistent field calculations demonstrate that BC$_6$N with BN-bonds is energetically more stable than structures without BN-bonds due to a strong binding energy between the B and the N atoms, while their phonon dispersion displays that BC$_6$N without BN-bonds has more dynamical stability. Furthermore, all the BC$_6$N structures considered show a large absorption of electromagnetic radiation with polarization parallel to the monolayers in the visible range. Finer detail of the absorption depend on the actual structures of the layers. A higher electronic thermal conductivity and specific heat are seen in BC$_6$N systems caused by hot carrier--assisted charge transport. This opens up a possible optimization for bolometric applications of graphene based material devices.
- arXiv:2003.08470 [pdf, other]
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Title: Imaging domain reversal in an ultrathin van der Waals ferromagnetAuthors: David A. Broadway, Sam C. Scholten, Cheng Tan, Nikolai Dontschuk, Scott E. Lillie, Brett C. Johnson, Guolin Zheng, Zhenhai Wang, Artem R. Oganov, Shangjie Tian, Chenghe Li, Hechang Lei, Lan Wang, Lloyd C. L. Hollenberg, Jean-Philippe TetienneComments: includes SISubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci)
The recent isolation of two-dimensional van der Waals magnetic materials has uncovered rich physics that often differs from the magnetic behaviour of their bulk counterparts. However, the microscopic details of fundamental processes such as the initial magnetization or domain reversal, which govern the magnetic hysteresis, remain largely unknown in the ultrathin limit. Here we employ a widefield nitrogen-vacancy (NV) microscope to directly image these processes in few-layer flakes of magnetic semiconductor vanadium triiodide (VI$_3$). We observe complete and abrupt switching of most flakes at fields $H_c\approx0.5-1$ T (at 5 K) independent of thickness down to two atomic layers, with no intermediate partially-reversed state. The coercive field decreases as the temperature approaches the Curie temperature ($T_c\approx50$ K), however, the switching remains abrupt. We then image the initial magnetization process, which reveals thickness-dependent domain wall depinning fields well below $H_c$. These results point to ultrathin VI$_3$ being a nucleation-type hard ferromagnet, where the coercive field is set by the anisotropy-limited domain wall nucleation field. This work illustrates the power of widefield NV microscopy to investigate magnetization processes in van der Waals ferromagnets, which could be used to elucidate the origin of the hard ferromagnetic properties of other materials and explore field- and current-driven domain wall dynamics.
- arXiv:2003.08471 [pdf, other]
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Title: Scientific AI in materials science: a path to a sustainable and scalable paradigmSubjects: Materials Science (cond-mat.mtrl-sci); Computational Physics (physics.comp-ph)
Recently there has been an ever-increasing trend in the use of machine learning (ML) and artificial intelligence (AI) methods by the materials science, condensed matter physics, and chemistry communities. This perspective article identifies key scientific, technical, and social opportunities that the materials community must prioritize to consistently develop and leverage Scientific AI to provide a credible path towards the advancement of current materials-limited technologies. Here we highlight the intersections of these opportunities with a series of proposed paths forward. The opportunities are roughly sorted from scientific/technical (e.g., development of robust, physically meaningful multiscale material representations) to social (e.g., promoting an AI-ready workforce). The proposed paths forward range from developing new infrastructure and capabilities to deploying them in industry and academia. We provide a brief introduction to AI in materials science and engineering, followed by detailed discussions of each of the opportunities and paths forward.
- arXiv:2003.08478 [pdf]
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Title: Correlation between the tolerance factor and phase transition in Ln4-xLnxNi3O10 (Ln and Ln' = La, Pr and Nd; x = 0, 1, 2 and 3)Subjects: Superconductivity (cond-mat.supr-con); Materials Science (cond-mat.mtrl-sci); Strongly Correlated Electrons (cond-mat.str-el)
We have synthesized a series of the Ruddlesden-Popper nickelate solid solution Ln4-xLn'xNi3O10 (Ln and Ln' = La, Pr and Nd; x = 0, 1, 2 and 3) via the citrate precursor method at different reacting atmospheres. Both the electronic-transport and magnetization measurements on these samples show well-defined phase transitions at temperatures between 135 K and 165 K. These transition temperatures, the room-temperature resistivities, as well as the changes of the Pauli-paramagnetic susceptibilities at the respective phase transitions, strongly correlate with the Goldschmidt tolerance factor t, irrespective of the combination of the magnetic rare-earth ions with unmagnetic La3+. We conclude that these changes of the electronic properties are mostly related to the distortion of the NiO6 octahedra at the phase transition which is strongly correlated with the tolerance factor t, but are rather insensitive to the magnetism of the rare-earth ions Ln3+ and Ln'3+.
- arXiv:2003.08479 [pdf, other]
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Title: Bi-stability of SUDR+K model of epidemics and test kits applied to COVID-19Comments: 6 pages, 7 figures, submitted to Nonlinear DynamicsSubjects: Populations and Evolution (q-bio.PE); Statistical Mechanics (cond-mat.stat-mech); Adaptation and Self-Organizing Systems (nlin.AO); Physics and Society (physics.soc-ph)
Motivated with various responses of world governments to COVID-19, here we develop a toy model of the dependence epidemics spreading on the availability of tests for disease. Our model, that we call SUDR+K, is based on usual SIR model, but it splits the total fraction of infected individuals into two components: those that are undetected and those that are detected through tests. Moreover, we assume that available tests increase at a constant rate from the beginning of epidemics but are consumed to detect infected individuals. Strikingly we find a bi-stable behavior between a phase with a giant fraction of infected and a phase with a very small fraction. We show that the separation between these two regimes is governed by a match between the rate of testing and a rate of infection spread at given time. We also show that the existence of two phases does not depend on the mathematical choice of the form of the term describing the rate at which undetected individuals are tested and detected. Presented research implies that a vigorous early testing activity, before the epidemics enters into its giant phase, can potentially keep epidemics under control, and that even a very small change in rate of testing can increase or decrease the size of the whole epidemics of various orders of magnitude. For the real application of realistic model to ongoing epidemics, we would gladly collaborate with field epidemiologists in order to develop quantitative models of testing process.
- arXiv:2003.08482 [pdf, other]
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Title: Tumbling with a Limp: Local Asymmetry in Water's Hydrogen Bond Network and its ConsequencesSubjects: Disordered Systems and Neural Networks (cond-mat.dis-nn); Chemical Physics (physics.chem-ph)
Ab initio molecular dynamics simulations of liquid water under equilibrium ambient conditions, together with a novel energy decomposition analysis, have recently shown that a substantial fraction of water molecules exhibit a significant asymmetry between the strengths of the two donor and/or the two acceptor interactions. We refer to this recently unraveled aspect as the "local asymmetry in the hydrogen bond network". We discuss how this novel aspect was first revealed, and provide metrics that can be consistently employed on simulated water trajectories to quantify this local heterogeneity in the hydrogen bond network and its dynamics. We then discuss the static aspects of the asymmetry, pertaining to the frozen geometry of liquid water at any given instant of time and the distribution of hydrogen bond strengths therein, and also its dynamic characteristics pertaining to how fast this asymmetry decays and the kinds of molecular motions responsible for this decay. Following this we discuss the spectroscopic manifestations of this asymmetry, from ultrafast X-ray absorption spectra to infrared spectroscopy and down to the much slower terahertz regime. Finally, we discuss the implications of these findings in a broad context and its relation to the current notions about the structure and dynamics of liquid water.
- arXiv:2003.08488 [pdf, ps, other]
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Title: Magnetic Fabry-Pérot interferometer for valley filtering in a honeycomb-dice modelComments: 12 pages, 13 figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Here we theoretically investigate the valley-dependent transmission of particles through a combined electric and magnetic barrier in the $\alpha-T_3$ model which interpolates between the honeycomb and the dice lattices. We put forward that the combination of the Fabry-P\'erot interferences and the magnetic field leads to a perfect transmission for one valley and a suppression of the transmission for the other valley. When only one of the barriers (magnetic or electric) is present, no valley polarized current can be produced. By tuning the Fermi energy, this valley-dependent peculiar behavior can be used as valley filtering. Our results show that highly efficient valley filtering with maximum conductivity and polarization can be achieved by controlling the value of the magnetic field and the electric barrier width and height.
- arXiv:2003.08498 [pdf, ps, other]
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Title: Directed transport of suspended ferromagnetic nanoparticles under both gradient and uniform magnetic fieldsComments: 14 pages, 5 figuresSubjects: Soft Condensed Matter (cond-mat.soft)
The suspended ferromagnetic particles subjected to the gradient and uniform magnetic fields experience both the translational force generated by the field gradient and the rotational torque generated by the fields strengths. Although the uniform field does not contribute to the force, it nevertheless influences the translational motion of these particles. This occurs because the translational force depends on the direction of the particle magnetization, which in turn depends on the fields strengths. To study this influence, a minimal set of equations describing the coupled translational and rotational motions of nanosized ferromagnetic particles is introduced and solved in the low Reynolds number approximation. Trajectory analysis reveals that, depending on the initial positions of nanoparticles, there exist four regimes of their directed transport. The intervals of initial positions that correspond to different dynamical regimes are determined, their dependence on the uniform magnetic field is established, and strong impact of this field on the directed transport is demonstrated. The ability and efficiency of the uniform magnetic field to control the separation of suspended ferromagnetic nanoparticles is also discussed.
- arXiv:2003.08506 [pdf]
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Title: Superconducting Dome in Nd$_{1-x}$Sr$_x$NiO$_2$ Infinite Layer FilmsAuthors: Danfeng Li, Bai Yang Wang, Kyuho Lee, Shannon P. Harvey, Motoki Osada, Berit H. Goodge, Lena F. Kourkoutis, Harold Y. HwangComments: 15 pages (including Supplemental Material), 5 figures (including 1 supplemental figure)Subjects: Superconductivity (cond-mat.supr-con); Materials Science (cond-mat.mtrl-sci)
We report the phase diagram of Nd$_{1-x}$Sr$_x$NiO$_2$ infinite layer thin films grown on SrTiO$_3$. A superconducting dome spanning $0.125 < x < 0.25$ is found, remarkably similar to cuprates, albeit over a narrower doping window. However, while cuprate superconductivity is bounded by an insulator for underdoping and a metal for overdoping, here we observe weakly insulating behavior on either side of the dome. Furthermore, the normal state Hall coefficient is always small and proximate to a continuous zero crossing in doping and in temperature, in contrast to the $\sim 1/x$ dependence observed for cuprates. This suggests the presence of both electron- and hole-like bands, consistent with band structure calculations.
- arXiv:2003.08524 [pdf, other]
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Title: Towards elucidation of zero-temperature criticality of Ising model on 2d DTComments: 20 pages, 4 figures; minor corrections; Introduction and Discussion expandedJournal-ref: Phys. Rev. D 101, 106019 (2020)Subjects: High Energy Physics - Theory (hep-th); Statistical Mechanics (cond-mat.stat-mech); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Lattice (hep-lat)
We study the zero-temperature criticality of the Ising model on two-dimensional dynamical triangulations to contemplate its physics. As it turns out, an inhomogeneous nature of the system yields an interesting phase diagram and the physics at the zero temperature is quite sensitive about how we cool down the system. We show the existence of a continuous parameter that characterizes the way we approach the zero-temperature critical point and it may enter in a critical exponent.
- arXiv:2003.08531 [pdf, other]
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Title: Evolution of the structural transition in Mo$_{1-x}$W$_{x}$Te$_{2}$Authors: John A. Schneeloch, Yu Tao, Chunruo Duan, Masaaki Matsuda, Adam A. Aczel, Jaime A. Fernandez-Baca, Guangyong Xu, Jörg C. Neuefeind, Junjie Yang, Despina LoucaComments: supplement in separate fileSubjects: Materials Science (cond-mat.mtrl-sci)
The composition dependence of the structural transition between the monoclinic 1T$^{\prime}$ and orthorhombic T$_{d}$ phases in the Mo$_{1-x}$W$_{x}$Te$_{2}$ Weyl semimetal was investigated by elastic neutron scattering on single crystals up to $x \approx 0.54$. First observed in MoTe$_{2}$, the transition from T$_{d}$ to 1T$^{\prime}$ is accompanied by an intermediate pseudo-orthorhombic phase, T$_{d}^{*}$. Upon doping with W the T$_{d}^{*}$ phase vanishes by $x \approx 0.34$. Above this concentration, a phase coexistence behavior with both T$_{d}$ and 1T$^{\prime}$ is observed, instead. The interlayer in-plane positioning parameter, $\delta$, which relates to the 1T$^{\prime}$ $\beta$ angle, decreases with temperature as well as with W substitution indicating strong anharmonicity of the layer displacements. The temperature width of the phase coexistence remains almost constant up to $x \approx 0.54$, in contrast to the broadening reported with applying pressure.
- arXiv:2003.08535 [pdf, ps, other]
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Title: Two-dimensional square lattice polonium stabilized by the spin-orbit couplingAuthors: Shota OnoComments: 4 pages, 6 figuresSubjects: Materials Science (cond-mat.mtrl-sci)
Polonium is known as the only simple metal that has the simple cubic (SC) lattice in three dimension. There is a debate about whether the stabilized SC structure is attributed to the scalar relativistic effect or the spin-orbit coupling (SOC). Here, we study another phase, two-dimensional (2D) polonium (poloniumene), by performing density-functional theory calculations. We show that the 2D polonium has the square lattice structure as its ground state and demonstrate that the SOC (beyond the scalar relativistic approximation) suppresses the Peierls instability and is necessary to obtain no imaginary phonon frequencies over the Brillouin zone.
- arXiv:2003.08548 [pdf, ps, other]
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Title: Refined Nonequilibrium Thermodynamic Bounds for General Open Quantum ProcessesComments: 6 pages, two-columnSubjects: Statistical Mechanics (cond-mat.stat-mech); Quantum Physics (quant-ph)
We show how various thermodynamic bounds for nonequilibrium quantum processes can be improved and recovered from one simple formula based on the operator concavity of the logarithmic function.
- arXiv:2003.08557 [pdf, ps, other]
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Title: Thermodynamic uncertainty relation for open quantum systemsAuthors: Yoshihiko HasegawaComments: 8 pages, 4 figures; 6 pages of supplemental material with 1 figureSubjects: Statistical Mechanics (cond-mat.stat-mech); Quantum Physics (quant-ph)
We derive a thermodynamic uncertainty relation for general open quantum systems. Open quantum dynamics can be described by a joint unitary evolution on a composite system consisting of system and environment. By considering the environmental state after the interaction, we bound counting observables on the environment by a generalized dynamical activity, which is a quantum analogue of the quantity in classical Markov processes. Remarkably, our relation holds for any open quantum systems, any counting observables, and any initial states. We apply our relation to the continuous measurement on open quantum systems and the quantum walk to find that the quantumness of the system can enhance the precision. Moreover, we can make the lower bound arbitrarily small by employing different continuous measurements.
- arXiv:2003.08566 [pdf, ps, other]
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Title: Symplectic ferromagnetism and phase transitions in multi-component fermionic systemsSubjects: Quantum Gases (cond-mat.quant-gas)
In this paper, we study the itinerant ferromagnetic phase in multi-component fermionic systems with symplectic (Sp(4), or isomorphically SO(5)) symmetry. Two different microscopic models have been considered and an effective field theory has been proposed to study the critical behavior of the nonmagnetism-magnetism phase transition. It has been shown that such systems exhibit intriguing ferromagnetism and critical behavior that different from those in spin-$\frac 12$ fermionic systems, or in high-spin systems with SU(N) symmetry. An extension of our results to higher spin systems with Sp(2N) symmetry has also been discussed.
- arXiv:2003.08575 [pdf]
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Title: Predictability as a probe of manifest and latent physics: the case of atomic scale structural, chemical, and polarization behaviors in multiferroic Sm-doped BiFeO3Authors: Maxim Ziatdinov, Nicole Creange, Xiaohang Zhang, Anna Morozovska, Eugene Eliseev, Rama K. Vasudevan, Ichiro Takeuchi, Chris Nelson, Sergei V. KalininSubjects: Materials Science (cond-mat.mtrl-sci)
Predictability of a certain effect or phenomenon is often equated with the knowledge of relevant physical laws, typically understood as a functional or numerically-derived relationship between the observations and known states of the system. Correspondingly, observations inconsistent with prior knowledge can be used to derive new knowledge on the nature of the system or indicate the presence of yet unknown mechanisms. Here we explore the applicability of Gaussian Processing (GP) to establish predictability and uncertainty of local behaviors from multimodal observations, providing an alternative to this classical paradigm. Using atomic-resolution Scanning Transmission Electron Microscopy (STEM) of multiferroic Sm-doped BiFeO3 across a broad composition range, we directly visualize the atomic structure and structural, physical, and chemical order parameter fields for the material. GP regression is used to establish the predictability of the local polarization field from different groups of parameters, including the adjacent polarization values and several combinations of physical and chemical descriptors, including lattice parameters, column intensities, etc. We observe that certain elements of materials domain structure including charged and uncharged domain walls and interfaces with the substrate are best predicted with specific combinations of descriptors, and this predictability and their associated uncertainties are consistent across the composition series. The associated generative physical mechanisms are discussed. We argue that predictability and uncertainty in observational data offers a new pathway to probe the physics of condensed matter systems from multimodal local observations.
- arXiv:2003.08596 [pdf, other]
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Title: Length-scale independent skyrmion and meron Hall anglesComments: 4 pages, 1 figureSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Strongly Correlated Electrons (cond-mat.str-el)
Motivated by the recent observation [Zeissler {\em et al.}, Nature Comm. 11, 428 (2020)] of enigmatic radius-independent skyrmion Hall angle in chiral magnets, we derive skyrmion Hall angle based on the recent solution of skyrmions characterized by the sole length scale determined with the Dzyaloshinskii-Moriya interaction strength and applied magnetic field. Our analysis finds length-scale and input current-density independent skyrmion Hall angle, in agreement with experiments. With the application of tunable current along mutually perpendicular directions, this property enables us to propose an experimental setup by which the transverse motion of a skyrmion can be restricted so that the skyrmion can only traverse longitudinally. We further find the length-scale and input-current density independent Hall angles for merons where their transverse motion will be opposite depending on whether the spin at their centers are up or down, in agreement with an experiment.
- arXiv:2003.08602 [pdf, ps, other]
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Title: Cavity-induced Fulde-Ferrell-Larkin-Ovchinnikov superfluids of ultracold Fermi gasesComments: 6 pages, 3 figuresJournal-ref: Phys. Rev. A 101, 023612 (2020)Subjects: Quantum Gases (cond-mat.quant-gas)
Motivated by recent experimental advances in ultracold atomic gases placed in cavities, we study the influence of the atom-cavity coupling on the Fermi gases trapped in optical lattices. By adiabatic elimination of the cavity photon field, the atom-cavity coupling gives rise to effective long-range interactions. It results in a variety of two-body scattering processes, during which the atomic pairs can acquire an additional center-of-mass momentum. This reveals the possibility of Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) superfluids in which the atomic pairing momentum is nonzero. By inspecting the phase diagram at the mean-field level, we confirm that the FFLO superfluid phase coexists with the zero-momentum pairing, and is the ground state that hosts the lowest energy. Furthermore, the order parameter characterizing the nonzero-momentum pairing does not vanish as long as the cavity-induced interaction is present.
- arXiv:2003.08629 [pdf]
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Title: Certifying the intrinsic character of a constitutive law for semi-crystalline polymers: a probation testAuthors: Stéphane André (UL), Simon Becker (LEMTA), Camille Noûs, Laurent Farge (LEMTA), Alain Delconte (CRAN)Subjects: Soft Condensed Matter (cond-mat.soft); Computational Physics (physics.comp-ph)
A study of methodological nature demonstrates the efficiency of a probation test allowing for the intrinsic character of a rheological constitutive law to be assessed. Such a law is considered here for Semi-Crystalline Polymers exhibiting necking and for large deformation. In the framework of a $(\dot\sigma, \sigma, \dot\varepsilon, \varepsilon)$ behavior's law, tensile experiments conducted at an imposed constant strain rate $\dot\varepsilon_0$ bring true stress responses from which constitutive (material) parameters can be identified from Model-Based Metrology concepts. The same experiment repeated at various strain rates gives then access to the dependence of the non-elastic parameters on the strain rate. Then the intrinsic law is tested severely by considering a new set of experiments carried out for constant displacement rates of the grips. In that case, the specimens show local strain rates which evolve strongly during the test (by a factor of 5-10 here). The parameter identification process requires then the introduction of the exact realized input strain and strain-rate command into the model. Accounting for strain rate dependency requires additionally the knowledge of the preliminary identified strain rate dependence of the non-elastic constitutive parameters for good predictions of the experimental response directly. This is what is proven here. The conclusion speaks in favor of a possible upgrade of international standards for the mechanical characterization of polymers based on constant strain-rate tensile tests and properly applied model-based metrology.
- arXiv:2003.08651 [pdf]
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Title: Energy Transfer within the Hydrogen Bonding Network of Water Following Resonant Terahertz ExcitationAuthors: Hossam Elgabarty, Tobias Kampfrath, Douwe Jan Bonthuis, Vasileios Balos, Naveen Kumar Kaliannan, Philip Loche, Roland R. Netz, Martin Wolf, Thomas D. Kühne, Mohsen SajadiSubjects: Soft Condensed Matter (cond-mat.soft); Chemical Physics (physics.chem-ph)
Energy dissipation in water is very fast and more efficient than in many other liquids. This behavior is commonly attributed to the intermolecular interactions associated with hydrogen bonding. Here, we investigate the dynamic energy flow in the hydrogen-bond network of liquid water by a pump-probe experiment. We resonantly excite intermolecular degrees of freedom with ultrashort single-cycle terahertz pulses and monitor its Raman response. By using ultrathin sample-cell windows, a background-free bipolar signal whose tail relaxes mono-exponentially is obtained. The relaxation is attributed to the molecular translational motions, using complementary experiments, force-field and ab initio molecular dynamics simulations. They reveal an initial coupling of the terahertz electric field to the molecular rotational degrees of freedom whose energy is rapidly transferred, within the excitation pulse duration, to the restricted-translational motion of neighboring molecules. This rapid energy transfer may be rationalized by the strong anharmonicity of the intermolecular interactions.
- arXiv:2003.08662 [pdf, other]
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Title: Slow time scales in a dense vibrofluidized granular materialSubjects: Soft Condensed Matter (cond-mat.soft); Statistical Mechanics (cond-mat.stat-mech)
Modeling collective motion in non-conservative systems, such as granular materials, is difficult since a general microscopic-to-macroscopic approach is not available: there is no Hamiltonian, no known stationary densities in phase space, not a known small set of relevant variables. Phenomenological coarse-grained models are a good alternative, provided that one has individuated a few slow observables and collected a sufficient amount of data for their dynamics. Here we study the case of a vibrofluidized dense granular material. The experimental study of a tracer, dispersed into the media, showed the evidence of many time scales: fast ballistic, intermediate caged, slow superdiffusive, very slow diffusive. A numerical investigation has demonstrated that tracer's superdiffusion is related to slow rotating drifts of the granular medium. Here we offer a deeper insight into the slow scales of the granular medium, and propose a new phenomenological model for such a "secular" dynamics. Based upon the model for the granular medium, we also introduce a model for the tracer (fast and slow) dynamics, which consists in a stochastic system of equations for three coupled variables, and is therefore more refined and successful than previous models.
- arXiv:2003.08667 [pdf, other]
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Title: The Unreasonable Effectiveness of the Nallet ModelAuthors: Doru ConstantinSubjects: Soft Condensed Matter (cond-mat.soft)
In 1993, Nallet, Laversanne and Roux put forward a simplified model for the intensity scattered by lamellar phases, which was nonetheless very successfully used in fitting experimental results, especially those obtained with powder systems. I argue that the success as well as the simple expression of the model result from an approximate integration over sample orientation, resulting from an implicit integration over the scattering vector component normal to the director.
- arXiv:2003.08669 [pdf, other]
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Title: Understanding real-time time-dependent density-functional theory simulations of ultrafast laser-induced dynamics in organic moleculesSubjects: Materials Science (cond-mat.mtrl-sci); Chemical Physics (physics.chem-ph)
Real-time time-dependent density functional theory, in conjunction with the Ehrenfest molecular dynamics scheme, is becoming a popular methodology to investigate ultrafast phenomena on the nanoscale. Thanks to recent developments, it is also possible to explicitly include in the simulations a time-dependent laser pulse, thereby accessing the transient excitation regime. However, the complexity entailed in these calculations calls for in-depth analysis of the accessible yet approximate (either "dressed" or "bare") quantities in order to evaluate their ability to provide us with a realistic picture of the simulated processes. In this work, we analyze the ultrafast dynamics of three small molecules (ethylene, benzene, and thiophene) excited by a resonant laser pulse in the framework of the adiabatic local-density approximation. The electronic response to the laser perturbation in terms of induced dipole moment and excited-state population is compared to the results given by an exactly solvable two-level model. In this way, we can interpret the charge-carrier dynamics in terms of simple estimators, such as the number of excited electrons. From the computed transient absorption spectra we unravel the appearance of nonlinear effects such as excited-state absorption and vibronic coupling. In this way, we observe that the laser excitation affects the vibrational spectrum by enhancing the anharmonicities therein while the coherent vibrational motion contributes to stabilize the electronic excitation already within a few tens of femtoseconds.
- arXiv:2003.08670 [pdf, other]
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Title: Semi-analytic approximate stability selection for correlated data in generalized linear modelsComments: 32 pages, 7 figuresSubjects: Machine Learning (stat.ML); Disordered Systems and Neural Networks (cond-mat.dis-nn); Statistical Mechanics (cond-mat.stat-mech); Machine Learning (cs.LG); Methodology (stat.ME)
We consider the variable selection problem of generalized linear models (GLMs). Stability selection (SS) is a promising method proposed for solving this problem. Although SS provides practical variable selection criteria, it is computationally demanding because it needs to fit GLMs to many re-sampled datasets. We propose a novel approximate inference algorithm that can conduct SS without the repeated fitting. The algorithm is based on the replica method of statistical mechanics and vector approximate message passing of information theory. For datasets characterized by rotation-invariant matrix ensembles, we derive state evolution equations that macroscopically describe the dynamics of the proposed algorithm. We also show that their fixed points are consistent with the replica symmetric solution obtained by the replica method. Numerical experiments indicate that the algorithm exhibits fast convergence and high approximation accuracy for both synthetic and real-world data.
- arXiv:2003.08672 [pdf, other]
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Title: Role of Nambu-Goldstone modes in the fermionic superfluid point contactAuthors: Shun UchinoComments: 9 pages, 2 figuresSubjects: Quantum Gases (cond-mat.quant-gas)
In fermionic superfluids that are charge neutral, Nambu-Goldstone (NG) modes also known as Anderson-Bogoliubov modes emerge as a result of spontaneous symmetry breaking. Here, we discuss DC transport properties of such NG modes through a quantum point contact. We show that contrary to a naive view that enhancement of the phase stiffness may suppress transport of the NG modes, there must be an anomalous contribution that survives at low temperature. This contribution originates from the conversion process between the condensate and NG mode. We find that within the BCS regime the anomalous contribution is enhanced with increasing channel transmittance and attractive interaction, and leads to a temperature-dependent Lorenz number and absence of the bunching effect in current noise.
- arXiv:2003.08674 [pdf, other]
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Title: Exact coarse-graining preserves entropy production out of equilibriumSubjects: Statistical Mechanics (cond-mat.stat-mech)
The entropy production rate associated to broken time-reversal symmetry provides an essential characterization of nano-systems out of equilibrium, from driven colloidal particles to molecular motors. Limited access to the dynamical states is generally expected to hinder the correct estimation of this observable. Here we show how memoryless jump processes can be coarse-grained exactly preserving its average and fluctuations at stationarity. This supports univocal applicability of fluctuation theorems for entropy and allows inference of the genuine thermodynamics together with inaccessible process details.
- arXiv:2003.08682 [pdf, other]
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Title: Magnetism and Néel skyrmion dynamics in GaV$_{4}$S$_{8-y}$Se$_{y}$Authors: T. J. Hicken, S. J. R. Holt, K. J. A. Franke, Z. Hawkhead, A. Štefančič, M. N. Wilson, M. Gomilšek, B. M. Huddart, S. J. Clark, M. R. Lees, F. L. Pratt, S. J. Blundell, G. Balakrishnan, T. LancasterComments: 6 pages, 4 figuresSubjects: Strongly Correlated Electrons (cond-mat.str-el)
We present an investigation of the influence of low-levels of chemical substitution on the magnetic ground state and N\'{e}el skyrmion lattice (SkL) state in GaV$_4$S$_{8-y}$Se$_y$, where $y =0, 0.1, 7.9$, and $8$. Muon-spin spectroscopy ($\mu$SR) measurements on $y=0$ and $0.1$ materials reveal the magnetic ground state consists of microscopically coexisting incommensurate cycloidal and ferromagnetic environments, while chemical substitution leads to the growth of localized regions of increased spin density. $\mu$SR measurements of emergent low-frequency skyrmion dynamics show that the SkL exists under low-levels of substitution at both ends of the series. Skyrmionic excitations persist to temperatures below the equilibrium SkL in substituted samples, suggesting the presence of skyrmion precursors over a wide range of temperatures.
- arXiv:2003.08694 [pdf, ps, other]
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Title: Resolving complex spin textures in nanoparticles by magnetic neutron scatteringAuthors: Laura G. Vivas, Rocio Yanes, Dmitry Berkov, Sergey Erokhin, Mathias Bersweiler, Dirk Honecker, Philipp Bender, Andreas MichelsComments: 6 pages, 3 figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
In the quest to image the three-dimensional magnetization structure we show that the technique of magnetic small-angle neutron scattering (SANS) is highly sensitive to the details of the internal spin structure of nanoparticles. By combining SANS with numerical micromagnetic computations we study the transition from single-domain to multi-domain behavior in nanoparticles and its implications for the ensuing magnetic SANS cross section. Above the critical single-domain size we find that the cross section and the related correlation function cannot be described anymore with the uniform particle model, resulting e.g. in deviations from the well-known Guinier law. We identify a clear signature for the occurrence of a vortex-like spin structure at remanence. The micromagnetic approach to magnetic SANS bears great potential for future investigations, since it provides fundamental insights into the mesoscale magnetization profile of nanoparticles.
- arXiv:2003.08698 [pdf, other]
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Title: Tunable Order of Helically Confined ChargesComments: 10 pages, 6 figuresSubjects: Classical Physics (physics.class-ph); Other Condensed Matter (cond-mat.other); Adaptation and Self-Organizing Systems (nlin.AO)
We investigate a system of equally charged Coulomb-interacting particles confined to a toroidal helix in the presence of an external electric field. Due to the confinement, the particles experience an effective interaction that oscillates with the particle distance and allows for the existence of stable bound states, despite the purely repulsive character of the Coulomb interaction. We design an order parameter to classify these bound states and use it to identify a structural crossover of the particle order, occurring when the electric field strength is varied. Amorphous particle configurations for a vanishing electric field and crystalline order in the regime of a strong electric field are observed. We study the impact of parameter variations on the particle order and conclude that the crossover occurs for a wide range of parameter values and even holds for different helical systems.
- arXiv:2003.08708 [pdf, other]
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Title: Three-phase fluid coexistence in heterogenous slitsComments: 5 pagesJournal-ref: Phys. Rev. Lett. 124, 115701 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Statistical Mechanics (cond-mat.stat-mech)
We study the competition between local (bridging) and global condensation of fluid in a chemically heterogeneous capillary slit made from two parallel adjacent walls each patterned with a single stripe. Using a mesoscopic modified Kelvin equation, which determines the shape of the menisci pinned at the stripe edges in the bridge phase, we determine the conditions under which the local bridging transition precedes capillary condensation as the pressure (or chemical potential) is increased. Provided the contact angle of the stripe is less than that of the outer wall we show that triple points, where evaporated, locally condensed and globally condensed states all coexist are possible depending on the value of the aspect ratio $a=L/H$ where $H$ is the stripe width and $L$ the wall separation. In particular, for a capillary made from completely dry walls patterned with completely wet stripes the condition for the triple point occurs when the aspect ratio takes its maximum possible value $8/\pi$. These predictions are tested using a fully microscopic classical Density Functional Theory and shown to be remarkably accurate even for molecularly narrow slits. The qualitative differences with local and global condensation in heterogeneous cylindrical pores are also highlighted.
- arXiv:2003.08709 [pdf, other]
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Title: Atom-Photon Spin-Exchange Collisions Mediated by Rydberg DressingComments: 6+6 pages, 4+3 figuresSubjects: Quantum Physics (quant-ph); Quantum Gases (cond-mat.quant-gas); Optics (physics.optics)
We show that photons propagating through a Rydberg-dressed atomic ensemble can exchange its spin state with a single atom. Such a spin-exchange collision exhibits both dissipative and coherent features, depending on the interaction strength. For strong interaction, the collision dissipatively drives the system into an entangled dark state of the photon with an atom. In the weak interaction regime, the scattering coherently flips the spin of a single photon in the multi-photon input pulse, demonstrating a generic single-photon subtracting process. An analytic analysis of this process reveals a universal trade-off between efficiency and purity of the extracted photon, which applies to a wide class of single-photon subtractors. We show that such a trade-off can be optimized by adjusting the scattering rate under a novel phase-matching condition.
- arXiv:2003.08710 [pdf, other]
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Title: Noise and full counting statistics of a Cooper pair splitterComments: 15 pages, 6 figuresJournal-ref: Phys. Rev. B 101, 205422 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Superconductivity (cond-mat.supr-con)
We investigate theoretically the noise and the full counting statistics of electrons that are emitted from a superconductor into two spatially separated quantum dots by the splitting of Cooper pairs and further on collected in two normal-state electrodes. With negatively-biased drain electrodes and a large superconducting gap, the dynamics of the Cooper pair splitter can be described by a Markovian quantum master equation. Using techniques from full counting statistics, we evaluate the electrical currents, their noise power spectra, and the power-power correlations in the output leads. The current fluctuations can be attributed to the competition between Cooper pair splitting and elastic cotunneling between the quantum dots via the superconductor. In one regime, these processes can be clearly distinguished in the cross-correlation spectrum with peaks and dips appearing at characteristic frequencies associated with elastic cotunneling and Cooper pair splitting, respectively. We corroborate this interpretation by analyzing the charge transport fluctuations in the time domain, specifically by investigating the $g^{(2)}$-function of the output currents. Our work identifies several experimental signatures of the fundamental transport processes involved in Cooper pair splitting and provides specific means to quantify their relative strengths. As such, our results may help guide and interpret future experiments on current fluctuations in Cooper pair splitters.
- arXiv:2003.08716 [pdf, ps, other]
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Title: Ultrafast polarization switching in ferroelectricsComments: Latex file, 13 pages, 7 figuresJournal-ref: Phys. Rev. Res. 1, 033136 (2019)Subjects: Other Condensed Matter (cond-mat.other); Applied Physics (physics.app-ph)
A method of ultrafast switching of ferroelectric polarization is suggested. The method is based on the interaction of a ferroelectric sample with the feedback field of a resonator in which the sample is inserted. The polarization reversal time can be of order of femtoseconds. The polarization switching produces a coherent electromagnetic pulse.
- arXiv:2003.08728 [pdf, ps, other]
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Title: Anisotropy of the Upper Critical Field in the Heavy-Fermion Superconductor UTe2 under PressureAuthors: Georg Knebel, Motoi Kimata, Michal Vališka, Fuminori Honda, Dexin Li, Daniel Braithwaite, Gérard Lapertot, William Knafo, Alexandre Pourret, Yoshiki J. Sato, Yusei Shimizu, Takumi Kihara, Jean-Pascal Brison, Jacques Flouquet, Dai AokiComments: 5 pages and 4 figures, supplemental material: 9 figuresJournal-ref: J. Phys. Soc. Jpn. 89, 053707 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el)
We studied the anisotropy of the superconducting upper critical field $H_{\rm c2}$ in the heavy-fermion superconductor UTe$_2$ under hydrostatic pressure by magnetoresistivity measurements. In agreement with previous experiments we confirm that superconductivity disappears near a critical pressure $p_{\rm c} \approx 1.5$~GPa, and a magnetically ordered state appears. The unusual $H_{\rm c2}(T)$ at low temperatures for $H \parallel a$ suggests that the multiple superconducting phases which appear under pressure have quite different $H_{\rm c2}$. For a field applied along the hard magnetization $b$ axis $H_{\rm c2} (0)$ is glued to the metamagnetic transition $H_{\rm m}$ which is suppressed near $p_{\rm c}$. The suppression of $H_{\rm m}$ with pressure follows the decrease of temperature $T_{\chi}^{\rm max}$, at the maximum in the susceptibility along $b$. The strong reinforcement of $H_{\rm c2}$ at ambient pressure for $H \parallel b$ above 16~T is rapidly suppressed under pressure due to the increase of $T_{\rm sc}$ and the decrease of $H_{\rm m}$. The change in the hierarchy of the anisotropy of $H_{\rm c2}(0)$ on approaching $p_{\rm c}$ points out that the $c$ axis becomes the hard magnetization axis.
- arXiv:2003.08739 [pdf, other]
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Title: Quantum driven proton diffusion in brucite-like minerals under high pressureSubjects: Materials Science (cond-mat.mtrl-sci)
We investigate the elementary steps at the microscopic level for proton diffusion in brucite under high pressure, which results from a complex interplay between two processes: the O-H reorientations motion around the $\mathbf c$ axis and O-H covalent bond dissociations. First-principle path-integral molecular dynamics simulations reveal that the increasing pressure tends to lock the former motion, while, in contrast, it activates the latter which is mainly triggered by nuclear quantum effects. These two competing effects therefore give rise to a pressure sweet spot for proton diffusion within the mineral. In brucite \ce{Mg(OH)2}, proton diffusion reaches a maximum for pressures close to 70GPa, while the structurally similar portlandite \ce{Ca(OH)2} never shows proton diffusion within the pressure range and time scale that we explored. We analyze the different behaviors of brucite and portlandite, which might constitute two prototypes for other minerals with the same structure.
- arXiv:2003.08749 [pdf]
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Title: Toward Enabling a Reliable Quality Monitoring System for Additive Manufacturing Process using Deep Convolutional Neural NetworksSubjects: Computer Vision and Pattern Recognition (cs.CV); Materials Science (cond-mat.mtrl-sci); Machine Learning (cs.LG); Image and Video Processing (eess.IV); Machine Learning (stat.ML)
Additive Manufacturing (AM) is a crucial component of the smart industry. In this paper, we propose an automated quality grading system for the AM process using a deep convolutional neural network (CNN) model. The CNN model is trained offline using the images of the internal and surface defects in the layer-by-layer deposition of materials and tested online by studying the performance of detecting and classifying the failure in AM process at different extruder speeds and temperatures. The model demonstrates the accuracy of 94% and specificity of 96%, as well as above 75% in three classifier measures of the Fscore, the sensitivity, and precision for classifying the quality of the printing process in five grades in real-time. The proposed online model adds an automated, consistent, and non-contact quality control signal to the AM process that eliminates the manual inspection of parts after they are entirely built. The quality monitoring signal can also be used by the machine to suggest remedial actions by adjusting the parameters in real-time. The proposed quality predictive model serves as a proof-of-concept for any type of AM machines to produce reliable parts with fewer quality hiccups while limiting the waste of both time and materials.
- arXiv:2003.08785 [pdf, other]
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Title: Energy Resolution and Neutron Flux of the 4SEASONS Spectrometer RevisitedAuthors: Ryoichi Kajimoto, Mitsutaka Nakamura, Kazuki Iida, Kazuya Kamazawa, Kazuhiko Ikeuchi, Yasuhiro Inamura, Motoyuki IshikadoComments: 9 pages, 4 figures, Proceedings of ICANS-XXIIISubjects: Instrumentation and Detectors (physics.ins-det); Materials Science (cond-mat.mtrl-sci)
The elastic energy resolution, integrated intensity, and peak intensity of the direct-geometry neutron chopper spectrometer 4SEASONS at Japan Proton Accelerator Research Complex (J-PARC) were re-investigated. This was done with respect to the incident energy and the rotation speed of the Fermi chopper using incoherent scattering of vanadium and simple analytical formulas. The model calculations reproduced the observed values satisfactorily. The present work should be useful for estimating in instrument performance in experiments.
- arXiv:2003.08815 [pdf, other]
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Title: Is friction essential for dilatancy and shear jamming in granular matter?Subjects: Statistical Mechanics (cond-mat.stat-mech); Soft Condensed Matter (cond-mat.soft)
Granular packings display the remarkable phenomenon of dilatancy [1], wherein their volume increases upon shear deformation. Conventional wisdom and previous results suggest that dilatancy, as also the related phenomenon of shear-induced jamming, requires frictional interactions [2, 3]. Here, we investigate the occurrence of dilatancy and shear jamming in frictionless packings. We show that the existence of isotropic jamming densities {\phi}j above the minimal density, the J-point density {\phi}J [4, 5], leads both to the emergence of shear-induced jamming and dilatancy. Packings at {\phi}J form a significant threshold state into which systems evolve in the limit of vanishing pressure under constant pressure shear, irrespective of the initial jamming density {\phi}j. While packings for different {\phi}j display equivalent scaling properties under compression [6], they exhibit striking differences in rheological behaviour under shear. The yield stress under constant volume shear increases discontinuously with density when {\phi}j > {\phi}J, contrary to the continuous behavior in generic packings that jam at {\phi}J [4, 7].
- arXiv:2003.08836 [pdf, other]
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Title: Topological Friction in a Kitaev Chain Heat EngineComments: 14 pages. arXiv admin note: substantial text overlap with arXiv:1908.02643Subjects: Statistical Mechanics (cond-mat.stat-mech)
We investigate a heat engine with a finite-length Kitaev chain in an ideal Otto cycle. It is found that the critical point of the topological phase transition coincides with the maxima of the efficiency and work output of the total Otto engine. Finite size effects are taken into account using the method of Hill's nanothermodynamics, as well as using the method of temperature-dependent energy levels. We identify the bulk and boundary thermal cycles of the Kitaev chain engine and find that they are non-ideal Otto cycles. The physics of deviation from ideal Otto cycle is identified as a finite size effect, which we dub as "topological friction", leading to heat transfer from the bulk to the boundary during adiabatic transformation of the whole system. Besides, we have determined the regimes allowing for independently running an ideal Otto refrigerator at the boundary and ideal Otto engines in the bulk and in the whole system. Furthermore, we show that the first-order phase transition in the boundary and the second-order phase transition in the bulk can be identified through their respective contributions to the engine work output.
- arXiv:2003.08838 [pdf, other]
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Title: Superconducting quantum many-body circuits for quantum simulation and computingComments: 8 pages, 4 figures, invited APL Perspectives paperJournal-ref: Appl. Phys. Lett. 116, 230501 (2020)Subjects: Quantum Physics (quant-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Quantum simulators are attractive as a means to study many-body quantum systems that are not amenable to classical numerical treatment. A versatile framework for quantum simulation is offered by superconducting circuits. In this perspective, we discuss how superconducting circuits allow the engineering of a wide variety of interactions, which in turn allows the simulation of a wide variety of model Hamiltonians. In particular we focus on strong photon-photon interactions mediated by nonlinear elements. This includes on-site, nearest-neighbour and four-body interactions in lattice models, allowing the implementation of extended Bose-Hubbard models and the toric code. We discuss not only the present state in analogue quantum simulation, but also future perspectives of superconducting quantum simulation that open up when concatenating quantum gates in emerging quantum computing platforms.
- arXiv:2003.08864 [pdf, other]
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Title: Interaction induced dynamical $\mathcal{PT}$ symmetry breaking in dissipative Fermi-Hubbard modelsComments: 9 pages, 9 figuresSubjects: Quantum Gases (cond-mat.quant-gas)
We investigate the dynamical properties of one-dimensional dissipative Fermi-Hubbard models, which are described by the Lindblad master equations with site-dependent jump operators. The corresponding non-Hermitian effective Hamiltonians with pure loss terms possess parity-time ($\mathcal{PT}$) symmetry after compensating an overall gain term. By solving the two-site Lindblad equation with fixed dissipation exactly, we find that the dynamics of rescaled density matrix shows an instability as the interaction increases over a threshold, which can be equivalently described in the scheme of non-Hermitian effective Hamiltonians. This instability is also observed in multi-site systems and closely related to the $\mathcal{PT}$ symmetry breaking accompanied by appearance of complex eigenvalues of the effective Hamiltonian. Moreover, we unveil that the dynamical instability of the anti-ferromagnetic Mott phase comes from the $\mathcal{PT}$ symmetry breaking in highly excited bands, although the low-energy effective model of the non-Hermitian Hubbard model in the strongly interacting regime is always Hermitian. We also provide a quantitative estimation of the time for the observation of dynamical $\mathcal{PT}$ symmetry breaking which could be probed in experiments.
- arXiv:2003.08868 [pdf]
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Title: Ostwald growth rate in controlled Covid-19 epidemic spreading as in arrested growth in quantum complex matterComments: 2 figures, 7 pagesJournal-ref: Condens. Matter 2020, 5, 23Subjects: Physics and Society (physics.soc-ph); Other Condensed Matter (cond-mat.other); Populations and Evolution (q-bio.PE)
Here, we focus on the data analysis of the growth of epidemic spread of Covid-19 in countries where different policies of containment were activated. It is known that the growth of pandemic spread at its threshold is exponential, but it is not known how to quantify the success of different containment policies. We identify that a successful approach gives an arrested phase regime following the Ostwald growth, where, over the course of time, one phase transforms into another metastable phase with a similar free energy as observed in oxygen interstitial diffusion in quantum complex matter and in crystallization of proteins. We introduce the s factor which provides a quantitative measure of the efficiency and speed of the adopted containment policy, which is very helpful not only to monitor the Covid-19 pandemic spread but also for other countries to choose the best containment policy. The results show that a policy based on joint confinement, targeted tests, and tracking positive cases is the most rapid pandemic containment policy; in fact, we found values of 9, 5, and 31 for the success s factor for China, South Korea, and Italy, respectively, where the lowest s factor indicates the best containment policy
- arXiv:2003.08869 [pdf, other]
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Title: Sensitive capacitive pressure sensors based on graphene membrane arraysAuthors: Makars Šiškins, Martin Lee, Dominique Wehenkel, Richard van Rijn, Tijmen W. de Jong, Johannes R. Renshof, Berend C. Hopman, Willemijn S. J. M. Peters, Dejan Davidovikj, Herre S. J. van der Zant, Peter G. SteenekenSubjects: Applied Physics (physics.app-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Other Condensed Matter (cond-mat.other)
The high flexibility, impermeability and strength of graphene membranes are key properties that can enable the next generation of nanomechanical sensors. However, for capacitive pressure sensors the sensitivity offered by a single suspended graphene membrane is too small to compete with commercial sensors. Here, we realize highly sensitive capacitive pressure sensors consisting of arrays of nearly ten thousand small, freestanding double-layer graphene membranes. We fabricate large arrays of small diameter membranes using a procedure that maintains the superior material and mechanical properties of graphene, even after high-temperature anneals. These sensors are readout using a low cost battery-powered circuit board, with a responsivity of up to 47.8 aF Pa$^{-1}$ mm$^{-2}$, thereby outperforming commercial sensors.
- arXiv:2003.08879 [pdf, other]
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Title: Revisiting the Common Neighbour Analysis and the Centrosymmetry ParameterAuthors: Peter M LarsenComments: 11 pages, 8 figuresSubjects: Computational Physics (physics.comp-ph); Materials Science (cond-mat.mtrl-sci)
We review two standard methods for structural classification in simulations of crystalline phases, the Common Neighbour Analysis and the Centrosymmetry Parameter. We explore the definitions and implementations of each of their common variants, and investigate their respective failure modes and classification biases. Simple modifications to both methods are proposed, which improve their robustness, interpretability, and applicability. We denote these variants the Interval Common Neighbour Analysis, and the Minimum-Weight Matching Centrosymmetry Parameter.
- arXiv:2003.08886 [pdf]
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Title: Native point defects and low $p$-doping efficiency in $Mg_2 (Si,Sn)$ solid solutions: A hybrid-density functional studyAuthors: Byungki Ryu, Eun-Ae Choi, Sungjin Park, Jaywan Chung, Johannes de Boor, Pawel Ziolkowski, Eckhard Müller, SuDong ParkComments: Main: 17 pages (including title, abstract, main, references, figure captions. 4 figures). Additional 11 pages for Supporting InformationSubjects: Materials Science (cond-mat.mtrl-sci)
We perform hybrid-density functional calculations to investigate the charged defect formation energy of native point defects in $Mg_2 Si$, $Mg_2 Sn$, and their solid solutions. The band gap correction by hybrid-density functional is found to be critical to determine the charged defect density in these materials. For $Mg_2 Si$, $Mg$ interstitials are dominant and provide unintentional $n$-type conductivity. Additionally, as the $Mg$ vacancies can dominate in $Mg$-poor $Mg_2 Sn$, $p$-type conductivity is possible for $Mg_2 Sn$. However, the existence of low formation energy defects such as $Mg_{Sn}^{1+}$ and $I_{Mg}^{2+}$ in $Mg_2 Sn$ and their diffusion can cause severe charge compensation of hole carriers resulting in low $p$-type doping efficiency and thermal degradation. Our results indicate that, in addition to the extrinsic doping strategy, alloying of $Mg_2 Si$ with $Mg_2 Sn$ under $Mg$-poor conditions would be necessary to enhance the $p$-type conductivity with less charge compensation.
- arXiv:2003.08887 [pdf]
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Title: Dependence of nonthermal metallization kinetics on bond ionicity of compoundsSubjects: Materials Science (cond-mat.mtrl-sci)
It is known that covalently bonded materials undergo nonthermal structure transformations upon ultrafast excitation of an electronic system, whereas metals exhibit phonon hardening. Here we study how ionic bonds react to electronic excitation. Density-functional molecular dynamics predicts that ionic crystals may melt nonthermally, however, into an electronically insulating state, in contrast to covalent materials. We demonstrate that the band gap behavior during nonthermal transitions depends on a bonding type: it is harder to collapse the band gap in more ionic compounds, which is illustrated by transformations in Y2O3 vs. NaCl, LiF and KBr.
- arXiv:2003.08889 [pdf, other]
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Title: Infinite-pressure phase diagram of binary mixtures of (non)additive hard disksSubjects: Soft Condensed Matter (cond-mat.soft)
One versatile route to the creation of two-dimensional crystal structures on the nanometer to micrometer scale is the self-assembly of colloidal particles at an interface. Here, we explore the crystal phases that can be expected from the self-assembly of mixtures of spherical particles of two different sizes, which we map to (additive or non-additive) hard-disk mixtures. We map out the infinite-pressure phase diagram for these mixtures, using Floppy Box Monte Carlo simulations to systematically sample candidate crystal structures with up to 12 disks in the unit cell. As a function of the size ratio and number ratio of the two species of particles, we find a rich variety of periodic crystal structures. Additionally, we identify random tiling regions to predict random tiling quasicrystal stability ranges. Increasing non-additivity both gives rise to additional crystal phases and broadens the stability regime for crystal structures involving a large number of large-small contacts, including random tilings. Our results provide useful guidelines for controlling the self-assembly of colloidal particles at interfaces.
- arXiv:2003.08893 [pdf, other]
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Title: Phonon-Phonon Interactions in Strongly Bonded Solids: Selection Rules and Higher-Order ProcessesComments: 18 pages, 7 figuresSubjects: Materials Science (cond-mat.mtrl-sci)
We show that the commonly used lowest-order theory of phonon-phonon interactions frequently fails to accurately describe the anharmonic phonon decay rates and thermal conductivity ($\kappa$), even among strongly bonded crystals. Applying a first principles theory that includes both the lowest-order three-phonon and the higher-order four-phonon processes to seventeen zinc blende semiconductors, we find that the lowest-order theory drastically overestimates the measured $\kappa$ for many of these materials, while inclusion of four-phonon scattering gives significantly improved agreement with measurements. We have identified new selection rules on three-phonon processes that help explain many of these failures in terms of anomalously weak anharmonic phonon decay rates predicted by the lowest-order theory competing with four-phonon processes. We also show that zinc blende compounds containing boron (B), carbon (C) or nitrogen (N) atoms have exceptionally weak four-phonon scattering, much weaker than in compounds that do not contain B, C or N atoms. This new understanding helps explain the ultrahigh $\kappa$ in several technologically important materials like cubic boron arsenide, boron phosphide and silicon carbide. At the same time, it not only makes the possibility of achieving high $\kappa$ in materials without B, C or N atoms unlikely, but it also suggests that it may be necessary to include four-phonon processes in many future studies. Our work gives new insights into the nature of anharmonic processes in solids and demonstrates the broad importance of higher-order phonon-phonon interactions in assessing the thermal properties of materials.
- arXiv:2003.08918 [pdf, ps, other]
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Title: Delay time of waves performing Lévy flights in 1D random mediaAuthors: L. A. Razo-López (1), A. A. Fernández-Marín (1), J. A. Méndez-Bermúdez (1), J. Sánchez-Dehesa (2), V. A. Gopar (3) ((1) Instituto de Física, Benemérita Universidad Autónoma de Puebla, (2) Departamento de Ingeniería Electrónica, Universitat Politècnica de València, (3) Departamento de Física Teórica, Facultad de Ciencias, and BIFI, Universidad de Zaragoza)Comments: 6 pages, 5 figuresSubjects: Disordered Systems and Neural Networks (cond-mat.dis-nn); Statistical Mechanics (cond-mat.stat-mech); Optics (physics.optics)
The time that waves spend inside 1D random media with the possibility of performing L\'evy flights is experimentally and theoretically studied. The dynamics of quantum and classical wave diffusion has been investigated in canonical disordered systems via the delay time. We show that a wide class of disorder--L\'evy disorder--leads to strong random fluctuations of the delay time; nevertheless, the tail of the distribution and the average of the delay time are insensitive to L\'evy flights. Our results reveal a universal character of wave propagation that goes beyond standard Brownian wave-diffusion.
- arXiv:2003.08930 [pdf, ps, other]
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Title: Validation of secondary fluorescence excitation in quantitative X-ray fluorescence analysis of thin alloy filmsSubjects: Materials Science (cond-mat.mtrl-sci); Applied Physics (physics.app-ph); Chemical Physics (physics.chem-ph)
X-ray fluorescence (XRF) analysis is a widely applied technique for the quantitative analysis of thin films up to the $\mu$m scale because of its non-destructive nature and because it is easily automated. When low uncertainties of the analytical results in the few percent range are required, the non-linear secondary fluorescence effect in multi-elemental samples may complicate an otherwise straightforward quantification, since it can easily exceed a relative contribution of 20%. The conventional solution, to rely on good performing reference samples, is hindered by their low availability, especially for thin film applications. To address this challenge, we demonstrate a flexible production method of multilayered, alloyed thin films with significant secondary fluorescence contributions. We use reference-free XRF analysis to validate the reliability of the physical model for secondary fluorescence, which includes a thorough uncertainty estimation. The investigated specimens are being qualified as calibration samples for XRF or other quantitative analyses.
- arXiv:2003.08931 [pdf, ps, other]
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Title: Integrable Lattice Models and HolographyAuthors: Meer AshwinkumarComments: Additional discussion and minor improvements, 20 pages, 8 figuresSubjects: High Energy Physics - Theory (hep-th); Statistical Mechanics (cond-mat.stat-mech); Mathematical Physics (math-ph)
We study four-dimensional Chern-Simons theory on $D \times \mathbb{C}$ (where $D$ is a disk), which is understood to describe rational solutions of the Yang-Baxter equation from the work of Costello, Witten and Yamazaki. We find that the theory is dual to a boundary theory, that is a three-dimensional analogue of the two-dimensional chiral WZW model. This boundary theory gives rise to a current algebra that turns out to be an "analytically-continued" toroidal Lie algebra. In addition, we show how certain bulk correlation functions of two and three Wilson lines can be captured by boundary correlation functions of local operators in the three-dimensional WZW model. In particular, we reproduce the leading and subleading nontrivial contributions to the rational R-matrix purely from the boundary theory.
Replacements
- arXiv:1711.04302 (replaced) [pdf, ps, other]
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Title: Lattice vibrations in the harmonic approximationSubjects: Materials Science (cond-mat.mtrl-sci); Strongly Correlated Electrons (cond-mat.str-el); Mathematical Physics (math-ph); Quantum Physics (quant-ph)
We present some theoretical results on the lattice vibrations that are necessary for a concise derivation of the Debye-Waller factor in the harmonic approximation. First we obtain an expression for displacement of an atom in a crystal lattice from its equilibrium position. Then we show that an atomic displacement has the Gaussian distribution. Finally, we obtain the computational formula for the Debye-Waller factor in the Debye model.
- arXiv:1808.07362 (replaced) [pdf, other]
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Title: Energy current manipulation and reversal of rectification in graded XXZ spin chainsJournal-ref: J. Phys.: Condens. Matter 32 175403 (2020)Subjects: Statistical Mechanics (cond-mat.stat-mech); Quantum Physics (quant-ph)
This work is devoted to the investigation of nontrivial transport properties in many-body quantum systems. Precisely, we study transport in the steady state of spin-1/2 Heisenberg XXZ chains, driven out of equilibrium by two magnetic baths with fixed, different magnetization. We take graded versions of the model, i.e., asymmetric chains in which some structure gradually changes in space. We investigate how we can manipulate and control the energy and spin currents of such chains by tuning external and/or inner parameters. In particular, we describe the occurrence of energy current rectification and its reversal due to the application of external magnetic fields. We show that, after carefully chosen the inner parameters of the system, by turning on an external magnetic field we can find spin and energy currents propagating in different directions. More interestingly, we may find cases in which rectifications of the energy and of the spin currents occur in opposite directions, i.e., if the energy current is larger when flowing from left to right side, then the spin current is larger if it flows from the right to left side. We still describe situations with inversion of the energy current direction as we increase the system asymmetry. We stress that our work aims the development of theoretical knowledge as well as the stimulation of future experimental applications.
- arXiv:1810.08222 (replaced) [pdf]
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Title: Visualization of multifractal superconductivity in a two-dimensional transition metal dichalcogenide in the weak-disorder regimeAuthors: Carmen Rubio-Verdú, Antonio M. García-García, Hyejin Ryu, Deung-Jang Choi, Javier Zaldívar, Shujie Tang, Bo Fan, Zhi-Xun Shen, Sung-Kwan Mo, José Ignacio Pascual, Miguel M. UgedaSubjects: Superconductivity (cond-mat.supr-con)
Eigenstate multifractality is a distinctive feature of non-interacting disordered metals close to a metal-insulator transition, whose properties are expected to extend to superconductivity. While multifractality in three dimensions (3D) only develops near the critical point for specific strong-disorder strengths, multifractality in 2D systems is expected to be observable even for weak disorder. Here we provide evidence for multifractal features in the superconducting state of an intrinsic weakly disordered single-layer NbSe$_2$ by means of low-temperature scanning tunneling microscopy/spectroscopy. The superconducting gap, characterized by its width, depth and coherence peaks' amplitude, shows a characteristic spatial modulation coincident with the periodicity of the quasiparticle interference pattern. Spatial inhomogeneity of the superconducting gap width, proportional to the local order parameter in the weak-disorder regime, follows a log-normal statistical distribution as well as a power-law decay of the two-point correlation function, in agreement with our theoretical model. Furthermore, the experimental singularity spectrum f($\alpha$) shows anomalous scaling behavior typical from 2D weakly disordered systems.
- arXiv:1903.09652 (replaced) [pdf, other]
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Title: Quench, thermalization and residual entropy across a non-Fermi liquid to Fermi liquid transitionComments: 5 pages, 3 figures, and supplementary materialJournal-ref: Phys. Rev. Research 2, 013307 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el); High Energy Physics - Theory (hep-th)
We study the thermalization, after sudden and slow quenches, of an interacting model having a quantum phase transition from a Sachdev-Ye-Kitaev (SYK) non-Fermi liquid (NFL) to a Fermi liquid (FL). The model has SYK fermions coupled to non-interacting lead fermions and can be realized in a graphene flake connected to external leads. After a sudden quench to the NFL, a thermal state is reached rapidly via collapse-revival oscillations of the quasiparticle residue of the lead fermions. In contrast, the quench to the FL, across the NFL-FL transition, leads to multiple prethermal regimes and much slower thermalization. In the slow quench performed over a time $\tau$, we find that the excitation energy generated has a remarkable intermediate-$\tau$ non-analytic power-law dependence, $\tau^{-\eta}$ with $\eta<1$, which seemingly masks the dynamical manifestation of the initial residual entropy of the SYK fermions. The power-law scaling is expected to eventually break down for $\tau\to\infty$, signaling a violation of adiabaticity, due to the residual entropy present in the SYK fermions.
- arXiv:1904.05918 (replaced) [pdf, other]
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Title: Entanglement entropy from nonequilibrium workAuthors: Jonathan D'EmidioComments: Published version. Added T=0 projector QMC simulations on lattice sizes up to 192 x 96Journal-ref: Phys. Rev. Lett. 124, 110602 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el); Statistical Mechanics (cond-mat.stat-mech)
The R\'enyi entanglement entropy in quantum many-body systems can be viewed as the difference in free energy between partition functions with different trace topologies. We introduce an external field $\lambda$ that controls the partition function topology, allowing us to define a notion of nonequilibrium work as $\lambda$ is varied smoothly. Nonequilibrium fluctuation theorems of the work provide us with statistically exact estimates of the R\'enyi entanglement entropy. This framework also naturally leads to the idea of using quench functions with spatially smooth profiles, providing us a way to average over lattice scale features of the entanglement entropy while preserving long distance universal information. We use these ideas to extract universal information from quantum Monte Carlo simulations of SU(N) spin models in one and two dimensions. The vast gain in efficiency of this method allows us to access unprecedented system sizes up to 192 x 96 spins for the square lattice Heisenberg antiferromagnet.
- arXiv:1905.09092 (replaced) [pdf, other]
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Title: Time-Delay PolaritonicsJournal-ref: Communications Physics 3, 2 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Non-linearity and finite signal propagation speeds are omnipresent in nature, technologies, and real-world problems, where efficient ways of describing and predicting the effects of these elements are in high demand. Advances in engineering condensed matter systems, such as lattices of trapped condensates, have enabled studies on non-linear effects in many-body systems where exchange of particles between lattice nodes is effectively instantaneous. Here, we demonstrate a regime of macroscopic matter-wave systems, in which ballistically expanding condensates of microcavity exciton-polaritons act as picosecond, microscale non-linear oscillators subject to time-delayed interaction. The ease of optical control and readout of polariton condensates enables us to explore the phase space of two interacting condensates up to macroscopic distances highlighting its potential in extended configurations. We demonstrate deterministic tuning of the coupled-condensate system between fixed point and limit cycle regimes, which is fully reproduced by time-delayed coupled equations of motion similar to the Lang-Kobayashi equation.
- arXiv:1906.02464 (replaced) [pdf]
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Title: Topological Ring-Cavity Laser Formed by Honeycomb Photonic CrystalsSubjects: Optics (physics.optics); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci)
We clarify theoretically that the topological ring-cavity (TRC) modes propagating along the interface between two honeycomb-type photonic crystals distinct in topology can be exploited for achieving stable single-mode lasing, with the maximal intensity larger than a whispering-gallery-mode counterpart by order of magnitude. Especially, we show that the TRC modes located at the bulk bandgap center benefit maximally from the gain profile since they are most concentrated and uniform along the ring cavity, and that, inheriting from the Dirac-like dispersion of topological interface states, they are separated in frequency from each other and from other photonic modes, both favoring intrinsically single-mode lasing. A TRC mode running in a specific direction with desired orbital angular momentum can be stimulated selectively by injecting circularly polarized light. The TRC laser proposed in the present work can be fabricated by means of advanced semiconductor nanotechnologies, which generates chiral laser beams ideal for novel photonic functions.
- arXiv:1906.11280 (replaced) [pdf, other]
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Title: Time evolution of correlation functions in quantum many-body systemsComments: 7+11 pages, 5 figures, comments welcome. v3 matches published versionJournal-ref: Phys. Rev. Lett. 124, 110605 (2020)Subjects: Quantum Physics (quant-ph); Statistical Mechanics (cond-mat.stat-mech); Strongly Correlated Electrons (cond-mat.str-el)
We give rigorous analytical results on the temporal behavior of two-point correlation functions --also known as dynamical response functions or Green's functions-- in closed many-body quantum systems. We show that in a large class of translation-invariant models the correlation functions factorize at late times $\langle A(t) B\rangle_\beta \rightarrow \langle A \rangle_\beta \langle B \rangle_\beta$, thus proving that dissipation emerges out of the unitary dynamics of the system. We also show that for systems with a generic spectrum the fluctuations around this late-time value are bounded by the purity of the thermal ensemble, which generally decays exponentially with system size. For auto-correlation functions we provide an upper bound on the timescale at which they reach the factorized late time value. Remarkably, this bound is only a function of local expectation values, and does not increase with system size. We give numerical examples that show that this bound is a good estimate in non-integrable models, and argue that the timescale that appears can be understood in terms of an emergent fluctuation-dissipation theorem. Our study extends to further classes of two point functions such as the symmetrized ones and the Kubo function that appears in linear response theory, for which we give analogous results.
- arXiv:1907.07155 (replaced) [pdf, other]
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Title: Direct Calculation of Mutual Information of Distant RegionsAuthors: Noburo ShibaComments: 17 pages; v2, added references, minor corrections in eq.(3.20). arXiv admin note: text overlap with arXiv:1408.0637Subjects: High Energy Physics - Theory (hep-th); Strongly Correlated Electrons (cond-mat.str-el); Quantum Physics (quant-ph)
We consider the (Renyi) mutual information, $I^{(n)}(A,B) = S^{(n)}_A+S^{(n)}_{B} - S^{(n)}_{A \cup B}$, of distant compact spatial regions A and B in the vacuum state of a free scalar field. The distance r between A and B is much greater than their sizes $R_{A,B}$. It is known that $I^{(n)}(A,B) \sim C^{(n)}_{AB} \left<0| \phi(r)\phi(0) |0\right>^2$ . We obtain the direct expression of $C^{(n)}_{AB}$ for arbitrary regions A and B. We perform the analytical continuation of $n$ and obtain the mutual information. The direct expression is useful for the numerical computation. By using the direct expression, we can compute directly $I(A,B)$ without computing $S_A, S_B$ and $S_{A \cup B}$ respectively, so it reduces significantly the amount of computation.
- arXiv:1908.06110 (replaced) [pdf, other]
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Title: Antiferromagnetic cavity optomagnonicsComments: 11 pages, 5 figuresJournal-ref: Phys. Rev. Research 2, 022027 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Quantum Physics (quant-ph)
Currently, there is a growing interest in studying the coherent interaction between magnetic systems and electromagnetic radiation in a cavity, prompted partly by possible applications in hybrid quantum systems. We propose a multimode cavity optomagnonic system based on antiferromagnetic insulators, where optical photons couple coherently to the two homogeneous magnon modes of the antiferromagnet. These have frequencies typically in the THz range, a regime so far mostly unexplored in the realm of coherent interactions, and which makes antiferromagnets attractive for quantum transduction from THz to optical frequencies. We derive the theoretical model for the coupled system, and show that it presents unique characteristics. In particular, if the antiferromagnet presents hard-axis magnetic anisotropy, the optomagnonic coupling can be tuned by a magnetic field applied along the easy axis. This allows to bring a selected magnon mode into and out of a dark mode, providing an alternative for a quantum memory protocol. The dynamical features of the driven system present unusual behavior due to optically induced magnon-magnon interactions, including regions of magnon heating for a red detuned driving laser. The multimode character of the system is evident in a substructure of the optomagnonically induced transparency window.
- arXiv:1908.10597 (replaced) [pdf, other]
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Title: Fluctuation Relations For Adiabatic PumpingSubjects: Statistical Mechanics (cond-mat.stat-mech)
We derive an extended fluctuation relation for an open system coupled with two reservoirs under adiabatic one-cycle modulation. We confirm that the geometric phase caused by the Berry-Sintisyn-Nemenman curvature in the parameter space generates non-Gaussian fluctuations. This non-Gaussianity is enhanced for the instantaneous fluctuation relation when the bias between the two reservoirs disappears.
- arXiv:1908.11718 (replaced) [pdf, other]
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Title: Giant Orbital Magneto-electric effect and Current-driven Magnetization Switching in Twisted Bilayer GrapheneComments: 9 pages, 4 figures, plus supplementary material. To appear in Nature CommunicationsJournal-ref: Nature Communications 11, 1650 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Recently, signatures of quantum anomalous Hall states with spontaneous ferromagnetism were observed in twisted bilayer graphenes (TBGs) near 3/4 filling [1, 2]. Importantly, it was demon-strated that an extremely small current can switch the direction of the magnetization. This offers the prospect of realizing low energy dissipation magnetic memories. However, the mechanism of the current-driven magnetization switching is poorly understood as the charge currents in graphene layers are generally believed to be non-magnetic. In this work, we demonstrate that, in TBGs, the twist-induced reduction of lattice symmetry allows a charge current to generate net orbital magnetization at a general filling factor through magnetoelectric effects. Substrate-induced strain and sublattice symmetry breaking further reduce the symmetry such that an out-of-plane orbital magnetization can be generated. Due to the large non-trivial Berry phase of the flat bands, the orbital magnetization of a Bloch state can be as large as tens of Bohr magnetons and therefore a small current would be sufficient to generate a large orbital magnetization. We further demonstrate how the charge current with orbital magnetization can switch the magnetization of the quantum anomalous Hall state near 3/4 filling as observed in the experiments [1, 2].
- arXiv:1909.09573 (replaced) [pdf, other]
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Title: Dimer Physics in the Frustrated Cairo Pentagonal Antiferromagnet Bi2Fe4O9Authors: K. Beauvois, V. Simonet, S. Petit, J. Robert, F. Bourdarot, M. Gospodinov, A. A. Mukhin, R. Ballou, V. Skumryev, E. RessoucheComments: Article: 6 pages, 3 figures. Supplemental Material: 10 pages, 10 figuresJournal-ref: Phys. Rev. Lett. 124, 127202 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el)
The research field of magnetic frustration is dominated by triangle-based lattices but exotic phenomena can also be observed in pentagonal networks. A peculiar noncollinear magnetic order is indeed known to be stabilized in Bi2Fe4O9 materializing a Cairo pentagonal lattice. We present the spin wave excitations in the magnetically ordered state, obtained by inelastic neutron scattering. They reveal an unconventional excited state related to local precession of pairs of spins. The magnetic excitations are then modeled to determine the superexchange interactions for which the frustration is indeed at the origin of the spin arrangement. This analysis unveils a hierarchy in the interactions, leading to a paramagnetic state (close to the N\'eel temperature) constituted of strongly coupled dimers separated by much less correlated spins. This produces two types of response to an applied magnetic field associated with the two nonequivalent Fe sites, as observed in the magnetization distributions obtained using polarized neutrons.
- arXiv:1910.00196 (replaced) [pdf, other]
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Title: Unique Dirac and Triple point fermiology in simple transition metals and their binary alloysAuthors: Chiranjit Mondal, Chanchal K. Barman, Shuvam Sarkar, Sudipta Roy Barman, Aftab Alam, Biswarup PathakJournal-ref: Phys. Rev. B 101, 155108 (2020)Subjects: Materials Science (cond-mat.mtrl-sci); Strongly Correlated Electrons (cond-mat.str-el)
Noble metal surfaces (Au, Ag and Cu etc.) have been extensively studied for the Shockley type surface states (SSs). Very recently, some of these Shockley SSs have been understood from the topological consideration, with the knowledge of global properties of electronic structure. In this letter, we show the existence of Dirac like excitations in the elemental noble metal Ru, Re and Os based on symmetry analysis and first principle calculations. The unique SSs driven Fermi arcs have been investigated in details for these metals. Our calculated SSs and Fermi arcs are consistent with the previous transport and photo-emission results. We attribute these Dirac excitation mediated Fermi arc topology to be the possible reasons behind several existing transport anomalies, such as large non-saturating magneto resistance, anomalous Nernst electromotive force and its giant oscillations, magnetic breakdown etc. We further show that the Dirac like excitations in these elemental metal can further be tuned to three component Fermionic excitations, using symmetry allowed alloy mechanism.
- arXiv:1910.09918 (replaced) [pdf, other]
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Title: From complex to simple : hierarchical free-energy landscape renormalized in deep neural networksAuthors: Hajime YoshinoComments: 61 pages, 20 figures, revised version, to appear in SciPost Phys CoreJournal-ref: SciPost Phys. Core 2, 005 (2020)Subjects: Disordered Systems and Neural Networks (cond-mat.dis-nn); Statistical Mechanics (cond-mat.stat-mech); Machine Learning (cs.LG); Machine Learning (stat.ML)
We develop a statistical mechanical approach based on the replica method to study the design space of deep and wide neural networks constrained to meet a large number of training data. Specifically, we analyze the configuration space of the synaptic weights and neurons in the hidden layers in a simple feed-forward perceptron network for two scenarios: a setting with random inputs/outputs and a teacher-student setting. By increasing the strength of constraints,~i.e. increasing the number of training data, successive 2nd order glass transition (random inputs/outputs) or 2nd order crystalline transition (teacher-student setting) take place layer-by-layer starting next to the inputs/outputs boundaries going deeper into the bulk with the thickness of the solid phase growing logarithmically with the data size. This implies the typical storage capacity of the network grows exponentially fast with the depth. In a deep enough network, the central part remains in the liquid phase. We argue that in systems of finite width N, the weak bias field can remain in the center and plays the role of a symmetry-breaking field that connects the opposite sides of the system. The successive glass transitions bring about a hierarchical free-energy landscape with ultrametricity, which evolves in space: it is most complex close to the boundaries but becomes renormalized into progressively simpler ones in deeper layers. These observations provide clues to understand why deep neural networks operate efficiently. Finally, we present some numerical simulations of learning which reveal spatially heterogeneous glassy dynamics truncated by a finite width $N$ effect.
- arXiv:1910.10084 (replaced) [pdf, other]
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Title: Field-dependent ionic conductivities from generalized fluctuation-dissipation relationsComments: 6 pages, 3 figuresJournal-ref: Phys. Rev. Lett. 124, 206001 (2020)Subjects: Statistical Mechanics (cond-mat.stat-mech)
We derive a relationship for the electric field dependent ionic conductivity in terms of fluctuations of time integrated microscopic variables. We demonstrate this formalism with molecular dynamics simulations of solutions of differing ionic strength with implicit solvent conditions and molten salts. These calculations are aided by a novel nonequilibrium statistical reweighting scheme that allows for the conductivity to be computed as a continuous function of the applied field. In strong electrolytes, we find the fluctuations of the ionic current are Gaussian and subsequently the conductivity is constant with applied field. In weaker electrolytes and molten salts, we find the fluctuations of the ionic current are strongly non-Gaussian and the conductivity increases with applied field. This nonlinear behavior, known phenomenologically for dilute electrolytes as the Onsager-Wien effect, is general and results from the suppression of ionic correlations at large applied fields, as we elucidate through both dynamic and static correlations within nonequilibrium steady-states.
- arXiv:1910.10978 (replaced) [pdf, other]
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Title: Formulas for Partial Entanglement EntropyAuthors: Qiang WenComments: v3:21pages,version improved a lot; v4:typos corrected, matching with the published version on PRResearchJournal-ref: Phys. Rev. Research 2, 023170 (2020)Subjects: High Energy Physics - Theory (hep-th); Statistical Mechanics (cond-mat.stat-mech); General Relativity and Quantum Cosmology (gr-qc); Quantum Physics (quant-ph)
The partial entanglement entropy (PEE) $s_{\mathcal{A}}(\mathcal{A}_i)$ characterizes how much the subset $\mathcal{A}_i$ of $\mathcal{A}$ contribute to the entanglement entropy $S_{\mathcal{A}}$. We find one additional physical requirement for $s_{\mathcal{A}}(\mathcal{A}_i)$, which is the invariance under a permutation. The partial entanglement entropy proposal satisfies all the physical requirements. We show that for Poincar\'e invariant theories the physical requirements are enough to uniquely determine the PEE (or the entanglement contour) to satisfy a general formula. This is the first time we find the PEE can be uniquely determined. Since the solution of the requirements is unique and the \textit{PEE proposal} is a solution, the \textit{PEE proposal} is justified for Poincar\'e invariant theories.
- arXiv:1910.11526 (replaced) [pdf, other]
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Title: Orbital optimized unitary coupled cluster theory for quantum computerAuthors: Wataru Mizukami, Kosuke Mitarai, Yuya O. Nakagawa, Takahiro Yamamoto, Tennin Yan, Yu-ya OhnishiSubjects: Strongly Correlated Electrons (cond-mat.str-el); Quantum Physics (quant-ph)
We propose an orbital optimized method for unitary coupled cluster theory (OO-UCC) within the variational quantum eigensolver (VQE) framework for quantum computers. OO-UCC variationally determines the coupled cluster amplitudes and also molecular orbital coefficients. Owing to its fully variational nature, first-order properties are readily available. This feature allows the optimization of molecular structures in VQE without solving any additional equations. Furthermore, the method requires smaller active space and shallower quantum circuit than UCC to achieve the same accuracy. We present numerical examples of OO-UCC using quantum simulators, which include the geometry optimization of the water and ammonia molecules using analytical first derivatives of the VQE.
- arXiv:1910.12801 (replaced) [pdf, other]
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Title: Charge Density Wave and Superconductivity in Transition Metal DichalcogenidesJournal-ref: Eur. Phys. J. B 93, 77 (2020), EPJB special issueSubjects: Strongly Correlated Electrons (cond-mat.str-el)
Competing orders in condensed matter give rise to the emergence of fascinating, new phenomena. Here, we investigate the competition between superconductivity and charge density wave in the context of layered-metallic compounds, transition metal dichalcogenides, in which the superconducting state is usually suppressed by the charge density wave. We show, using real-space self-consistent Bogoliubov-de Gennes calculations and momentum-space calculations involving density-functional theory and dynamical mean-field theory, that there is a surprising reappearance of superconductivity in the presence of non-magnetic disorder fluctuations, as observed in recent experiments.
- arXiv:1911.00363 (replaced) [pdf, ps, other]
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Title: Doping effects on electronic states in electron-doped FeSe: Impact of self-energy and vertex correctionsComments: 9 pages, 8 figuresSubjects: Superconductivity (cond-mat.supr-con); Strongly Correlated Electrons (cond-mat.str-el)
The pairing glue of high-$T_{\rm c}$ superconductivity in heavily electron-doped (e-doped) FeSe, in which hole-pockets are absent, has been an important unsolved problem. Here, we focus on a heavily e-doped bulk superconductor Li$_{1-x}$Fe$_x$OHFeSe ($T_{\rm c} \sim 40$K). We construct a multiorbital model beyond the rigid band approximation and analyze the spin and orbital fluctuations by taking both vertex corrections (VCs) and self-energy into consideration. Without e-doping ($x=0$), the ferro-orbital order without magnetism in FeSe is reproduced by the VCs.The orbital order quickly disappears when the hole-pocket vanishes at $x \sim 0.03$. With increasing $x$ further, the spin fluctuations remain small, whereas orbital fluctuations gradually increase with $x$ due to the VCs. The negative feedback due to the self-energy is crucial to explain experimental phase diagram. Thanks to both vertex and self-energy corrections, the orbital-fluctuation-mediated $s_{++}$-wave state appears for a wide doping range, consistent with experiments.
- arXiv:1911.09455 (replaced) [pdf, ps, other]
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Title: Conductivity of a two-dimensional HgTe layer near the critical width: The role of developed edge states network and random mixture of $p$- and $n$-domainsComments: 9 pages, 7 figuresJournal-ref: Phys. Rev. B 101, 125415 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
The conductivity of a two-dimensional HgTe quantum well with a width $\sim$6.3~nm, close to the transition from ordinary to topological insulating phases, is studied. The Fermi level is supposed to get to the overall energy gap. The consideration is based on the percolation theory. We have found that the width fluctuations convert the system to a random mixture of domains with positive and negative energy gaps with internal edge states formed near zero gap lines. In the case with no potential fluctuations, the conductance of a finite sample is provided by a random edge states network. The zero-temperature conductivity of an infinite sample is determined by the free motion of electrons along the zero-gap lines and tunneling between them.
The conductance of a single $p$-$n$ junction, which is crossed by the edge state, is found. The result is applied to the situation when potential fluctuations transform the system to a mixture of $p$- and $n$-domains. It is stated that the tunneling across $p$-$n$ junctions forbids the low-temperature conductivity of a random system, but the latter is restored due to the random edge states crossing the junctions. - arXiv:1911.12853 (replaced) [pdf]
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Title: Determination of the trigonal warping orientation in Bernal-stacked bilayer graphene via scanning tunneling microscopyAuthors: Frédéric Joucken, Zhehao Ge, Eberth A. Quezada-López, John L. Davenport, Kenji Watanabe, Takashi Taniguchi, Jairo Velasco JrComments: Accepted in Phys. Rev. BJournal-ref: Phys. Rev. B 101, 161103 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci)
The existence of strong trigonal warping around the K point for the low energy electronic states in multilayer (N$\geq$2) graphene films and graphite is well established. It is responsible for phenomena such as Lifshitz transitions and anisotropic ballistic transport. The absolute orientation of the trigonal warping with respect to the center of the Brillouin zone is however not agreed upon. Here, we use quasiparticle scattering experiments on a gated bilayer graphene/hexagonal boron nitride heterostructure to settle this disagreement. We compare Fourier transforms of scattering interference maps acquired at various energies away from the charge neutrality point with tight-binding-based joint density of states simulations. This comparison enables unambiguous determination of the trigonal warping orientation for bilayer graphene low energy states. Our experimental technique is promising for quasi-directly studying fine features of the band structure of gated two-dimensional materials such as topological transitions, interlayer hybridization, and moir\'e minibands.
- arXiv:1912.03773 (replaced) [pdf]
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Title: Transport and thermodynamics in quantum junctions: A scattering approachComments: 86 pages, 2 figuresSubjects: Statistical Mechanics (cond-mat.stat-mech)
We present a scattering approach for the study of the transport and thermodynamics of quantum systems strongly coupled to their thermal environment(s). This formalism recovers the standard non-equilibrium Green's function expressions for quantum transport and reproduces recently obtained results for the quantum thermodynamic of slowly driven systems. Using this approach, new results have been obtained. First, we derived of a general explicit expression for non-equilibrium steady state density matrix of a system compromised of multiple infinite baths coupled through a general interaction. Then, we obtained a general expression for the dissipated power for the driven non-interacting resonant level to first order in the driving speeds, where both the dot energy level and its couplings are changing, without invoking the wide band approximation. In addition, we also showed that the symmetric splitting of system bath interaction, employed for the case of a system coupled to one bath to determine the effective system Hamiltonian [Phys. Rev. B 93, 115318 (2016)] is valid for the multiple baths case as well. Finally, we demonstrated an equivalence of our method to the Landauer-Buttiker formalism and its extension to slowly driven systems developed by von Oppen and co-workers [Phys. Rev. Lett. 120, 107701 (2018)]. To demonstrate the use of this formalism we analyze the operation a device in which the dot is driven cyclically between two leads under strong coupling conditions. We also generalize the previously obtained expression for entropy production in such driven processes to the many-bath case.
- arXiv:1912.10650 (replaced) [pdf, other]
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Title: Weighted Ensemble Milestoning (WEM): A Combined Approach for Rare Event SimulationsSubjects: Statistical Mechanics (cond-mat.stat-mech); Computational Physics (physics.comp-ph)
To directly simulate rare events using atomistic molecular dynamics is a significant challenge in computational biophysics. Well-established enhanced-sampling techniques do exist to obtain the thermodynamic functions for such systems. But developing methods for obtaining the kinetics of long timescale processes from simulation at atomic detail is comparatively less developed an area. Milestoning and the weighted ensemble (WE) method are two different stratification strategies; both have shown promise for computing long timescales of complex biomolecular processes. Nevertheless, both require a significant investment of computational resources. We have combined WE and milestoning to calculate observables in orders of magnitude less CPU and wall-clock time. Our weighted ensemble milestoning method (WEM) uses WE simulation to converge the transition probability and first passage times between milestones, followed by the utilization of the theoretical framework of milestoning to extract thermodynamic and kinetic properties of the entire process. We tested our method for a simple one-dimensional double well potential, an eleven-dimensional potential energy surface with energy barrier, and on the biomolecular model system alanine dipeptide. We were able to recover the free energy profiles, time correlation functions, and mean first passage times for barrier crossing events at a significantly small computational cost. WEM promises to extend the applicability of molecular dynamics simulation to slow dynamics of large systems which are well beyond the scope of present day brute-force computations.
- arXiv:1912.10931 (replaced) [pdf, ps, other]
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Title: Majorana and parafermion corner states from two coupled sheets of bilayer grapheneJournal-ref: Phys. Rev. Research 2, 013330 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We consider a setup consisting of two coupled sheets of bilayer graphene in the regime of strong spin-orbit interaction, where electrostatic confinement is used to create an array of effective quantum wires. We show that for suitable interwire couplings the system supports a topological insulator phase exhibiting Kramers partners of gapless helical edge states, while the additional presence of a small in-plane magnetic field and weak proximity-induced superconductivity leads to the emergence of zero-energy Majorana corner states at all four corners of a rectangular sample, indicating the transition to a second-order topological superconducting phase. The presence of strong electron-electron interactions is shown to promote the above phases to their exotic fractional counterparts. In particular, we find that the system supports a fractional topological insulator phase exhibiting fractionally charged gapless edge states and a fractional second-order topological superconducting phase exhibiting zero-energy $\mathbb{Z}_{2m}$ parafermion corner states, where $m$ is an odd integer determined by the position of the chemical potential.
- arXiv:2001.00075 (replaced) [pdf, other]
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Title: Bound states in two-dimensional Fermi systems with quadratic band touchingAuthors: Flávio L. N. Santos (1 and 2), Mônica A. Caracanhas (3), M. C. O. Aguiar (1 and 2), Rodrigo G. Pereira (4) ((1) Departamento de Física, Universidade Federal de Minas Gerais, Belo Horizonte, Brazil, (2) Université Paris-Saclay, CNRS, Laboratoire de Physiques des Solides, 91405, Orsay, France (3) Instituto de Física de São Carlos, Universidade de São Paulo, São Carlos, Brazil (4) International Institute of Physics and Departamento de Física Teórica e Experimental, Universidade Federal do Rio Grande do Norte, Natal, Brazil)Comments: 9 pages, 8 figuresJournal-ref: Phys. Rev. B 101, 155120 (2020)Subjects: Quantum Gases (cond-mat.quant-gas); Strongly Correlated Electrons (cond-mat.str-el)
The formation of bound states between mobile impurity particles and fermionic atoms has been demonstrated in spin-polarized Fermi gases with attractive interspecies interaction. We investigate bound states of mobile impurities immersed in a two-dimensional system with a symmetry-protected quadratic band touching. In addition to the standard s-wave interaction, we consider an anisotropic dipolar exchange interaction that locally breaks point group symmetries. Using a weak-coupling renormalization group approach and a ladder approximation for the impurity-fermion propagator, we establish that the number of bound states can be controlled by varying the anisotropy of the exchange interaction. Our results show that the degeneracy and momentum dependence of the binding energies reflect some distinctive properties of the quadratic band touching.
- arXiv:2001.03404 (replaced) [pdf, ps, other]
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Title: Microscopic theory of OMAR based on kinetic equations for quantum spin correlationsAuthors: A.V. ShumilinJournal-ref: Phys. Rev. B 101, 134201 (2020)Subjects: Disordered Systems and Neural Networks (cond-mat.dis-nn); Strongly Correlated Electrons (cond-mat.str-el)
The correlation kinetic equation approach is developed that allows describing spin correlations in a material with hopping transport. The quantum nature of spin is taken into account. The approach is applied to the problem of the bipolaron mechanism of organic magnetoresistance (OMAR) in the limit of large Hubbard energy and small applied electric field. The spin relaxation that is important to magnetoresistance is considered to be due to hyperfine interaction with atomic nuclei. It is shown that the lineshape of magnetoresistance depends on short-range transport properties. Different model systems with identical hyperfine interaction but different statistics of electron hops lead to different lineshapes of magnetoresistance including the two empirical laws $H^2/(H^2 + H_0^2)$ and $H^2/(|H| + H_0)^2$ that are commonly used to fit experimental results.
- arXiv:2001.04157 (replaced) [pdf, other]
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Title: Conductance of quantum spin Hall edge states from first principles: the critical role of magnetic impurities and inter-edge scatteringComments: 12 pages, 7 figures + Supplemental MaterialJournal-ref: Phys. Rev. B 101, 155404 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
The outstanding transport properties expected at the edge of two-dimensional time-reversal invariant topological insulators have proven to be challenging to realize experimentally, and have so far only been demonstrated in very short devices. In search for an explanation to this puzzling observation, we here report a full first-principles calculation of topologically protected transport at the edge of novel quantum spin Hall insulators - specifically, Bismuth and Antimony halides - based on the non-equilibrium Green's functions formalism. Our calculations unravel two different scattering mechanisms that may affect two-dimensional topological insulators, namely time-reversal symmetry breaking at vacancy defects and inter-edge scattering mediated by multiple co-operating impurities, possibly non-magnetic. We discuss their drastic consequences for typical non-local transport measurements as well as strategies to mitigate their negative impact. Finally, we provide an instructive comparison of the transport properties of topologically protected edge states to those of the trivial edge states in MoS$_2$ ribbons. Although we focus on a few specific cases (in terms of materials and defect types) our results should be representative for the general case and thus have significance beyond the systems studied here.
- arXiv:2001.06493 (replaced) [pdf, other]
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Title: Renormalization to localization without a small parameterComments: 22 pages, 7 figures, 55 referencesJournal-ref: SciPost Phys. 8, 049 (2020)Subjects: Disordered Systems and Neural Networks (cond-mat.dis-nn); Quantum Gases (cond-mat.quant-gas); Quantum Physics (quant-ph)
We study the wave function localization properties in a d-dimensional model of randomly spaced particles with isotropic hopping potential depending solely on Euclidean interparticle distances. Due to the generality of this model usually called the Euclidean random matrix model, it arises naturally in various physical contexts such as studies of vibrational modes, artificial atomic systems, liquids and glasses, ultracold gases and photon localization phenomena. We generalize the known Burin-Levitov renormalization group approach, formulate universal conditions sufficient for localization in such models and inspect a striking equivalence of the wave function spatial decay between Euclidean random matrices and translation-invariant long-range lattice models with a diagonal disorder.
- arXiv:2002.02066 (replaced) [pdf, other]
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Title: Hagedorn Temperature in Large $N$ Majorana Quantum MechanicsComments: 27 pages, 8 figures, v3: minor improvements, references addedSubjects: High Energy Physics - Theory (hep-th); Strongly Correlated Electrons (cond-mat.str-el)
We discuss two types of quantum mechanical models that couple large numbers of Majorana fermions and have orthogonal symmetry groups. In models of vector type, only one of the symmetry groups has a large rank. The large $N$ limit is taken keeping $gN=\lambda$ fixed, where $g$ multiplies the quartic Hamiltonian. We introduce a simple model with $O(N)\times SO(4)$ symmetry, whose energies are expressed in terms of the quadratic Casimirs of the symmetry groups. This model may be deformed so that the symmetry is $O(N)\times O(2)^2$, and the Hamiltonian reduces to that studied in arXiv:1802.10263. We find analytic expressions for the large $N$ density of states and free energy. In both vector models, the large $N$ density of states varies approximately as $e^{-|E|/\lambda}$ for a wide range of energies. This gives rise to critical behavior as the temperature approaches the Hagedorn temperature $T_{\rm H} = \lambda$. In the formal large $N$ limit, the specific heat blows up as $(T_H- T)^{-2}$, which implies that $T_H$ is the limiting temperature. However, at any finite $N$, it is possible to reach arbitrarily large temperatures. Thus, the finite $N$ effects smooth out the Hagedorn transition. We also study models of matrix type, which have two $O(N)$ symmetry groups with large rank. An example is provided by the Majorana matrix model with $O(N)^2\times O(2)$ symmetry, which was studied in arXiv:1802.10263. In contrast with the vector models, the density of states is smooth and nearly Gaussian near the middle of the spectrum.
- arXiv:2002.10297 (replaced) [pdf]
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Title: Flexible Amorphous Superconducting Materials and Quantum Devices with Unexpected TunabilityComments: 25 pages, 14 figures, 3 tablesSubjects: Superconductivity (cond-mat.supr-con); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci); Quantum Physics (quant-ph)
In superconductivity, electrons exhibit unique macroscopic collective quantum behavior that is the key for many modern quantum technologies. This electron behavior stems vastly from coupling to a correlated motion of atoms in the material, as well as from synchronized directional movement that screens external magnetic fields perfectly. Hence, the inter-atomic distance and material geometry are expected to affect fundamental superconductive characteristics. These parameters are tunable with strain, but strain application is hindered by the rigidity of superconductors, which in turn increases at device-relevant temperatures. Here, we present flexible, foldable and transferable superconducting materials, and functional quantum nanostructures by depositing superconductive amorphous-alloy films on a flexible adhesive tape. Specifically, flexible superconducting films, nanowires and quantum interference devices (SQUIDs) were fabricated and characterized under variable magnetic-field, current, temperature and flexure conditions. The SQUID interference periodicity, which represents a single flux quantum, exhibits unexpected tunability with folding curvature. This tunability raises a need for a relook at the fundamentals of superconductivity, mainly with respect to effects of geometry, magnetic-field inhomogeneity and strain. Our work paves the way for novel magnetic devices and quantum-technology platforms with local tunability.
- arXiv:2002.12824 (replaced) [pdf, other]
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Title: Quantum circuits with classically simulable operator scramblingComments: 4 pages, double column. v2: minor changes including an expanded introduction of gate setSubjects: Quantum Physics (quant-ph); Statistical Mechanics (cond-mat.stat-mech); Strongly Correlated Electrons (cond-mat.str-el); High Energy Physics - Theory (hep-th); Chaotic Dynamics (nlin.CD)
We introduce a new family of quantum circuits for which the scrambling of a subspace of non-local operators is classically simulable. We call these circuits `super-Clifford circuits', since the Heisenberg time evolution of these operators corresponds to a Clifford evolution in operator space. By simulating the Clifford evolution in operator space we are able to simulate the time evolution of certain single Pauli strings into operators with an operator entanglement that grows linearly with the number of qubits. These circuits provide a new technique for studying scrambling in systems with a large number of qubits, and are an explicit counter example to the intuition that classical simulability implies the absence of scrambling.
- arXiv:2002.12925 (replaced) [pdf, other]
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Title: Predicting excited states from ground state wavefunction by supervised quantum machine learningComments: 20 pages, 6 figures, 1 tableSubjects: Quantum Physics (quant-ph); Strongly Correlated Electrons (cond-mat.str-el); Chemical Physics (physics.chem-ph)
Excited states of molecules lie in the heart of photochemistry and chemical reactions. The recent development in quantum computational chemistry leads to inventions of a variety of algorithms that calculate the excited states of molecules on near-term quantum computers, but they require more computational burdens than the algorithms for calculating the ground states. In this study, we propose a scheme of supervised quantum machine learning which predicts the excited-state properties of molecules only from their ground state wavefunction resulting in reducing the computational cost for calculating the excited states. Our model is comprised of a quantum reservoir and a classical machine learning unit which processes the measurement results of single-qubit Pauli operators with the output state from the reservoir. The quantum reservoir effectively transforms the single-qubit operators into complicated multi-qubit ones which contain essential information of the system, so that the classical machine learning unit may decode them appropriately. The number of runs for quantum computers is saved by training only the classical machine learning unit, and the whole model requires modest resources of quantum hardware that may be implemented in current experiments. We illustrate the predictive ability of our model by numerical simulations for small molecules with and without noise inevitable in near-term quantum computers. The results show that our scheme well reproduces the first and second excitation energies as well as the transition dipole moment between the ground states and excited states only from the ground state as an input. We expect our contribution will enhance the applications of quantum computers in the study of quantum chemistry and quantum materials.
- arXiv:2003.03902 (replaced) [pdf, ps, other]
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Title: The Schwartz-Soffer and more inequalities for random fieldsComments: 14 pagesSubjects: Mathematical Physics (math-ph); Disordered Systems and Neural Networks (cond-mat.dis-nn)
A new series of correlation inequalities for random field spin systems is proven rigorously. First one corresponds to the well-known Schwartz-Soffer inequality. These are expected to rule out incorrect results calculated in effective theories and numerical studies. The large $N$ expansion with the replica method for random field systems as an example is checked by these inequalities. It is shown that several critical exponents of multiple-point correlation functions at critical point satisfy obtained inequalities.
- arXiv:2003.04670 (replaced) [pdf, other]
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Title: Symmetry resolved entanglement entropy of excited states in a CFTSubjects: Statistical Mechanics (cond-mat.stat-mech)
We report a throughout analysis of the entanglement entropies related to different symmetry sectors in the low-lying primary excited states of a conformal field theory (CFT) with an internal U(1) symmetry. Our findings extend recent results for the ground state. We derive a general expression for the charged moments, i.e. the generalised cumulant generating function, which can be written in terms of correlation functions of the operator that define the state through the CFT operator-state correspondence. We provide explicit analytic computations for the compact boson CFT (aka Luttinger liquid) for the vertex and derivative excitations. The Fourier transform of the charged moments gives the desired symmetry resolved entropies. At the leading order, they satisfy entanglement equipartition, as in the ground state, but we find, within CFT, subleading terms that break it. Our analytical findings are checked against free fermions calculations on a lattice, finding excellent agreement. As a byproduct, we have exact results for the full counting statistics of the U(1) charge in the considered excited states.
- arXiv:2003.06229 (replaced) [pdf, other]
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Title: Microfluidic In Situ Measurement of Poisson's Ratio of HydrogelsJournal-ref: Micromachines 2020, 11(3), 318;Subjects: Soft Condensed Matter (cond-mat.soft)
Being able to precisely characterize the mechanical properties of soft microparticles is essential for numerous situations from the understanding of the flow of biological fluids to the development of soft micro-robots. Here we present a simple measurement technique for the Poisson's ratio of soft micron-sized hydrogels in the presence of a surrounding liquid. This methods relies on the measurement of the deformation in two orthogonal directions of a rectangular hydrogel slab compressed uni-axially inside a microfluidic channel. Due to the in situ character of the method, the sample does not need to be dried, allowing for the measurement of the mechanical properties of swollen hydrogels. Using this method we determine the Poisson's ratio of hydrogel particles composed of polyethylene glycol (PEG) and varying solvents fabricated using a lithography technique. The results demonstrate with high precision the dependence of the hydrogel compressibility on the solvent fraction and character. The method, easy to implement, can be adapted for the measurement of a variety of soft and biological materials.
- arXiv:2003.06601 (replaced) [pdf, other]
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Title: Lattice protein design using Bayesian learningComments: 9 pages, 8 figuresSubjects: Biological Physics (physics.bio-ph); Statistical Mechanics (cond-mat.stat-mech); Machine Learning (cs.LG); Chemical Physics (physics.chem-ph)
A novel protein design method using Bayesian learning is proposed in this work. We consider a posterior probability of amino acid sequences by taking into account water and assuming a prior of sequences. For some instances of a target conformation of a two-dimensional (2D) lattice Hydrophobic-Polar (HP) model, our method successfully finds an amino acid sequence for which the target conformation has a unique ground state. However, the performance was not as good for 3D lattice HP models compared with 2D models. Furthermore, we find a strong linearity between the chemical potential of water and the number of surface residues, thereby revealing the relationship between protein structure and the effect of water molecules. The advantage of our method is that it greatly reduces computation time, because it does not require long calculations for the partition function corresponding to an exhaustive conformational search. As our method uses a general form of Bayesian learning and statistical mechanics and is not limited to lattice HP proteins, the results presented here elucidate some heuristics used successfully in previous protein design methods.
- arXiv:1701.07428 (replaced) [pdf, other]
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Title: A null model for Dunbar's circlesComments: 7 pages, 2 figures, 1 appendixJournal-ref: Physica A 545, 123767 (2020)Subjects: Physics and Society (physics.soc-ph); Statistical Mechanics (cond-mat.stat-mech); Data Analysis, Statistics and Probability (physics.data-an)
An individual's social group may be represented by their ego-network, formed by the links between the individual and their acquaintances. Ego-networks present an internal structure of increasingly large nested layers (or circles) of decreasing relationship intensity, whose size exhibits a precise scaling ratio. Starting from the notion of limited social bandwidth, and assuming fixed costs for the links in each layer, we propose a null model built on a grand-canonical ensemble that generates the observed hierarchical social structure. The observed internal structure of ego-networks becomes a natural outcome to expect when we assume the existence of layers demanding different amounts of resources. In the thermodynamic limit, reached when the number of ego-network copies is large, the specific layer degrees follow a Poisson distribution. We also find that, under certain conditions, equispaced layer costs are necessary to obtain a constant group size scaling. Our model presents interesting analogies to a Bose-Einstein gas, that we briefly discuss. Finally, we fit and compare the model with an empirical social network.
- arXiv:1901.00253 (replaced) [pdf]
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Title: Skyrmion Tubes as Magnonic WaveguidesComments: 36 pages, 55 references, 1 graphical abstract, 7 figures, 3 supplemental figuresJournal-ref: Phys. Rev. Applied 13, 034051 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci)
Various latest experiments have proven the theoretical prediction that domain walls in planar magnetic structures can channel spin waves as outstanding magnonic waveguides, establishing a superb platform for building magnonic devices. Recently, three-dimensional nanomagnetism has been boosted up and become a significant branch of magnetism, because three-dimensional magnetic structures expose a lot of emerging physics hidden behind planar ones and will inevitably provide broader room for device engineering. Skyrmions and antiSkyrmions, as natural three-dimensional magnetic configurations, are not considered yet in the context of spin-wave channeling and steering. Here, we show that skyrmion tubes can act as nonplanar magnonic waveguides if excited suitably. An isolated skyrmion tube in a magnetic nanoprism induces spatially separate internal and edge channels of spin waves; the internal channel has a narrower energy gap, compared to the edge channel, and accordingly can transmit signals at lower frequencies. Additionally, we verify that those spin-wave beams along magnetic nanoprism are restricted to the regions of potential wells. Transmission of spin-wave signals in such waveguides results from the coherent propagation of locally driven eigenmodes of skyrmions, i.e., the breathing and rotational modes. Finally, we find that spin waves along the internal channels are less susceptible to magnetic field than those along the edge channels. Our work will open a new arena for spin-wave manipulation and help bridge skyrmionics and magnonics.
- arXiv:1902.09579 (replaced) [pdf, ps, other]
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Title: Effect of pressure on the order-disorder phase transitions of $B$-cations in $AB'_{1/2}B''_{1/2}$O$_3$ perovskitesComments: 23 pages, 1 figure, 3 tables; Submitted to Acta Crystallographica Section BJournal-ref: Acta Cryst. B75, 1034 (2019)Subjects: Materials Science (cond-mat.mtrl-sci); Strongly Correlated Electrons (cond-mat.str-el)
Perovskite-like oxides $AB'_{1/2}B''_{1/2}$O$_3$ may experience different ordering degrees of $B$-cations, that can be varied by suitable synthesis conditions or post-synthesis treatment. In this work the earlier proposed statistical model of order-disorder phase transitions of $B$-cations is extended to account for the effect of pressure. Depending on composition, pressure is found to either increase or decrease the order-disorder phase transition temperature. The change of transition temperature due to pressure in many cases reaches several hundreds of kelvin at pressures accessible in laboratory, which may significantly change the atomic ordering degree. The work is intended to help determining how pressure influences the degree of atomic ordering and stimulate research of the effect of pressure on atomic order-disorder phase transitions in perovskites.
- arXiv:1904.01838 (replaced) [pdf, ps, other]
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Title: Analytic self-similar solutions of the Kardar-Parisi-Zhang interface growing equation with various noise termComments: 13 Pages and 15 FiguresJournal-ref: Volume 25, Issue 2, 241-256, 2020Subjects: Pattern Formation and Solitons (nlin.PS); Soft Condensed Matter (cond-mat.soft); Statistical Mechanics (cond-mat.stat-mech)
The one-dimensional Kardar-Parisi-Zhang dynamic interface growth equation with the self-similar Ansatz is analyzed. As a new feature additional analytic terms are added. From the mathematical point of view, these can be considered as various noise distribution functions. Six different cases were investigated among others Gaussian, Lorentzian, white or even pink noise. Analytic solutions were evaluated and analyzed for all cases. All results are expressible with various special functions like Kummer, Heun, Whittaker or error functions showing a very rich mathematical structure with some common general characteristics.
- arXiv:1904.09687 (replaced) [pdf, other]
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Title: The Physics of Pair Density WavesAuthors: Daniel F. Agterberg, J. C. Séamus Davis, Stephen D. Edkins, Eduardo Fradkin, Dale J. Van Harlingen, Steven A. Kivelson, Patrick A. Lee, Leo Radzihovsky, John M. Tranquada, Yuxuan WangComments: 43 pages, 16 figures, 236 references. Mildly edited final version to appear in Annual Reviews of Condensed Matter Physics (with improved figures)Journal-ref: Annual Review of Condensed Matter Physics 11, 231 (2020)Subjects: Superconductivity (cond-mat.supr-con)
We review the physics of pair density wave (PDW) superconductors. We begin with a macroscopic description that emphasizes order induced by PDW states, such as charge density wave, and discuss related vestigial states that emerge as a consequence of partial meting of the PDW order. We review and critically discuss the mounting experimental evidence for such PDW order in the cuprate superconductors, the status of the theoretical microscopic description of such order, and the current debate on whether the PDW is a "mother order" or another competing order in the cuprates. In addition, we give an overview of the weak coupling version of PDW order, Fulde-Ferrell-Larkin-Ovchinnikov states, in the context of cold atom systems, unconventional superconductors, and non-centrosymmetric and Weyl materials.
- arXiv:1906.00125 (replaced) [pdf, ps, other]
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Title: Making Birth-Death Processes from Backward Fokker-Planck Equations for Computing Expectations in Langevin SystemsAuthors: Jun OhkuboComments: 6 pages, 2 figuresJournal-ref: J. Phys. Soc. Jpn. 89, 044004 (2020)Subjects: Computational Physics (physics.comp-ph); Statistical Mechanics (cond-mat.stat-mech)
A method to direct evaluation of expectations for Langevin systems (stochastic differential equations) is proposed. The method is based on a birth-death process which is derived using combinations of dummy variables and It{\^o} formula. As a pedagogical example, a double-well system and expectations for sigmoid-type functions are used. It is shown that the proposed method has some merits from computational point of view; only one time-integration for the birth-death process gives expectations for various initial conditions in the original Langevin systems. Furthermore, the same time-integration result is available for computing various center positions of the sigmoid-type functions.
- arXiv:1907.11396 (replaced) [pdf, ps, other]
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Title: Entanglement versus cooling in the system of a driven pair of two-level qubits longitudinally coupled with a boson mode fieldComments: 18 pages, 3 figuresJournal-ref: Journal of Physics B: Atomic, Molecular and Optical Physics 53, 065501 (2020)Subjects: Quantum Physics (quant-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Optics (physics.optics)
The relationship among the entanglement creation within coherently pumped and closely spaced two-level emitters longitudinally coupled with a single-mode boson field, and the subsequent quantum cooling of the boson mode is investigated. Even though the two-level qubits are resonantly driven, we have demonstrated an efficient cooling mechanism well below limits imposed by the thermal background. Furthermore, the cooling effect is accompanied by entanglement of the qubit pair components when the dipole-dipole frequency shift is close to the frequency of the boson mode. The maximum boson mode cooling efficiency realizes on the expense of the entanglement creation. Importantly, this occurs for rather weak external pumping fields protecting the sample from the deteriorations. Finally, the conditions to effectively optimize these effects are described as well.
- arXiv:1909.04733 (replaced) [pdf, other]
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Title: Entanglement production by interaction quenches of quantum chaotic subsystemsAuthors: Jethin J. Pulikkottil (1), Arul Lakshminarayan (2 and 3), Shashi C. L. Srivastava (4 and 5), Arnd Bäcker (6 and 3), Steven Tomsovic (1) ((1) Washington State University Pullman USA, (2) Indian Institute of Technology Madras Chennai India, (3) Max-Planck-Institut für Physik komplexer Systeme Dresden Germany, (4) Variable Energy Cyclotron Centre Kolkata India, (5) Homi Bhabha National Institute Mumbai India, (6) Technische Universität Dresden Dresden Germany)Comments: 18 pages, 16 figures , custom bibstyle fileJournal-ref: Phys. Rev. E 101, 032212 (2020)Subjects: Quantum Physics (quant-ph); Statistical Mechanics (cond-mat.stat-mech); Chaotic Dynamics (nlin.CD)
The entanglement production in bipartite quantum systems is studied for initially unentangled product eigenstates of the subsystems, which are assumed to be quantum chaotic. Based on a perturbative computation of the Schmidt eigenvalues of the reduced density matrix, explicit expressions for the time-dependence of entanglement entropies, including the von Neumann entropy, are given. An appropriate re-scaling of time and the entropies by their saturation values leads a universal curve, independent of the interaction. The extension to the non-perturbative regime is performed using a recursively embedded perturbation theory to produce the full transition and the saturation values. The analytical results are found to be in good agreement with numerical results for random matrix computations and a dynamical system given by a pair of coupled kicked rotors.
- arXiv:1909.07213 (replaced) [pdf, ps, other]
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Title: Continuous time random walks and Lévy walks with stochastic resettingComments: 10 pages, 5 figuresJournal-ref: Phys. Rev. Research 2, 013103 (2020)Subjects: Statistical Mechanics (cond-mat.stat-mech)
Intermittent stochastic processes appear in a wide field, such as chemistry, biology, ecology, and computer science. This paper builds up the theory of intermittent continuous time random walk (CTRW) and L\'{e}vy walk, in which the particles are stochastically reset to a given position with a resetting rate $r$. The mean squared displacements of the CTRW and L\'{e}vy walks with stochastic resetting are calculated, uncovering that the stochastic resetting always makes the CTRW process localized and L\'{e}vy walk diffuse slower. The asymptotic behaviors of the probability density function of L\'evy walk with stochastic resetting are carefully analyzed under different scales of $x$, and a striking influence of stochastic resetting is observed.
- arXiv:1910.12650 (replaced) [pdf, ps, other]
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Title: Dynamical Mean-Field Theory of Strongly Correlated Electron SystemsAuthors: Dieter VollhardtComments: Plenary Lecture held at the International Conference on Strongly Correlated Electron Systems 2019 (SCES 2019), Okayama, Japan, 24.09.2019; to be published in the Proceedings of SCES2019 (JPS Conf. Proc.); 12 pages, 1 figure; typos corrected, references added, all author names in the references written outSubjects: Strongly Correlated Electrons (cond-mat.str-el)
Dynamical Mean-Field Theory (DMFT) has opened new perspectives for the investigation of strongly correlated electron systems and greatly improved our understanding of correlation effects in models and materials. In contrast to Hartree-Fock-type approximations the mean field of DMFT is dynamical, whereby local quantum fluctuations are fully taken into account. DMFT becomes exact in the limit of high spatial dimensions or coordination number. Using DMFT the dynamics of correlated electron systems can be investigated non-perturbatively at all interaction strengths, electron densities and temperatures. By merging density functional theory with DMFT a powerful method for the calculation of the properties of correlated electron materials has become available, which is applicable to bulk systems and heterostructures, including topological states of matter. The inclusion of non-local correlations into DMFT makes it possible to explore unconventional superconductivity and the critical behavior at thermal or quantum phase transitions. By generalizing DMFT to non-equilibrium states also the real-time dynamics of correlated systems can be investigated. In this brief review the foundations and current status of DMFT are discussed along with characteristic physical insights obtained with this approach.
- arXiv:1910.12663 (replaced) [pdf, other]
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Title: Size Dependent Sensitivity of Raman Line-Shape Parameters in Silicon Quantum WireComments: 8 pages, 3 figuresJournal-ref: Adv. Mat. processing Technol. (Taylor & Francis), 2020Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
A comparison of experimentally observed Raman scattering data with Raman line-shapes, generated theoretically using phonon confinement model, has been carried out to understand the sensitivity of different Raman spectral parameters on quantum confinement effect. Size dependent variations of full width at half maximum (FWHM), Raman peak position and asymmetry ratio have been analyzed to establish the sensitivity of their corresponding physical counterparts (phonon life time and dispersion) in confined systems. The comparison has been done in three different confinement regimes namely, weakly, moderately and strongly. Proper reasoning has been assigned for such a variation after validation of the theoretical analysis with the experimental observations. A moderately confined system was created by preparing 6 nm sized Si NSs using metal induced etching. An asymmetrically broadened and red-shifted Raman line-shape was observed which established that all the parameters get affected in moderately confined system. Sensitivity of a given Raman spectral parameters has been shown to be used as a tool to understand the role of external perturbations in a material.
- arXiv:1911.04236 (replaced) [pdf, ps, other]
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Title: Strong anomalous diffusion in two-state process with Lévy walk and Brownian motionComments: 10 pages, 2 figuresJournal-ref: Phys. Rev. Research 2, 013102 (2020)Subjects: Statistical Mechanics (cond-mat.stat-mech)
Strong anomalous diffusion phenomena are often observed in complex physical and biological systems, which are characterized by the nonlinear spectrum of exponents $q\nu(q)$ by measuring the absolute $q$-th moment $\langle |x|^q\rangle$. This paper investigates the strong anomalous diffusion behavior of a two-state process with L\'{e}vy walk and Brownian motion, which usually serves as an intermittent search process. The sojourn times in L\'{e}vy walk and Brownian phases are taken as power law distributions with exponents $\alpha_+$ and $\alpha_-$, respectively. Detailed scaling analyses are performed for the coexistence of three kinds of scalings in this system. Different from the pure L\'{e}vy walk, the phenomenon of strong anomalous diffusion can be observed for this two-state process even when the distribution exponent of L\'{e}vy walk phase satisfies $\alpha_+<1$, provided that $\alpha_-<\alpha_+$. When $\alpha_+<2$, the probability density function (PDF) in the central part becomes a combination of stretched L\'{e}vy distribution and Gaussian distribution due to the long sojourn time in Brownian phase, while the PDF in the tail part (in the ballistic scaling) is still dominated by the infinite density of L\'{e}vy walk.
- arXiv:1911.05382 (replaced) [pdf, other]
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Title: Self-organized bistability and its possible relevance for brain dynamicsComments: 6 figuresJournal-ref: Phys. Rev. Research 2, 013318 (2020)Subjects: Statistical Mechanics (cond-mat.stat-mech); Adaptation and Self-Organizing Systems (nlin.AO); Neurons and Cognition (q-bio.NC)
Self-organized bistability (SOB) is the counterpart of 'self-organized criticality' (SOC), for systems tuning themselves to the edge of bistability of a discontinuous phase transition, rather than to the critical point of a continuous one. The equations defining the mathematical theory of SOB turn out to bear strong resemblance to a (Landau-Ginzburg) theory recently proposed to analyze the dynamics of the cerebral cortex. This theory describes the neuronal activity of coupled mesoscopic patches of cortex, homeostatically regulated by short-term synaptic plasticity. The theory for cortex dynamics entails, however, some significant differences with respect to SOB, including the lack of a (bulk) conservation law, the absence of a perfect separation of timescales and, the fact that in the former, but not in the second, there is a parameter that controls the overall system state (in blatant contrast with the very idea of self-organization). Here, we scrutinize --by employing a combination of analytical and computational tools-- the analogies and differences between both theories and explore whether in some limit SOB can play an important role to explain the emergence of scale-invariant neuronal avalanches observed empirically in the cortex. We conclude that, actually, in the limit of infinitely slow synaptic-dynamics, the two theories become identical, but the timescales required for the self-organization mechanism to be effective do not seem to be biologically plausible. We discuss the key differences between self-organization mechanisms with/without conservation and with/without infinitely separated timescales. In particular, we introduce the concept of 'self-organized collective oscillations' and scrutinize the implications of our findings in neuroscience, shedding new light into the problems of scale invariance and oscillations in cortical dynamics.
- arXiv:1911.10125 (replaced) [pdf, other]
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Title: Entanglement spectroscopy of chiral edge modes in the Quantum Hall effectComments: 18 pages, 8 figuresJournal-ref: Phys. Rev. B 101, 115136 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el); Statistical Mechanics (cond-mat.stat-mech); Mathematical Physics (math-ph)
We investigate the entanglement entropy in the Integer Quantum Hall effect in the presence of an edge, performing an exact calculation directly from the microscopic two-dimensional wavefunction. The edge contribution is shown to coincide exactly with that of a chiral Dirac fermion, and this correspondence holds for an arbitrary collection of intervals. In particular for a single interval the celebrated conformal formula is recovered with left and right central charges $c+\bar{c} =1$. Using Monte-Carlo techniques we establish that this behavior persists for strongly interacting systems such as Laughlin liquids. This illustrates how entanglement entropy is not only capable of detecting the presence of massless degrees of freedom, but also of pinpointing their position in real space, as well as elucidating their nature.
- arXiv:1912.02936 (replaced) [pdf, other]
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Title: Laser modulation of superconductivity in a cryogenic widefield nitrogen-vacancy microscopeAuthors: Scott E. Lillie, David A. Broadway, Nikolai Dontschuk, Sam C. Scholten, Brett C. Johnson, Sebastian Wolf, Stephan Rachel, Lloyd C. L. Hollenberg, Jean-Philippe TetienneJournal-ref: Nano Lett. 20, 1855-1861 (2020)Subjects: Superconductivity (cond-mat.supr-con); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Microscopic imaging based on nitrogen-vacancy (NV) centres in diamond, a tool increasingly used for room-temperature studies of condensed matter systems, has recently been extended to cryogenic conditions. However, it remains unclear whether the technique is viable for imaging temperature-sensitive phenomena below 10 K given the inherent laser illumination requirements, especially in a widefield configuration. Here we realise a widefield NV microscope with a field of view of 100 $\mu$m and a base temperature of 4 K, and use it to image Abrikosov vortices and transport currents in a superconducting Nb film. We observe the disappearance of vortices upon increase of laser power and their clustering about hot spots upon decrease, indicating that laser powers as low as 1 mW (4 orders of magnitude below the NV saturation) are sufficient to locally quench the superconductivity of the film ($T_c = 9$ K). This significant local heating is confirmed by resistance measurements, which reveal the presence of large temperature gradients (several K) across the film. We then investigate the effect of such gradients on transport currents, where the current path is seen to correlate with the temperature profile even in the fully superconducting phase. In addition to highlighting the role of temperature inhomogeneities in superconductivity phenomena, this work establishes that, under sufficiently low laser power conditions, widefield NV microscopy enables imaging over mesoscopic scales down to 4 K with a submicrometer spatial resolution, providing a new platform for real-space investigations of a range of systems from topological insulators to van der Waals ferromagnets.
- arXiv:1912.05367 (replaced) [pdf, other]
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Title: Robust cycloid crossover driven by anisotropy in the skyrmion host GaV$_\mathbf{4}$S$_\mathbf{8}$Authors: E. M. Clements, R. Das, G. Pokharel, M. H. Phan, A. D. Christianson, D. Mandrus, J. C. Prestigiacomo, M. S. Osofsky, H. SrikanthComments: 12 pages, 9 figures, minor figure corrections, expanded explanations in Secs. I & IIIB.,CJournal-ref: Phys. Rev. B 101, 094425 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci); Strongly Correlated Electrons (cond-mat.str-el)
We report on the anomalous magnetization dynamics of the cycloidally-modulated spin textures under the influence of uniaxial anisotropy in multiferroic $\mathrm{GaV_4S_8}$. The temperature and field dependence of the linear ac susceptibility [$\chi_{1\omega}^{\prime}(T,H)$], ac magnetic loss [$\chi_{1\omega}^{\prime\prime}(T,H)$], and nonlinear ac magnetic response [$M_{3\omega}(T,H)$] are examined across the magnetic phase diagram in the frequency range $f = 10-10000$ Hz. According to recent theory, skyrmion vortices under axial crystal symmetry are confined along specific orientations, resulting in enhanced robustness against oblique magnetic fields and altered spin dynamics. We characterize the magnetic response of each spin texture and find that the dynamic rigidity of the N\'eel skyrmion lattice appears enhanced compared to Bloch-type skyrmions in cubic systems, even in the multidomain state. Anomalous $M_{3\omega}$ and strong dissipation emerge over the same phase regime where strong variations in the cycloid pitch were observed on lowering temperature in recent small-angle neutron scattering experiments [White et al., Phys. Rev. B 97, 020401(R) (2018)]. Here, we show that strong anisotropy also drives an extended crossover of the zero-field cycloid texture in $\mathrm{GaV_4S_8}$. The frequency dependence of these dynamic signatures is consistent with that of a robust anharmonic spin texture exhibiting a correlated domain arrangement. The results underpin the essential role of magnetic anisotropy in enhancing the rigidity of topological spin textures for diverse applications.
- arXiv:2001.00044 (replaced) [pdf, ps, other]
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Title: Non-Hermitian impurities in Dirac systemsComments: 14 pages, 13 figuresJournal-ref: Phys. Rev. Research 2, 013325 (2020)Subjects: Disordered Systems and Neural Networks (cond-mat.dis-nn); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Optics (physics.optics); Quantum Physics (quant-ph)
Quasiparticle states in Dirac systems with complex impurity potentials are investigated. It is shown that an impurity site with loss leads to a nontrivial distribution of the local density of states (LDOS). While the real part of defect potential induces a well-pronounced peak in the density of states (DOS), the DOS is either weakly enhanced at small frequencies or even forms a peak at the zero frequency for a lattice in the case of non-Hermitian impurity. As for the spatial distribution of the LDOS, it is enhanced in the vicinity of impurity but shows a dip at a defect itself when the potential is sufficiently strong. The results for a two-dimensional hexagonal lattice demonstrate the characteristic trigonal-shaped profile for the LDOS. The latter acquires a double-trigonal pattern in the case of two defects placed at neighboring sites. The effects of non-Hermitian impurities could be tested both in photonic lattices and certain condensed matter setups.
- arXiv:2001.09713 (replaced) [pdf, other]
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Title: First-principles-based calculation of branching ratio for 5$\boldsymbol{d}$, 4$\boldsymbol{d}$, and 3$\boldsymbol{d}$ transition metal systemsSubjects: Strongly Correlated Electrons (cond-mat.str-el); Computational Physics (physics.comp-ph)
A new first-principles computation scheme to calculate `branching ratio' has been applied to various $5d$, $4d$, and $3d$ transition metal elements and compounds. This recently suggested method is based on a theory which assumes the atomic core hole interacting barely with valence electrons. While it provides an efficient way to calculate the experimentally measurable quantity without generating spectrum itself, its reliability and applicability should be carefully examined especially for the light transition metal systems. Here we select 36 different materials and compare the calculation results with experimental data. It is found that our scheme well describes 5$d$ and 4$d$ transition metal systems whereas, for 3$d$ materials, the difference between the calculation and experiment is quite significant. It is attributed to the neglect of core-valence interaction whose energy scale is comparable with the spin-orbit coupling of core $p$ orbitals.
Crosses
- arXiv:2003.08029 (cross-list from cond-mat.mes-hall) [pdf, ps, other]
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Title: Topological degeneracy in Ising chain induced by dissipationComments: 7 pages, 2 figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Strongly Correlated Electrons (cond-mat.str-el); Quantum Physics (quant-ph)
The groundstate degeneracy of quantum spin system is a characteristic of non-trivial topology, when it is gapped and robust against disordered perturbation. The corresponding quantum phase transition (QPT) is usually driven by a real parameter. We study a non-Hermitian Ising chain with two transverse fields, one real another imaginary, based on the exact solution and numerical simulation. We show that topological degeneracy still exists, and can be obtained by an imaginary transverse field from a topologically trivial phase of a Hermitian system. The topological degeneracy is robust against random imaginary field, and therefore expected to be immune to disordered dissipation from the spontaneous decay in experiment. The underlying mechanism is the nonlocal symmetry, which emerges only in thermodynamic limit and unifies two categories of QPTs in quantum spin system, rooted from topological order and symmetry breaking, respectively.
Mon, 23 Mar 2020
- arXiv:2003.08940 [pdf, ps, other]
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Title: Theory of Electronic Relaxation in solution with ultra-short sink of different shapes: An exact analytical solutionSubjects: Statistical Mechanics (cond-mat.stat-mech)
We propose a very simple one dimensional analytically solvable model for understanding the problem of electronic relaxation of molecules in solution. This problem is modeled by a particle diffusing under the influence of parabolic potential in presence of a sink of ultra-short width. The diffusive motion is described by the Smoluchowski equation and shape of the sink is represented by 1) ultra-short Gaussian, 2) ultra-short exponential and 3) ultra-short rectangular function at arbitrary position. Rate constants are found to be sensitive to the shape of the sink function, even though the width of the sink is too small. This model is of considerable importance as a realistic model in comparison with the point sink model for understanding the problem of electronic relaxation of a molecule in solution.
- arXiv:2003.08944 [pdf, other]
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Title: Studying dynamics in two-dimensional quantum lattices using tree tensor network statesSubjects: Strongly Correlated Electrons (cond-mat.str-el); Quantum Physics (quant-ph)
We analyze and discuss convergence properties of a numerically exact algorithm tailored to study the dynamics of interacting two-dimensional lattice systems. The method is based on the application of the time-dependent variational principle in a manifold of binary and quaternary Tree Tensor Network States. The approach is found to be competitive with existing matrix product state approaches. We discuss issues related to the convergence of the method, which could be relevant to a broader set of numerical techniques used for the study of two-dimensional systems.
- arXiv:2003.08945 [pdf, other]
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Title: Observation of gauge invariance in a 71-site quantum simulatorAuthors: Bing Yang, Hui Sun, Robert Ott, Han-Yi Wang, Torsten V. Zache, Jad C. Halimeh, Zhen-Sheng Yuan, Philipp Hauke, Jian-Wei PanSubjects: Quantum Gases (cond-mat.quant-gas); High Energy Physics - Lattice (hep-lat); High Energy Physics - Phenomenology (hep-ph); Atomic Physics (physics.atom-ph); Quantum Physics (quant-ph)
The modern description of elementary particles is built on gauge theories. Such theories implement fundamental laws of physics by local symmetry constraints, such as Gauss's law in the interplay of charged matter and electromagnetic fields. Solving gauge theories by classical computers is an extremely arduous task, which has stimulated a vigorous effort to simulate gauge-theory dynamics in microscopically engineered quantum devices. Previous achievements used mappings onto effective models to integrate out either matter or electric fields, or were limited to very small systems. The essential gauge symmetry has not been observed experimentally. Here, we report the quantum simulation of an extended U(1) lattice gauge theory, and experimentally quantify the gauge invariance in a many-body system of 71 sites. Matter and gauge fields are realized in defect-free arrays of bosonic atoms in an optical superlattice. We demonstrate full tunability of the model parameters and benchmark the matter-gauge interactions by sweeping across a quantum phase transition. Enabled by high-fidelity manipulation techniques, we measure Gauss's law by extracting probabilities of locally gauge-invariant states from correlated atom occupations. Our work provides a way to explore gauge symmetry in the interplay of fundamental particles using controllable large-scale quantum simulators.
- arXiv:2003.08956 [pdf, other]
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Title: Transport Signature of the Magnetic Berezinskii-Kosterlitz-Thouless TransitionComments: 6 pages, 2 figures, 1 page of Supplemental MaterialSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Strongly Correlated Electrons (cond-mat.str-el)
The theory of the Berezinskii-Kosterlitz-Thouless (BKT) phase transition was formulated to describe the 2D phase transition of easy-plane magnets as well as 2D superconductors and superfluids. The BKT transition being topological in nature, i.e. not characterized by a local order parameter, its detection has been challenging. The BKT transitions in the latter cases have been observed in experiments, much of which involves transport signatures, such as the current-voltage relation being non-linear below the BKT temperature and linear above the BTK temperature. By contrast, the experimental study of the solid-state 2D magnetic material emerged only in the last few years, with an active ongoing effort to demonstrate the 2D magnetic phase transition. The accompanied recent development of spin-transport measurements offers a tantalizing opportunity to discover novel transport phenomena of spin, which should be expected as the spin, unlike the particle number, is not conserved. In this Letter, we show that this non-conservation of spin leads to a distinct signature in spin transport through 2D easy-plane magnets at the BKT transition, exhibiting a crossover between the superfluid spin transport and the exponentially decaying spin transport. We also put forward an experimental proposal for the detection of the predicted spin-transport signature in the van der Waals easy-plane magnetic materials such as the monolayer NiPS$_3$ and CrCl$_3$.
- arXiv:2003.08957 [pdf, other]
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Title: Universal relationship between the energy scales of the pseudogap phase, the superconducting state and the charge density wave order in copper oxide superconductorsAuthors: B. Loret, N. Auvray, G. D. Gu, A. Forget, D. Colson, M. Cazayous, Y. Gallais, I. Paul, M. Civelli, A. SacutoComments: 11 pages and 9 figuresSubjects: Superconductivity (cond-mat.supr-con)
We report the hole doping dependencies of the pseudogap phase energy scale, $2\Delta_{\rm PG}$, the anti-nodal (nodal) superconducting energy scales $2\Delta^{AN}_{\rm SC}$ ($2\Delta^{N}_{\rm SC}$) and the charge density wave energy scale, $2\Delta_{\rm CDW}$. They have been extracted from the electronic Raman responses of distinct copper oxide families. For all the cuprates studied, we reveal universal doping dependencies which suggest that $2\Delta_{\rm PG}$, $2\Delta^{AN}_{\rm SC}$ and $2\Delta_{\rm CDW}$ are governed by common microscopic interactions and that these interactions become relevant well above the superconducting transition at $T_c$. In sharp contrast, $2\Delta^N_{\rm SC}$ tracks the doping dependence of $T_c$, appearing to be controlled by a different kind of interactions than the energy scales above.
- arXiv:2003.08962 [pdf, ps, other]
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Title: Microwave Applications of Photonic Topological InsulatorsSubjects: Applied Physics (physics.app-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
This Perspective examines the emerging applications of photonic topological insulators (PTIs) in the microwave domain. The introduction of topological protection of light has revolutionized the traditional perspective of wave propagation through the demonstration of backscatter-free waveguides in the presence of sharp bending and strong structural defects. The pseudospin degree of freedom of light enables the invention of unprecedented topological photonic devices with useful functionalities. Our aim is to present a brief introduction of recent developments in microwave PTI demonstrations. We give a clear comparison of different PTI realizations, summarize the key features giving rise to topological protection, and present a discussion of advantages and disadvantages of PTI technology compared to existing microwave device technology. We conclude with forward-looking perspectives of how the advantages of this technology can best be exploited.
- arXiv:2003.08970 [pdf, other]
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Title: Nonlinear optical study of commensurability effects in graphene-hBN heterostructuresAuthors: E. A. Stepanov, S. V. Semin, C. R. Woods, M. Vandelli, A. V. Kimel, K. S. Novoselov, M. I. KatsnelsonSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci)
Second-order nonlinear optical response allows to detect different properties of the system associated with the inversion symmetry breaking. Here, we use a second harmonic generation effect to investigate the alignment of a graphene/hexagonal Boron Nitride heterostructure. To achieve that, we activate a commensurate-incommensurate phase transition by a thermal annealing of the sample. We find that this structural change in the system can be directly observed through a strong modification of a nonlinear optical signal. This result reveals the potential of a second harmonic generation technique for probing structural properties of layered systems.
- arXiv:2003.08973 [pdf, other]
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Title: Topology of atomically thin soft ferroelectric membranes at finite temperatureComments: Originally submitted on August 27, 2019Journal-ref: Phys. Rev. B 101, 184101 (2020)Subjects: Soft Condensed Matter (cond-mat.soft); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
One account of two-dimensional (2D) structural transformations in 2D ferroelectrics predicts an evolution from a structure with Pnm2$_1$ symmetry into a structure with square P4/nmm symmetry and is consistent with experimental evidence, while another argues for a transformation into a structure with rectangular Pnmm symmetry. An analysis of the assumptions made in these models is provided here, and six fundamental results concerning these transformations are contributed as follows: (i) Softened phonon modes produce rotational modes in these materials. (ii) The transformation to a structure with P4/nmm symmetry occurs at the lowest critical temperature $T_c$. (iii) The hypothesis that one unidirectional optical vibrational mode underpins the 2D transformation is unwarranted. (iv) Being successively more constrained, a succession of critical temperatures ($T_c<T_c'<T_c''$) occurs in going from molecular dynamics calculations with the NPT and NVT ensembles onto the model with unidirectional oscillations. (v) The choice of exchange-correlation functional impacts the estimate of the critical temperature. (vi) Crucially, the correct physical picture of these transformations is one in which rotational modes confer a topological character to the 2D transformation via the proliferation of vortices.
- arXiv:2003.08977 [pdf, other]
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Title: Symmetry breaking on icosahedral lattices of dipolesComments: 7 figuresSubjects: Soft Condensed Matter (cond-mat.soft)
Symmetry is one of the key properties of spherical assemblies in biological and complex matter, and examples include viral capsids, virus-like particles, and nanocontainers designed for various purposes. Anisotropic interactions between building blocks of these assemblies, such as dipole-dipole interaction, can induce symmetry breaking, aid self-assembly, and affect the stability of the structures. We investigate a system of long-range interacting dipole arrangements on a sphere, focusing specifically on their symmetry properties. We find ground states of dipoles positioned on Caspar-Klug icosahedrally symmetric spherical lattices in relation to different symmetry constraints. We analyze the stability of highly symmetric metastable states, their symmetry breaking into subsymmetries of the icosahedral symmetry group, and present a phase diagram of symmetries with respect to lattice parameters. Furthermore, we show how the symmetry of any dipole configuration can be analyzed using vector spherical harmonics. The observed relationship between positional order and dipole-induced symmetry breaking hints at ways of fine-tuning the structure of spherical assemblies and their design.
- arXiv:2003.08979 [pdf, other]
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Title: Bridging transitions and capillary forces for colloids in a slitSubjects: Soft Condensed Matter (cond-mat.soft)
Capillary bridges can form between colloids immersed in a two phase fluid, e.g., in a binary liquid mixture, if the surface of the colloids prefers the species other than the one favored in the bulk liquid. Here, we study the formation of liquid bridges induced by confining colloids to a slit, with the slit walls having a preference opposite to the one of the colloid surface. Using mean field theory, we show that there is a line of first-order phase transitions between the bridge and the no-bridge states, which ends at a critical point. By decreasing the slit width, this critical point is shifted towards smaller separations between the colloids. However, at very small separations, and far from criticality, we observe only a minor influence of the slit width on the location of the transition. Monte Carlo simulations of the Ising model, which mimics incompressible binary liquid mixtures, confirm the occurrence of the bridging transitions, as manifested by the appearance of bistable regions where both the bridge and the no-bridge configurations are (meta)stable. Interestingly, we find no bistability in the case of small colloids, but we observe a sharpening of the transition when the colloid size increases. In addition, we demonstrate that the capillary force acting between the colloids can depend sensitively on the slit width, and varies drastically with temperature, thus achieving strengths orders of magnitude higher than at criticality of the fluid.
- arXiv:2003.08986 [pdf, other]
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Title: Evidence of Fermi-Surface Reconstruction at the Metamagnetic Transition of the Strongly Correlated Superconductor UTe2Authors: Qun Niu, Georg Knebel, Daniel Braithwaite, Dai Aoki, Gérard Lapertot, Michal Vališka, Gabriel Seyfarth, William Knafo, Toni Helm, Jean-Pascal Brison, Jacques Flouquet, Alexandre PourretComments: 5 figures in the main text; 9 figures in the supplemental materialSubjects: Strongly Correlated Electrons (cond-mat.str-el); Superconductivity (cond-mat.supr-con)
Thermoelectric power ($S$) and Hall effect ($R_\mathrm{H}$) measurements on the paramagnetic superconductor UTe$_2$ with magnetic field applied along the hard magnetization $b$-axis are reported. The first order nature of the metamagnetic transition at $H_\mathrm{m}=H^b_\mathrm{c2}=35$~T leads to drastic consequences on $S$ and $R_\mathrm{H}$. In contrast to the field dependence of the specific heat in the normal state through $H_\mathrm{m}$, $S(H)$ is not symmetric with respect to $H_\mathrm{m}$. This implies a strong interplay between ferromagnetic (FM) fluctuations and a Fermi-surface reconstruction at $H_\mathrm{m}$. $R_\mathrm{H}$ is very well described by incoherent skew scattering above the coherence temperature $T_\mathrm{m}$ corresponding roughly to the temperature of the maximum in the susceptibility $T_{\chi_\mathrm{max}}$ and coherent skew scattering at lower temperatures. The discontinuous field dependence of both, $S(H)$ and the ordinary Hall coefficient $R_0$, at $H_\mathrm{m}$ and at low temperature, provides evidence of a change in the band structure at the Fermi level.
- arXiv:2003.08987 [pdf, other]
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Title: Chiral zigzag modes and flatbands in network models of twisted bilayer grapheneComments: 5 + 4 pages, 6 + 4 figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We construct a phenomenological scattering theory for the triangular network of valley Hall states that arises in twisted bilayer graphene under interlayer bias. Crucially, our network model includes scattering between different valley Hall states within the same valley and spin. We show that in the absence of forward scattering, symmetries reduce the network model to a single parameter that interpolates between a nested Fermi surface and flatbands, which can be understood in terms of one-dimensional chiral zigzag modes and closed triangular orbits, respectively. We demonstrate how unitarity and symmetry constrain the couplings between zigzag modes, which has important implications on the nature of interference oscillations observed in experiments.
- arXiv:2003.09001 [pdf, other]
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Title: Modeling of stimuli-responsive nanoreactors: rational rate control towards the design of colloidal enzymesComments: 13 pages, 9 figuresJournal-ref: Mol. Syst. Des. Eng., 2020, Advance ArticleSubjects: Chemical Physics (physics.chem-ph); Soft Condensed Matter (cond-mat.soft)
In modern applications of heterogeneous liquid-phase nanocatalysis, the catalysts (e.g., metal nanoparticles) need to be typically affixed to a colloidal carrier system for stability and easy handling. "Passive carriers" (e.g., simple polyelectrolytes) serve for a controlled synthesis of the nanoparticles and prevent coagulation during catalysis. Recently, however, hybrid conjugates of nanoparticles and synthetic thermosensitive polymers have been developed that enable to change the catalytic activity of the nanoparticles by external triggers. In particular, nanoparticles embedded in a stimuli-responsive network made from poly(N-isopropylacrylamide) (PNIPAM) have become the most-studied examples of such hybrids. It has been demonstrated that the permeability of the polymer network and thus the reactant flux can be switched and controlled by external stimuli. Such "active carriers" may thus be viewed as true nanoreactors that open up new design routes in nano-catalysis and elevate synthesis to create highly selective, programmable "colloidal enzymes". However, only a comprehensive understanding of these materials on all time and length scales can lead to a rational design of future, highly functional materials. Here we review the current state of the theoretical and multi-scale simulation approaches, aiming at a fundamental understanding of these nanoreactors. In particular, we summarize a theoretical approach for reaction rates of surface-catalyzed bimolecular reactions in responsive nanoreactors in terms of the key material parameters, the polymer shell permeability P and the reactant partition ratio K. We discuss recent computer simulation studies of both atomistic and coarse-grained polymer models in which these quantities have been characterized in some detail. We conclude with an outlook on selected open questions and future theoretical challenges in nanoreactor modeling.
- arXiv:2003.09014 [pdf, ps, other]
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Title: Finite temperature and quench dynamics in the Transverse Field Ising Model from form factor expansionsComments: 48 pagesSubjects: Statistical Mechanics (cond-mat.stat-mech); Mathematical Physics (math-ph); Quantum Physics (quant-ph)
We consider the problems of calculating the dynamical order parameter two-point function at finite temperatures and the one-point function after a quantum quench in the transverse field Ising chain. Both of these can be expressed in terms of form factor sums in the basis of physical excitations of the model. We develop a general framework for carrying out these sums based on a decomposition of form factors into partial fractions, which leads to a factorization of the multiple sums and permits them to be evaluated asymptotically. This naturally leads to systematic low density expansions. At late times these expansions can be summed to all orders by means of a determinant representation. Our method has a natural generalization to semi-local operators in interacting integrable models.
- arXiv:2003.09036 [pdf, other]
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Title: Computational Design of Stable and Highly Ion-conductive Materials using Multi-objective Bayesian Optimization: Case Studies on Diffusion of Oxygen and LithiumSubjects: Computational Physics (physics.comp-ph); Materials Science (cond-mat.mtrl-sci)
Ion-conducting solid electrolytes are widely used for a variety of purposes. Therefore, designing highly ion-conductive materials is in strongly demand. Because of advancement in computers and enhancement of computational codes, theoretical simulations have become effective tools for investigating the performance of ion-conductive materials. However, an exhaustive search conducted by theoretical computations can be prohibitively expensive. Further, for practical applications, both dynamic conductivity as well as static stability must be satisfied at the same time. Therefore, we propose a computational framework that simultaneously optimizes dynamic conductivity and static stability; this is achieved by combining theoretical calculations and the Bayesian multi-objective optimization that is based on the Pareto hyper-volume criterion. Our framework iteratively selects the candidate material, which maximizes the expected increase in the Pareto hyper-volume criterion; this is a standard optimality criterion of multi-objective optimization. Through two case studies on oxygen and lithium diffusions, we show that ion-conductive materials with high dynamic conductivity and static stability can be efficiently identified by our framework.
- arXiv:2003.09048 [pdf, other]
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Title: Surface response of a polymer network: Semi-infinite networkComments: 14 pagesJournal-ref: Langmuir 36, 3981-3987 (2020)Subjects: Soft Condensed Matter (cond-mat.soft); Fluid Dynamics (physics.flu-dyn)
We study theoretically the surface response of a semi-infinite viscoelastic polymer network using the two-fluid model. We focus on the overdamped limit and on the effect of the network's intrinsic length scales. We calculate the decay rate of slow surface fluctuations, and the surface displacement in response to a localized force. Deviations from the large-scale continuum response are found at length scales much larger than the network's mesh size. We discuss implications for surface scattering and microrheology. We provide closed-form expressions that can be used for surface microrheology -- the extraction of viscoelastic moduli and intrinsic length scales from the motions of tracer particles lying on the surface without doping the bulk material.
- arXiv:2003.09050 [pdf, other]
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Title: Density-matrix based Extended Lagrangian Born-Oppenheimer Molecular DynamicsAuthors: Anders M. N. NiklassonComments: 25 pages, 2 figuresSubjects: Computational Physics (physics.comp-ph); Other Condensed Matter (cond-mat.other); Chemical Physics (physics.chem-ph)
Extended Lagrangian Born-Oppenheimer molecular dynamics [{\em Phys.\ Rev.\ Lett.\ } {\bf 2008}, {\em 100}, 123004] is presented for Hartree-Fock theory, where the extended electronic degrees of freedom are represented by a density matrix, including fractional occupation numbers at elevated electronic temperatures. In contrast to regular direct Born-Oppenheimer molecular dynamics simulations, no iterative self-consistent field optimization is required prior to the force evaluations. To sample regions of the potential energy landscape where the gap is small or vanishing, which leads to particular convergence problems in regular direct Born-Oppenheimer molecular dynamics simulations, an adaptive integration scheme for the extended electronic degrees of freedom is presented. The integration scheme is based on a tunable, low-rank approximation of a fourth-order kernel, ${\cal K}$, that determines the metric tensor, ${\cal T}\equiv {\cal K}^T{\cal K}$, used in the extended harmonic oscillator of the Lagrangian that generates the dynamics of the electronic degrees of freedom. The formulation and algorithms provide a general guide to implement extended Lagrangian Born-Oppenheimer molecular dynamics for quantum chemistry, density functional theory, and semiempirical methods using a density matrix formalism.
- arXiv:2003.09051 [pdf]
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Title: Spin-orbit-coupled metal candidate PbRe2O6Authors: Satoshi Tajima, Daigorou Hirai, Takeshi Yajima, Daisuke Nishio-Hamane, Yasuhito Matsubayashi, Zenji HiroiSubjects: Strongly Correlated Electrons (cond-mat.str-el)
We study the lead rhenium oxide PbRe2O6 as a candidate spin-orbit-coupled metal (SOCM), which has attracted much attention as a testing ground for studying unconventional Fermi liquid instability associated with a large spin-orbit interaction. The compound comprises a stack of modulated honeycomb lattices made of Re5+ (5d2) ions in a centrosymmetric R-3m structure at room temperature. Resistivity, magnetic susceptibility, and heat capacity measurements using single crystals reveal two successive first-order phase transitions at Ts1 = 265 K and Ts2 = 123 K. At Ts1, the magnetic susceptibility is enormously reduced and a structural transition to a monoclinic structure takes place, while relatively small changes are observed at Ts2. Surprisingly, PbRe2O6 bears a close resemblance to another SOCM candidate Cd2Re2O7 despite crucial differences in the crystal structure and probably in the electronic structure, suggesting that PbRe2O6 is an SOCM.
- arXiv:2003.09056 [pdf, other]
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Title: Phase Diagram of the Dynamics of a Precessing Qubit under Quantum MeasurementComments: 8 pages, 4 figuresSubjects: Quantum Physics (quant-ph); Statistical Mechanics (cond-mat.stat-mech)
We study the phase transitions induced by sequentially measuring a single qubit precessing under an external transverse magnetic field. Under projective quantum measurement, the probability distribution of the measurement outcomes can be mapped exactly to the thermodynamic probability distribution of a one-dimensional Ising model, whose coupling can be varied by the magnetic field from ferromagnetic to anti-ferromagnetic. For the general case of sequential quantum measurement,we develop a fast and exact algorithm to calculate the probability distribution function of the ferromagnetic order and anti-ferromagnetic order, and a phase diagram is obtained in the parameter space spanned by the measurement strength and magnetic field strength. The mapping to a long-range interacting Ising model is obtained in the limit of small measurement strength. Full counting statistical approach is applied to understand the phase diagram, and to make connections with the topological phase transition that is characterized by the braid group. This work deepens the understanding of phase transitions induced by quantum measurement, and may provide a new method to characterize and steer the quantum evolution.
- arXiv:2003.09059 [pdf]
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Title: Ultra-slow sound in non-resonant meta-aerogelSubjects: Applied Physics (physics.app-ph); Materials Science (cond-mat.mtrl-sci)
The manipulation of sound with acoustic metamaterials is a field of intense research, where interaction via resonance is a common application despite the significant disadvantages. We propose a novel procedure for introducing well-designed coupling interfaces with a cell size of less than 10 nm into an ultra-soft porous medium, to prepare a meta-aerogel, where the sound propagation is significantly delayed in a non-resonant mode. The resultant sound velocity is shown as a scaling law with the mass density and the mass fraction ratio of the components, in accordance with our analytical model. We have prepared a meta-aerogel with the slowest sound velocity of 62 m/s. To the best of our knowledge, this is the lowest value in compact solid materials, with a prospect of further slowing down by our procedure. The development of such meta-aerogels can facilitate key applications in acoustic metamaterials intended to employ non-resonant type slow sound (or phase delay). Examples of the latter include deep subwavelength meta-surface and other focused imaging or transformation acoustics that require a high contrast of sound velocity.
- arXiv:2003.09104 [pdf, other]
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Title: Quantum Fluctuations in the Non-Fermi Liquid System CeCo$_{2}$Ga$_{8}$ Investigated Using $μ$SRAuthors: A. Bhattacharyya, D. T. Adroja, J. S. Lord, L. Wang, Y. Shi, K. Panda, H. Luo, A. M. StrydomComments: 6 pages, 2 figuresSubjects: Strongly Correlated Electrons (cond-mat.str-el); Materials Science (cond-mat.mtrl-sci)
Reduced dimensionality offers a crucial information in deciding the type of the quantum ground state in heavy fermion materials. Here we have examined stoichiometric CeCo$_{2}$Ga$_{8}$ compound, which crystallizes in a quasi-one-dimensional crystal structure with Ga-Ce-Co chains along the $c$-axis. The low-temperature behavior of magnetic susceptibility ($\chi\sim-\ln T$), heat capacity ($C_p/T\sim-\ln T$), and resistivity ($\rho\sim T^{n}$) firmly confirm the non-Fermi liquid ground state of CeCo$_{2}$Ga$_{8}$. We studied the low-energy spin dynamics of CeCo$_{2}$Ga$_{8}$ compound utilizing zero field (ZF-) and longitudinal field (LF-) muon spin relaxation ($\mu$SR) measurements. ZF-$\mu$SR measurement reveals the absence of long-range magnetic ordering down to 70 mK, and interestingly below 1 K, the electronic relaxation rate sharply rises, intimating the appearance of low energy quantum spin fluctuations in CeCo$_{2}$Ga$_{8}$.
- arXiv:2003.09105 [pdf, other]
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Title: Anisotropy of the transport properties of NdFeAs(O,F) thin films grown on vicinal substratesJournal-ref: Superconductor Science and Technology 33, 044016 (2020)Subjects: Superconductivity (cond-mat.supr-con)
NdFeAs(O,F) thin films having different fluorine contents were grown on 5 deg. or 10 deg. vicinal cut MgO and CaF2 single crystalline substrates by molecular beam epitaxy. Structural characterisations by reflection high-energy electron diffraction and x-ray diffraction confirmed the epitaxial growth of NdFeAs(O,F). The resistivities of the ab-plane and along the c-axis were derived from the resistivity measurements in the longitudinal and transversal directions. The c-axis resistivity was always higher than the ab-plane resistivity, resulting from the anisotropic electronic structure. The resistivity anisotropy at 300 K was almost constant in the range of 50-90 irrespective of the F content. On the other hand, the resistivity anisotropy at 56 K showed a strong fluorine dependence: the resistivity anisotropy was over 200 for the films with optimum F contents (superconducting transition temperature Tc around 50 K), whereas the resistivity anisotropy was around 70 for the films in the under-doped regime (Tc between 35 and 45 K). The mass anisotropy are the effective masses along the c-axis and on the ab-plane) close to Tc derived from the anisotropic Ginzburg-Landau approach using the angular-dependency of the ab-plane resistivity was in the range from 2 to 5. On the assumption that the square of the mass anisotropy is equal to the resistivity anisotropy, those values are small compared to the normal state anisotropy.
- arXiv:2003.09128 [pdf, other]
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Title: A ternary map of Ni-Mn-Ga Heusler alloys from ab initio calculationsSubjects: Materials Science (cond-mat.mtrl-sci)
In the present work, the aspects of magnetic and structural properties of Ni-Mn-Ga alloys are described in the framework of fist-principles approach and mapped into ternary composition diagrams. The stable atomic arrangement and magnetic alignment for compositions with cubic austenite and tetragonal martensite structures across phase diagrams are predicted. It is shown that Ni- and Ga-rich compositions possess the regular Heusler structure in contrast to Mn-rich compositions with inverse Heusler structure as favorable one. Compositions with unstable austenite structure are concentrated in the left and right sides of diagram whereas compositions with unstable martensite structure are located in the low-middle part of diagram. The magnetic phase diagrams showing regions with the ferromagnetic order and the complex ferrimagnetic order for austenitic and martensitic compositions are obtained. The results of calculations are in a good agreement with available experimental data.
- arXiv:2003.09131 [pdf, other]
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Title: Electron Spin Resonance with up to 20 Spin Sensitivity Measured using a Superconducting Flux QubitComments: 4 pages, 4 figuresJournal-ref: Appl. Phys. Lett. 116, 194001 (2020)Subjects: Quantum Physics (quant-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Superconductivity (cond-mat.supr-con)
We report on electron spin resonance spectroscopy measurements using a superconducting flux qubit with a sensing volume of 6 fl. The qubit is read out using a frequency-tunable Josephson bifurcation amplifier, which leads to an inferred measurement sensitivity of about 20 spins in a 1 s measurement. This sensitivity represents an order of magnitude improvement when compared with flux-qubit schemes using a dc-SQUID switching readout. Furthermore, noise spectroscopy reveals that the sensitivity is limited by flicker ($1/f$) flux noise.
- arXiv:2003.09132 [pdf, other]
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Title: Theoretical investigation of superconductivity in trilayer square-planar nickelatesComments: 16 pages, 7 figuresSubjects: Superconductivity (cond-mat.supr-con); Strongly Correlated Electrons (cond-mat.str-el)
The discovery of superconductivity in Sr-doped NdNiO$_{2}$ is a crucial breakthrough in the long pursuit for nickel oxide materials with electronic and magnetic properties similar to those of the cuprates. NdNiO$_2$ is the infinite-layer member of a family of square-planar nickelates with general chemical formula R$_{n+1}$Ni$_n$O$_{2n+2}$ (R = La, Pr, Nd, $n= 2, 3, ... \infty$). In this letter, we investigate superconductivity in the trilayer member of this series (R$_4$Ni$_3$O$_8$) using a combination of first-principles and $t-J$ model calculations. R$_4$Ni$_3$O$_8$ compounds resemble cuprates more than RNiO$_2$ materials in that only Ni-$d_{x^{2}-y^{2}}$ bands cross the Fermi level, they exhibit a largely reduced charge transfer energy, and as a consequence superexchange interactions are significantly enhanced. We find that the superconducting instability in doped R$_4$Ni$_3$O$_8$ compounds is considerably stronger with a maximum gap about four times larger than that in Sr$_{0.2}$Nd$_{0.8}$NiO$_2$.
- arXiv:2003.09143 [pdf, other]
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Title: The higher-order spectrum of simplicial complexes: a renormalization group approachComments: (39 pages,6 figures)Subjects: Disordered Systems and Neural Networks (cond-mat.dis-nn); Statistical Mechanics (cond-mat.stat-mech); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Lattice (hep-lat); Physics and Society (physics.soc-ph)
Network topology is a flourishing interdisciplinary subject that is relevant for different disciplines including quantum gravity and brain research. The discrete topological objects that are investigated in network topology are simplicial complexes. Simplicial complexes generalize networks by not only taking pairwise interactions into account, but also taking into account many-body interactions between more than two nodes. Higher-order Laplacians are topological operators that describe higher-order diffusion on simplicial complexes and constitute the natural mathematical objects that capture the interplay between network topology and dynamics. We show that higher-order up and down Laplacians can have a finite spectral dimension, characterizing the long time behaviour of the diffusion process on simplicial complexes that depends on their order $m$. We provide a renormalization group theory for the calculation of the higher-order spectral dimension of two deterministic models of simplicial complexes: the Apollonian and the pseudo-fractal simplicial complexes. We show that the RG flow is affected by the fixed point at zero mass, which determines the higher-order spectral dimension $d_S$ of the up-Laplacians of order $m$ with $m\geq 0$.
- arXiv:2003.09146 [pdf, other]
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Title: Grain boundary characteristics of Fe-based superconductorsComments: Invited reviewJournal-ref: Superconductor Science and Technology 33, 043001 (2020)Subjects: Superconductivity (cond-mat.supr-con)
Understanding the nature of grain boundary (GB) characteristics in combination with creating low-energy GBs by modifying the processing conditions, so-called GB engineering, is of great importance for controlling and reducing the defect density, leading to improved functionalities of polycrystalline metals and ceramics. For superconductors particularly, including both low- and high-temperature superconductors, GB engineering has been developed to improve especially the critical current densities, Jc, across these GBs. The intrinsic physical properties of a given superconductor such as the coherence length, the order parameter symmetry, and their anisotropies would determine the strategy of GB engineering. In this topical review, we present an overview of the GB characteristics and GB engineering of Fe-based superconductors (FBS) in the form of polycrystalline bulks and wires, and thin films with application potential, e.g. for high-field magnet wires. Prior to the FBS, GB engineering of the cuprates and MgB2 are also briefly covered.
- arXiv:2003.09157 [pdf, other]
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Title: Deterministic reversible model of non-equilibrium phase transitions and stochastic counterpartSubjects: Statistical Mechanics (cond-mat.stat-mech)
N point particles move within a billiard table made of two circular cavities connected by a straight channel. The usual billiard dynamics is modified so that it remains deterministic, phase space volumes preserving and time reversal invariant. Particles move in straight lines and are elastically reflected at the boundary of the table, as usual, but those in a channel that are moving away from a cavity invert their motion (rebound), if their number exceeds a given threshold T. When the geometrical parameters of the billiard table are fixed, this mechanism gives rise to non--equilibrium phase transitions in the large N limit: letting T/N decrease, the homogeneous particle distribution abruptly turns into a stationary inhomogeneous one. The equivalence with a modified Ehrenfest two urn model, motivated by the ergodicity of the billiard with no rebound, allows us to obtain analytical results that accurately describe the numerical billiard simulation results. Thus, a stochastic exactly solvable model that exhibits non-equilibrium phase transitions is also introduced.
- arXiv:2003.09160 [pdf, other]
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Title: Chiral Luttinger liquids in graphene tuned by irradiationComments: 12 pages, 5 figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We show that chiral co-propagating Luttinger liquids can be created and tuned by shining high frequency, circularly polarized light, normal to the layers, with different polarizations on two sections of bilayer graphene. By virtue of the broken time-reversal symmetry and the resulting mismatch of Chern number, the one-dimensional chiral modes are localized along the domain wall where the polarization changes. Single layer graphene hosts a single chiral edge mode near each Dirac node, whereas in bilayer graphene, there are two chiral modes near each of the Dirac nodes. These modes, under a high-frequency drive, essentially have a static charge distribution and form a chiral Luttinger liquid under Coulomb interaction, which can be tuned by means of the driving parameters. We also note that unlike the Luttinger liquids created by electrostatic confinement in bilayer graphene, here there is no back-scattering, and hence our wires along the node are stable to disorder.
- arXiv:2003.09165 [pdf, other]
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Title: Current cross-correlations and waiting time distributions in Andreev transport through Cooper pair splitters based on triple quantum dotsSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We study the spin-resolved subgap transport in a triple quantum-dot system coupled to one superconducting and two ferromagnetic leads. We examine the Andreev processes in the parallel and antiparallel alignments of ferromagnets magnetic moments in both the linear and nonlinear response regimes. The emphasis is put on the analysis of the current cross-correlations between the currents flowing through the left and right arms of the device and relevant electron waiting time distributions. We show that both quantities can give an important insight into the subgap transport processes and their analysis can help optimizing the system parameters for achieving the considerable Andreev current and efficient Cooper pair splitting. Strong positive values of cross-correlations are associated with the presence of tunneling processes enhancing the Cooper pair splitting efficiency, while short waiting times for electrons tunneling through distinct ferromagnetic contacts indicate fast splitting of emitted Cooper pairs. In particular, we study two detuning schemes and show that antisymmetric shift of side quantum dots energy levels is favorable for efficient Cooper pair splitting. The analysis of spin-resolved waiting time distributions supports the performance enhancement due to the presence of ferromagnetic contacts, which is in particular revealed for short times. Finally, we consider the effect of changing the inter-dot hopping amplitude and predict that strong inter-dot correlations lead to a reduction of Andreev transport properties in low-bias limit.
- arXiv:2003.09185 [pdf, other]
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Title: Cutting and slicing weak solidsSubjects: Soft Condensed Matter (cond-mat.soft); Fluid Dynamics (physics.flu-dyn)
Dicing soft solids with a sharp knife is quicker and smoother if the blade is sliding rapidly parallel to its edge in addition to the normal squeezing motion. We explain this common observation with a consistent theory suited for soft gels and departing from the standard theories of elastic fracture mechanics developed for a century. The gel is assumed to locally fails when submitted to stresses exceeding a threshold $\sigma_1$. The changes in its structure generate a liquid layer coating the blade and transmitting the stress through viscous forces. The driving parameters are the ratio $U/W$ of the normal to the tangential velocity of the blade, and the characteristic length $\eta W/\sigma_1$, with $\eta$ the viscosity of the liquid. The existence of a maximal value of $U/W$ for a steady regime explains the crucial role of the tangential velocity for slicing biological and other soft materials.
- arXiv:2003.09189 [pdf, other]
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Title: Emergence of a ferromagnetic insulating state in LaMnO$_3$/SrTiO$_3$ heterostructures: The role of strong electronic correlations and strainSubjects: Strongly Correlated Electrons (cond-mat.str-el)
Inspired by the experimental findings of an exotic ferromagnetic insulating state in LaMnO$_3$/SrTiO$_3$ heterostructures, we calculate the electronic and magnetic state of LaMnO$_3$/SrTiO$_3$ superlattices with comparable thicknesses employing ab-initio dynamical mean-field theory. Projecting on the low-energy subspace of Mn $3d$ and Ti $3d$ states, and solving a multi-impurity problem, our approach emphasizes on local correlations at Mn and Ti sites. We find that a ferromagnetic insulating state emerges due to intrinsic effects of strong correlations in the system, in agreement with experimental studies. We also predict that, due to electronic correlations, the emerging 2D electron gas is located at the LMO side of the interface. This is in contrast to DFT results that locate the electron gas on the STO side. We estimate the transition temperature for the paramagnetic to ferromagnetic phase transition, which may be verified experimentally. Importantly, we also clarify that the epitaxial strain is a key ingredient for the emergence of the exotic ferromagnetic insulating state. This becomes clear from calculations on a strained LaMnO$_3$ system, also showing ferromagnetism which is not seen in the unstrained bulk material.
- arXiv:2003.09190 [pdf, ps, other]
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Title: Paramagnetic Meissner, vortex and 'onion' ground states in Fulde-Ferrell finite-size superconductorComments: 9 pages, 8 figuresJournal-ref: Phys. Rev. B 101, 184513 (2020)Subjects: Superconductivity (cond-mat.supr-con); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We theoretically find that finite size Fulde-Ferrell (FF) superconductor (which is characterized by spatially nonuniform ground state $\Psi \sim \text{exp}(-i{\bf q}_{FF}{\bf r})$ and $|\Psi|(r)=const$ in the bulk case, where $\Psi$ is a superconducting order parameter) has paramagnetic Meissner, vortex and 'onion' ground states with $|\Psi|(r) \neq const$. These states are realized due to boundary effect when the lateral size of superconductor $L \sim 1/q_{FF}$. We argue, that predicted states could be observed in thin disk/square made of superconductor-ferromagnet-normal metal trilayer with $L \simeq 150-600 nm$.
- arXiv:2003.09193 [pdf, other]
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Title: Optimal estimates of diffusion coefficients from molecular dynamics simulationsComments: 15 pages, 6 figures. The following article has been submitted to The Journal of Chemical PhysicsSubjects: Computational Physics (physics.comp-ph); Statistical Mechanics (cond-mat.stat-mech); Biological Physics (physics.bio-ph)
Translational diffusion coefficients are routinely estimated from molecular dynamics simulations. Linear fits to mean squared displacement (MSD) curves have become the de facto standard, from simple liquids to complex biomacromolecules. Nonlinearities in MSD curves at short times are handled with a wide variety of ad hoc practices, such as partial and piece-wise fitting of the data. Here, we present a rigorous framework to obtain reliable estimates of the diffusion coefficient and its statistical uncertainty. We also assess in a quantitative manner if the observed dynamics is indeed diffusive. By accounting for correlations between MSD values at different times, we reduce the statistical uncertainty of the estimator and thereby increase its efficiency. With a Kolmogorov-Smirnov test, we check for possible anomalous diffusion. We provide an easy-to-use Python data analysis script for the estimation of diffusion coefficients. As an illustration, we apply the formalism to molecular dynamics simulation data of pure TIP4P-D water and a single ubiquitin protein. In a companion paper [J. Chem. Phys. XXX, YYYYY (2020)], we demonstrate its ability to recognize deviations from regular diffusion caused by systematic errors in a common trajectory "unwrapping" scheme that is implemented in popular simulation and visualization software.
- arXiv:2003.09205 [pdf, other]
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Title: Systematic errors in diffusion coefficients from long-time molecular dynamics simulations at constant pressureComments: 6 pages, 5 figures. The following article has been accepted for publication at The Journal of Chemical PhysicsSubjects: Computational Physics (physics.comp-ph); Statistical Mechanics (cond-mat.stat-mech); Biological Physics (physics.bio-ph)
In molecular dynamics simulations under periodic boundary conditions, particle positions are typically wrapped into a reference box. For diffusion coefficient calculations using the Einstein relation, the particle positions need to be unwrapped. Here, we show that a widely used heuristic unwrapping scheme is not suitable for long simulations at constant pressure. Improper accounting for box-volume fluctuations creates, at long times, unphysical trajectories and, in turn, grossly exaggerated diffusion coefficients. We propose an alternative unwrapping scheme that resolves this issue. At each time step, we add the minimal displacement vector according to periodic boundary conditions for the instantaneous box geometry. Here and in a companion paper [J. Chem. Phys. XXX, YYYYY (2020)], we apply the new unwrapping scheme to extensive molecular dynamics and Brownian dynamics simulation data. We provide practitioners with a formula to assess if and by how much earlier results might have been affected by the widely used heuristic unwrapping scheme.
- arXiv:2003.09214 [pdf]
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Title: Phase-resolved Detection and Control of Ultrabroadband THz Pulses coupled to a Scanning Tunneling Microscope JunctionComments: 5 figures, supporting information availableSubjects: Applied Physics (physics.app-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Coupling phase-stable single-cycle terahertz (THz) pulses to scanning tunneling microscope (STM) junctions enables spatio-temporal imaging with femtosecond temporal and \r{A}ngstrom spatial resolution. The time resolution achieved in such THz-gated STM is ultimately limited by the sub-cycle temporal variation of the tip-enhanced THz field acting as an ultrafast voltage pulse, and hence by the ability to feed high-frequency, broadband THz pulses into the junction. Here, we report on the coupling of ultrabroadband (1-30 THz) single-cycle THz pulses from a spintronic THz emitter (STE) into a metallic STM junction. We demonstrate broadband phase resolved detection of the tip-enhanced THz waveform via THz-field-induced modulation of ultrafast photocurrents across the junction. Comparison to the unperturbed far-field THz waveform reveals the antenna response of the STM tip. Despite tip-induced low-pass filtering, frequencies up to 15 THz can be detected in the enhanced near-field, resulting in THz transients with a half-cycle period of 115 fs. We further demonstrate versatile phase and polarity control of the THz waveform depending on the STE excitation conditions and magnetization, and show that up to 2 Volts THz bias at 1 MHz repetition rate can be achieved in the current setup. Finally, we find a nearly constant THz voltage and waveform over a wide range of tip-sample distances, which by comparison to numerical simulations confirms the quasi-static nature of the THz pulses. Our results demonstrate the suitability of spintronic THz emitters for ultrafast THz-STM and provide insight into the femtosecond response of defined nanoscale junctions.
- arXiv:2003.09217 [pdf, other]
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Title: Effect of cytosol viscosity on the flow behavior of red blood cell suspensions in microvesselsComments: 16 pages, 13 figures, 4 tablesSubjects: Soft Condensed Matter (cond-mat.soft); Biological Physics (physics.bio-ph); Fluid Dynamics (physics.flu-dyn)
The flow behavior of blood in microvessels is directly associated with tissue perfusion and oxygen delivery. Current efforts on modeling blood flow have primarily focused on the flow properties of blood with red blood cells (RBCs) having a viscosity ratio $C$ of unity between the cytosol and suspending medium, while under physiological conditions the cytosol viscosity is about five times larger than the plasma viscosity (i.e., $C\approx 5$). The importance of $C$ for the behavior of single RBCs in fluid flow has already been demonstrated, while the effect of $C$ on blood flow has only been sparsely studied. We employ mesoscopic hydrodynamic simulations to perform a systematic investigation of flow properties of RBC suspensions with different cytosol viscosities for various flow conditions in cylindrical microchannels. Our main aim is to link macroscopic flow properties such as flow resistance to single cell deformation and dynamics as a function of $C$. Starting from a dispersed cell configuration, we find that the flow convergence and the development of a RBC-free layer (RBC-FL) depend only weakly on $C$, and require a convergence length in the range of $25D-50D$, where $D$ is the channel diameter. The flow resistance for $C=5$ is nearly the same as that for $C=1$, which is facilitated by a slightly larger RBC-FL thickness for $C=5$. This effect is due to the suppression of membrane motion and dynamic shape deformations by a more viscous cytosol for $C=5$, resulting in a more compact cellular core of the flow in comparison to $C=1$. The weak effect of cytosol viscosity on the flow resistance and RBC-FL explains why cells can have a high concentration of hemoglobin for efficient oxygen delivery, without a pronounced increase in the flow resistance.
- arXiv:2003.09222 [pdf, other]
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Title: Stability of topological wall defects on spheres with n-atic orderComments: 8 pages, 5 figuresJournal-ref: Phys. Rev. Research 2, 023215 (2020)Subjects: Soft Condensed Matter (cond-mat.soft)
Topological point defects on orientationally ordered spheres, and on deformable fluid vesicles have been partly motivated by their potential applications in creating super-atoms with directional bonds through functionalization of the "bald-spots" created by topological point defects, thus paving the way for atomic chemistry at micron scales. We show that singular wall defects, topologically unstable "bald lines" in two dimensions, are stabilized near the order-disorder transition on a sphere. We attribute their stability to free-energetic considerations, which override those of topological stability.
- arXiv:2003.09226 [pdf, other]
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Title: Critical properties of the valence-bond-solid transition in lattice quantum electrodynamicsComments: 16 pages, 6 figures, 8 tables; v2: published versionJournal-ref: Phys. Rev. D 101, 094505 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el); High Energy Physics - Lattice (hep-lat); High Energy Physics - Theory (hep-th)
Elucidating the phase diagram of lattice gauge theories with fermionic matter in 2+1 dimensions has become a problem of considerable interest in recent years, motivated by physical problems ranging from chiral symmetry breaking in high-energy physics to fractionalized phases of strongly correlated materials in condensed matter physics. For a sufficiently large number $N_f$ of flavors of four-component Dirac fermions, recent sign-problem-free quantum Monte Carlo studies of lattice quantum electrodynamics (QED$_3$) on the square lattice have found evidence for a continuous quantum phase transition between a power-law correlated conformal QED$_3$ phase and a confining valence-bond-solid phase with spontaneously broken point-group symmetries. The critical continuum theory of this transition was shown to be the $O(2)$ QED$_3$-Gross-Neveu model, equivalent to the gauged Nambu-Jona-Lasinio model, and critical exponents were computed to first order in the large-$N_f$ expansion and the $\epsilon$ expansion. We extend these studies by computing critical exponents to second order in the large-$N_f$ expansion and to four-loop order in the $\epsilon$ expansion below four spacetime dimensions. In the latter context, we also explicitly demonstrate that the discrete $\mathbb{Z}_4$ symmetry of the valence-bond-solid order parameter is dynamically enlarged to a continuous $O(2)$ symmetry at criticality for all values of $N_f$.
- arXiv:2003.09243 [pdf, other]
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Title: Flat band superconductivity in the square-octagon latticeComments: 8 pages, 4 figuresSubjects: Superconductivity (cond-mat.supr-con); Strongly Correlated Electrons (cond-mat.str-el)
The discovery of superconductivity in twisted bilayer graphene has triggered a resurgence of interest in flat-band superconductivity. Here, we investigate the square-octagon lattice, which also exhibits two perfectly flat bands when next-nearest neighbour hopping or an external magnetic field are added to the system. We calculate the superconducting phase diagram in the presence of on-site attractive interactions and find two superconducting domes, as observed in several types of unconventional superconductors. The critical temperature shows a linear dependence on the coupling constant, suggesting that superconductivity might reach high temperatures in the square-octagon lattice. Our model could be experimentally realized using photonic or ultracold atoms lattices.
- arXiv:2003.09258 [pdf, ps, other]
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Title: Statistical description of interacting quantum systems in equilibrium statesAuthors: Wen-ge WangComments: 13 pages, no figureSubjects: Quantum Physics (quant-ph); Statistical Mechanics (cond-mat.stat-mech)
We study the statistical description of a small quantum system that interacts in a generic way with a large quantum environment, when the total system lies in an equilibrium state described by a microcanonical ensemble. The focus is on the difference between the reduced density matrix (RDM) of the central system in this interacting case and the RDM obtained in the uncoupled case. In the eigenbasis of the central system's Hamiltonian, it is shown that the difference between diagonal elements is mainly confined by the ratio of the maximum width of the eigenfunctions of the total system in the uncoupled basis to the width of the microcanonical energy shell; meanwhile, the difference between offdiagonal elements is given by the ratio of certain property of the interaction Hamiltonian to the related level spacing of the central system. As an application, a condition is given under which the RDM has a canonical Gibbs form that includes certain averaged effect of the interaction. It is argued that, for a central system that interacts locally with a many-body quantum chaotic system, it is quite possible for the RDM to have a Gibbs form. We also study the RDM which is computed from a typical state of the total system within an energy shell.
- arXiv:2003.09263 [pdf, ps, other]
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Title: Suppressing convection strength using confinement during protein crystallizationSubjects: Soft Condensed Matter (cond-mat.soft); Fluid Dynamics (physics.flu-dyn)
Fluid convection during protein crystallization plays a significant role in determining crystal growth rate and crystal quality. Crystals grown in reduced flow strength gives better quality crystal. Hence, tuning the flow strength is very essential in the crystal growth process. In this work, we have demonstrated a new method to suppress the flow strength using confinement effect during vapor diffusion method of protein crystallization where the crystal is grown inside an evaporating droplet. Flow study is carried out at four different confinement conditions to study the effect of confinement. Flow inside the droplet is caused by evaporation induced natural convection which is measured by micro-PIV method. Also concentration gradient generated around the growing crystal also induces buoyancy driven flow around the protein crystal during the crystal growth phase. The evaporation rate from the droplet and the flow strength inside the droplet get suppressed by increasing confinement. Hence, the flow strength can be tuned by adjusting the confinement which is a very simple method to tune the flow strength.
- arXiv:2003.09270 [pdf, other]
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Title: Trapping, gliding, vaulting: Transport of semiflexible polymers in periodic post arraysComments: 14 pages, 12 figuresSubjects: Soft Condensed Matter (cond-mat.soft); Fluid Dynamics (physics.flu-dyn)
The transport of deformable particles through porous media underlies a wealth of applications ranging from filtration to oil recovery to the transport and spreading of biological agents. Using direct numerical simulations, we analyze the dynamics of semiflexible polymers under the influence of an imposed flow in a structured two-dimensional lattice serving as an idealization of a porous medium. This problem has received much attention in the limit of reptation and for long-chain polymer molecules such as DNA that are transported through micropost arrays for electrophoretic chromatographic separation. In contrast to long entropic molecules, the dynamics of elastic polymers results from a combination of scattering with the obstacles and flow-induced buckling instabilities. We identify three dominant modes of transport that involve trapping, gliding and vaulting of the polymers around the obstacles, and we reveal their essential features using tools from dynamical systems theory. The interplay of these scattering dynamics with transport and deformations in the imposed flow results in the long-time asymptotic dispersion of the center of mass, which we quantify in terms of a hydrodynamic dispersion tensor. We then discuss a simple yet efficient chromatographic device that exploits the competition between different modes of transport to sort filaments in a dilute suspension according to their lengths.
- arXiv:2003.09274 [pdf, other]
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Title: The range of non-Kitaev terms and fractional particles in RuCl$_3$Authors: Yiping Wang, Gavin B. Osterhoudt, Yao Tian, Paige Lampen-Kelley, Arnab Banerjee, Thomas Goldstein, Jun Yan, Johannes Knolle, Huiwen Ji, Robert J. Cava, Joji Nasu, Yukitoshi Motome, Stephen E. Nagler, David Mandrus, Kenneth S. BurchJournal-ref: npj Quantum Materials (2020) 5:14Subjects: Strongly Correlated Electrons (cond-mat.str-el); Materials Science (cond-mat.mtrl-sci)
Significant efforts have focused on the magnetic excitations of relativistic Mott insulators, predicted to realize the Kitaev quantum spin liquid (QSL). This exactly solvable model involves a highly entangled state resulting from bond-dependent Ising interactions that produce excitations which are non-local in terms of spin flips. A key challenge in real materials is identifying the relative size of the non-Kitaev terms and their role in the emergence or suppression of fractional excitations. Here, we identify the energy and temperature boundaries of non-Kitaev interactions by direct comparison of the Raman susceptibility of RuCl3 with quantum Monte Carlo (QMC) results for the Kitaev QSLs. Moreover, we further confirm the fractional nature of the magnetic excitations, which is given by creating a pair of fermionic quasiparticles. Interestingly, this fermionic response remains valid in the non-Kitaev range. Our results and focus on the use of the Raman susceptibility provide a stringent new test for future theoretical and experimental studies of QSLs.
- arXiv:2003.09275 [pdf, other]
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Title: BetheSF: Efficient computation of the exact tagged particle propagator in single file systems via the Bethe eigenspectrumComments: The code is available upon requestSubjects: Computational Physics (physics.comp-ph); Statistical Mechanics (cond-mat.stat-mech); Computational Engineering, Finance, and Science (cs.CE)
Single file diffusion is a paradigm for strongly correlated classical stochastic many-body dynamics and has widespread applications in soft condensed matter and biophysics. However, exact results for single file systems are sparse and limited to the simplest scenarios. We present an algorithm for computing the non-Markovian time-dependent conditional probability density function of a tagged particle in a single file of $N$ particles diffusing in a confining external potential. The algorithm implements an eigenexpansion of the full interacting many-body problem obtained by means of the Coordinate Bethe Ansatz. While formally exact, the Bethe eigenspectrum involves the generation and evaluation of permutations, which becomes unfeasible already for moderate particle numbers $N$. Here we exploit the underlying symmetries of the system and show that it is possible to reduce the complexity of the algorithm from the worst case scenario $\mathcal{O}(N!)$ to up to $\mathcal{O}(N)$. A C++ code to calculate the non-Markovian probability density function using this algorithm is provided. Solutions for simple model potentials are readily implemented incl. single file in a flat and a 'tilted' box, as well as in a parabolic potential. Notably, the program allows for implementations of solutions in arbitrary external potentials under the condition that the user can supply solutions to the respective eigenspectra.
- arXiv:2003.09277 [pdf, other]
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Title: Interaction-induced topological states of photon pairsComments: 11 pages, 4 figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Optics (physics.optics)
To date, the concept of topological order relies heavily on the properties of single-particle bands. Only recently it has been realized that interactions can have a dramatic impact on topological properties not only modifying the topology of the bands but also creating a topological order in an otherwise trivial system. Applying an extended version of the Bose-Hubbard model, we investigate a system which, being topologically trivial in the single-particle regime, harbors topologically nontrivial edge and interface states of repulsively bound photon pairs. Whereas binding of the photons in this model is captured by a standard local interaction term, an additional direct two-photon hopping renders the system topologically non-trivial. Besides their interaction-induced origin, predicted two-photon edge states exhibit a range of other unexpected features, including the robustness to collapse of the corresponding bulk band and the ability to coexist with the continuum of two-photon scattering states forming a bound state in the continuum. Performing rigorous calculation of the Zak phase for bound photon pairs, we prove the topological origin of the two-photon edge states.
- arXiv:2003.09278 [pdf]
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Title: Designer Bloch Plasmon Polariton Dispersion in Hyperbolic Meta-GratingsAuthors: Nicolò Maccaferri, Tommi Isoniemi, Michael Hinczewski, Marzia Iarossi, Giuseppe Strangi, Francesco De AngelisSubjects: Optics (physics.optics); Materials Science (cond-mat.mtrl-sci)
Hyperbolic metamaterials (HMMs) represent a novel class of fascinating anisotropic plasmonic materials, supporting highly confined propagating plasmon polaritons in addition to surface plasmon polaritons. However, it is very challenging to tailor and excite these modes at optical frequencies by prism coupling because of the intrinsic difficulties in engineering non-traditional optical properties with artificial nanostructures and the unavailability of high refractive index prisms for matching the momentum between the incident light and the guided modes. Here, we report the mechanism of excitation of high-k Bloch-like Plasmon Polariton (BPPs) modes with ultrasmall modal volume using a meta-grating, which is a combined structure of a metallic diffraction grating and a type II HMM. We show how a 1D plasmonic grating without any mode in the infrared spectral range, if coupled to a HMM supporting high-k modes, can efficiently enable the excitation of these modes via coupling to far-field radiation. Our theoretical predictions are confirmed by reflection measurements as a function of angle of incidence and excitation wavelength. We introduce design principles to achieve a full control of high-k modes in meta-gratings, thus enabling a better understanding of light-matter interaction in this type of hybrid meta-structures. The proposed spectral response engineering is expected to find potential applications in bio-chemical sensors, integrated optics and optical sub-wavelength imaging.
- arXiv:2003.09296 [pdf, other]
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Title: Chaotic dynamics of graphene and graphene nanoribbonsAuthors: Malcolm Hillebrand, Bertin Many Manda, George Kalosakas, Enrico Gerlach, Charalampos SkokosComments: 18 pages, 5 figuresSubjects: Chaotic Dynamics (nlin.CD); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Applied Physics (physics.app-ph)
We study the chaotic dynamics of graphene structures, considering both a periodic, defect free, graphene sheet and graphene nanoribbons (GNRs) of various widths. By numerically calculating the maximum Lyapunov exponent, we quantify the chaoticity for a spectrum of energies in both systems. We find that for all cases, the chaotic strength increases with the energy density. For the GNRs, we also investigate the impact of the width and chirality (armchair or zigzag edges) on their chaotic behavior. Our results suggest that due to the free edges the chaoticity of GNRs is stronger than the periodic graphene sheet, and decreases by increasing width, tending asymptotically to the bulk value. In addition, the chaotic strength of armchair GNRs is higher than a zigzag ribbon of the same width. Further, we show that the composition of ${}^{12}C$ and ${}^{13}C$ carbon isotopes in graphene has a minor impact on its chaotic strength.
- arXiv:2003.09308 [pdf, other]
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Title: Neutron Diffraction Evidence for Local Spin Canting, Weak Jahn-Teller Distortion, and Magnetic Compensation in Ti$_{1-x}$Mn$_{x}$Co$_2$O$_4$ SpinelAuthors: P. Pramanik, D. C. Joshi, M. Reehuis, A. Hoser, J. U. Hoffmann, R. S. Manna, T. Sarkar, S. ThotaComments: 19 pages, 15 figuresJournal-ref: J. Phys.: Condens. Matter 32, 245801 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el); Materials Science (cond-mat.mtrl-sci)
A systematic study using neutron diffraction and magnetic susceptibility are reported on Mn substituted ferrimagnetic inverse spinel Ti$_{1-x}$Mn$_{x}$Co$_2$O$_4$ in the temperature interval 1.6 K $\leq$ $T$ $\leq$ 300 K. Our neutron diffraction study reveals cooperative distortions of the $T$O$_6$ octahedral for all the Jahn-Teller active ions $T$ = Mn$^{3+}$, Ti$^{3+}$ and Co$^{3+}$, which are confirmed by the X-ray photoelectron spectroscopy. Two specific compositions ($x$ = 0.2 and 0.4) have been chosen because of their unique features: noncollinear Yafet-Kittel type ordering, and weak tetragonal distortion with ${c/a}$ $<$ 1, in which the apical bond length $d_c$($T_B$-O) is longer than the equatorial $d_{ab}$($T_B$-O) due to the splitting of the $e_g$ level of Mn$^{3+}$ ions into $d_{x^2-y^2}$ and $d_{z^2}$. For $x$ = 0.4, the distortion in the $T_B$O$_6$ octahedra is stronger as compared to $x$ = 0.2 because of the higher content of trivalent Mn. Ferrimagnetic ordering in $x$ = 0.4 and $x$ = 0.2 sets in at 110.3 and 78.2 K, respectively due to the unequal magnetic moments of cations, where Ti$^{3+}$, Mn$^{3+}$, and Co$^{3+}$ occupying the octahedral, whereas, Co$^{2+}$ sits in the tetrahedral site. In addition, weak antiferromagnetic component could be observed lying perpendicular to the ferrimagnetic component. The analysis of static and dynamic magnetic susceptibilities combined with the heat-capacity data reveals a magnetic compensation phenomenon at $T_{COMP}$ = 25.4 K in $x$ = 0.2 and a reentrant spin-glass behaviour in $x$ = 0.4 with a freezing temperature $\sim$110.1 K. The compensation phenomenon is characterized by sign reversal of magnetization and bipolar exchange bias effect below $T_{COMP}$ with its magnitude depending on the direction of external magnetic field and the cooling protocol.
- arXiv:2003.09309 [pdf]
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Title: Drying of porous media by concurrent drainage and evaporation: A pore network modeling studySubjects: Soft Condensed Matter (cond-mat.soft)
Drainage and evaporation can occur simultaneously during the drying of porous media, but the interactions between these processes and their effects on drying are rarely studied. In this work, we develop a pore network model that considers drainage, evaporation, and rarefied multi-component gas transport in porous media with nanoscale pores. Using this model, we investigate the drying of a liquid solvent-saturated porous medium enabled by the flow of purge gas through it. Simulations show that drying progresses in three stages, and the solvent removal by drainage effects (evaporation effects) becomes increasingly weak (strong) as drying progresses through these stages. Interestingly, drainage can contribute considerably to solvent removal even after evaporation effects become very strong, especially when the applied pressure difference across the porous medium is low. We show that these phenomena are the results of the coupling between the drainage and evaporation effects and this coupling depends on the operating conditions and the stage of drying.
- arXiv:2003.09351 [pdf, ps, other]
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Title: Chaotic diffusion for particles moving in a time dependent potential wellSubjects: Statistical Mechanics (cond-mat.stat-mech); Chaotic Dynamics (nlin.CD)
The chaotic diffusion for particles moving in a time dependent potential well is described by using two different procedures: (i) via direct evolution of the mapping describing the dynamics and ; (ii) by the solution of the diffusion equation. The dynamic of the diffusing particles is made by the use of a two dimensional, nonlinear area preserving map for the variables energy and time. The phase space of the system is mixed containing both chaos, periodic regions and invariant spanning curves limiting the diffusion of the chaotic particles. The chaotic evolution for an ensemble of particles is treated as random particles motion and hence described by the diffusion equation. The boundary conditions impose that the particles can not cross the invariant spanning curves, serving as upper boundary for the diffusion, nor the lowest energy domain that is the energy the particles escape from the time moving potential well. The diffusion coefficient is determined via the equation of the mapping while the analytical solution of the diffusion equation gives the probability to find a given particle with a certain energy at a specific time. The momenta of the probability describe qualitatively the behavior of the average energy obtained by numerical simulation, which is investigated either as a function of the time as well as some of the control parameters of the problem.
- arXiv:2003.09360 [pdf]
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Title: Efficient Modelling of Ion Structure and Dynamics in Inorganic Metal Halide PerovskitesAuthors: Salvador Rodriguez-Gomez Balestra, Jose Manuel Vicent-Luna, Sofia Calero, Shuxia Tao, Juan A. AntaSubjects: Materials Science (cond-mat.mtrl-sci)
Metal halide perovskites (MHPs) are nowadays one of the most studied semiconductors due to their exceptional performance as active layers in solar cells. Although MHPs are excellent solid-state semiconductors, they are also ionic compounds, where ion migration plays a decisive role in their formation, their photovoltaic performance and their long-term stability. Given the above-mentioned complexity, molecular dynamics simulations based on classical force fields are especially suited to study MHP properties, such as lattice dynamics and ion migration. In particular, the possibility to model mixed compositions is important since they are the most relevant to optimize the optical band gap and the stability. With this intention, we employ DFT calculations and a genetic algorithm to develop a fully transferable classical force field valid for the benchmark inorganic perovskite compositional set CsPb(Br_xI_(1-x))_3 (x = 0,1/3,2/3,1). The resulting force field reproduces correctly, with a common set of parameters valid for all compositions, the experimental lattice parameter as a function of bromide/iodide ratio, the ion-ion distances and the XRD spectra of the pure and mixed structures. The simulated thermal conductivities and ion migration activation energies of the pure compounds are also in good agreement with experimental trends. Our molecular dynamics simulations make it possible to predict the compositional dependence of the ionic diffusion coefficient on bromide/iodide ratio and vacancy concentration. For vacancy concentrations of around 9 10^21 cm^-3, we obtained ionic diffusion coefficients at ambient temperature of 10^-11 and 10^-13 cm2/s for CsPbBr3 and CsPbI3, respectively. Interestingly, in comparison with the pure compounds, we predict a significantly lower activation energy for vacancy migration and faster diffusion for the mixed perovskites.
- arXiv:2003.09414 [pdf, other]
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Title: Polaritonic XY-Ising MachineComments: 23 pages, 3 figures, invited submissionSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Emerging Technologies (cs.ET); Optics (physics.optics)
Gain-dissipative systems of various physical origin have recently shown the ability to act as analogue minimisers of hard combinatorial optimisation problems. Whether or not these proposals will lead to any advantage in performance over the classical computations depends on the ability to establish controllable couplings for sufficiently dense short- and long-range interactions between the spins. Here, we propose a polaritonic XY-Ising machine based on a network of geometrically isolated polariton condensates capable of minimising discrete and continuous spin Hamiltonians. We elucidate the performance of the proposed computing platform for two types of couplings: relative and absolute. The interactions between the network nodes might be controlled by redirecting the emission between the condensates or by sending the phase information between nodes using resonant excitation. We discuss the conditions under which the proposed machine leads to a pure polariton simulator with pre-programmed couplings or results in a hybrid classical polariton simulator. We argue that the proposed architecture for the remote coupling control offers an improvement over geometrically coupled condensates in both accuracy and stability as well as increases versatility, range and connectivity of spin Hamiltonians that can be simulated with polariton networks.
Replacements
- arXiv:1711.03459 (replaced) [pdf, other]
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Title: Extreme matrices or how an exponential map links classical and free extreme lawsComments: 18 pages, 4 figure; replaced version with new resultsSubjects: Mathematical Physics (math-ph); Statistical Mechanics (cond-mat.stat-mech); Probability (math.PR); Statistics Theory (math.ST)
Using the proposed by us thinning approach to describe extreme matrices, we find an explicit exponentiation formula linking classical extreme laws of Fr\'echet, Gumbel and Weibull given by Fisher-Tippet-Gnedenko classification and free extreme laws of free Fr\'echet, free Gumbel and free Weibull by Ben Arous and Voiculescu [1]. We also develop an extreme random matrix formalism, in which refined questions about extreme matrices can be answered. In particular, we demonstrate explicit calculations for several more or less known random matrix ensembles, providing examples of all three free extreme laws. Finally, we present an exact mapping, showing the equivalence of free extreme laws to the Peak-Over-Threshold method in classical probability.
- arXiv:1810.08222 (replaced) [pdf]
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Title: Visualization of multifractal superconductivity in a two-dimensional transition metal dichalcogenide in the weak-disorder regimeAuthors: Carmen Rubio-Verdú, Antonio M. García-García, Hyejin Ryu, Deung-Jang Choi, Javier Zaldívar, Shujie Tang, Bo Fan, Zhi-Xun Shen, Sung-Kwan Mo, José Ignacio Pascual, Miguel M. UgedaSubjects: Superconductivity (cond-mat.supr-con)
Eigenstate multifractality is a distinctive feature of non-interacting disordered metals close to a metal-insulator transition, whose properties are expected to extend to superconductivity. While multifractality in three dimensions (3D) only develops near the critical point for specific strong-disorder strengths, multifractality in 2D systems is expected to be observable even for weak disorder. Here we provide evidence for multifractal features in the superconducting state of an intrinsic weakly disordered single-layer NbSe$_2$ by means of low-temperature scanning tunneling microscopy/spectroscopy. The superconducting gap, characterized by its width, depth and coherence peaks' amplitude, shows a characteristic spatial modulation coincident with the periodicity of the quasiparticle interference pattern. Spatial inhomogeneity of the superconducting gap width, proportional to the local order parameter in the weak-disorder regime, follows a log-normal statistical distribution as well as a power-law decay of the two-point correlation function, in agreement with our theoretical model. Furthermore, the experimental singularity spectrum f($\alpha$) shows anomalous scaling behavior typical from 2D weakly disordered systems.
- arXiv:1812.06463 (replaced) [pdf, other]
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Title: Strategy for accurate thermal biasing at the nanoscaleAuthors: Artem Denisov, Evgeny Tikhonov, Stanislau Piatrusha, Ivan Khrapach, Francesco Rossella, Mirko Rocci, Lucia Sorba, Stefano Roddaro, Vadim KhrapaiComments: revised version of a submitted manuscriptJournal-ref: Nanotechnology 31, 324004 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We analyze the benefits and shortcomings of a thermal control in nanoscale electronic conductors by means of the contact heating scheme. Ideally, this straightforward approach allows one to apply a known thermal bias across nanostructures directly through metallic leads, avoiding conventional substrate intermediation. We show, by using the average noise thermometry and local noise sensing technique in InAs nanowire based devices, that a nanoscale metallic constriction on a SiO2 substrate acts like a diffusive conductor with negligible electron-phonon relaxation and non-ideal leads. The non-universal impact of the leads on the achieved thermal bias -- which depends on their dimensions, shape and material composition -- is hard to minimize, but is possible to accurately calibrate in a properly designed nano-device. Our results allow to reduce the issue of the thermal bias calibration to the knowledge of the heater resistance and pave the way for accurate thermoelectric or similar measurements at the nanoscale.
- arXiv:1902.04759 (replaced) [pdf, ps, other]
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Title: Scaling laws for frictional granular materials confined by constant pressure under oscillatory shearComments: 13 pages, 18 figuresJournal-ref: Phys. Rev. E 101, 042902 (2020)Subjects: Soft Condensed Matter (cond-mat.soft)
Herein, we numerically study the rheology of a two-dimensional frictional granular system confined by constant pressure under oscillatory shear. Several scaling laws for the storage and loss moduli against the scaled strain amplitude have been found. The scaling laws in plastic regime for large strain amplitude can be understood by the angular distributions of the contact force. The scaling exponents are estimated by considering the physical mechanism.
- arXiv:1903.00463 (replaced) [pdf, other]
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Title: Topological braiding of non-Abelian mid-gap defects in classical meta-materialsJournal-ref: Phys. Rev. Lett. 124, 146801 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci)
Non-trivial braid-group representations appear as non-Abelian quantum statistics of emergent Majorana zero modes in one and two-dimensional topological superconductors. Here, we generate such representations with topologically protected domain-wall modes in a classical analogue of the Kitaev superconducting chain, with a particle-hole like symmetry and a Z2 topological invariant. The mid-gap modes are found to exhibit distinct fusion channels and rich non-Abelian braiding properties, which are investigated using a T-junction setup. We employ the adiabatic theorem to explicitly calculate the braiding matrices for one and two pairs of these mid-gap topological defects.
- arXiv:1905.12373 (replaced) [pdf, other]
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Title: Ultrafast Control of Excitonic Rashba Fine Structure by Phonon Coherences in a Metal Halide Perovskite CH$_3$NH$_3$PbI$_3$Authors: Z. Liu, C. Vaswani, X. Yang, X. Zhao, Y. Yao, Z. Song, D. Cheng, Y. Shi, L. Luo, D. H. Mudiyanselage, C. Huang, J.-M. Park, R.H.J. Kim, J. Zhao, Y. Yan, K.-M. Ho, J. WangComments: Phys. Rev. Lett, in press (2020)Journal-ref: Phys. Rev. Lett. 124, 157401 (2020)Subjects: Materials Science (cond-mat.mtrl-sci); Strongly Correlated Electrons (cond-mat.str-el); Quantum Physics (quant-ph)
We discover hidden Rashba fine structure in CH$_3$NH$_3$PbI$_3$ and demonstrate its quantum control by vibrational coherence through symmetry-selective vibronic (electron-phonon) coupling. Above a critical threshold of a single-cycle terahertz pump field, a Raman phonon mode distinctly modulates the middle excitonic states with {\em persistent} coherence for more than ten times longer than the ones on two sides that predominately couple to infrared phonons. These vibronic quantum beats, together with first-principles modeling of phonon periodically modulated Rashba parameters, identify a {\em three-fold} excitonic fine structure splitting, i.e., optically-forbidden, degenerate dark states in between two bright ones. Harnessing of vibronic quantum coherence and symmetry inspires light-perovskite quantum control and sub-THz-cycle "Rashba engineering" of spin-split bands for ultimate multi-function device.
- arXiv:1906.06987 (replaced) [pdf, other]
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Title: Home-range search provides advantage under high uncertaintySubjects: Statistical Mechanics (cond-mat.stat-mech); Biological Physics (physics.bio-ph)
Many search processes are conducted in the vicinity of a favored location, i.e., a home, which is visited repeatedly. Foraging animals return to their dens and nests to rest, scouts return to their bases to resupply, and drones return to their docking stations to recharge or refuel. Yet, despite its prevalence, very little is known about home-range search as its analysis is much more challenging than that of unconstrained, free-range, search. Some attempts to treat the home-range problem have been made, but simplifying assumptions cripple existing models and render them inadequate for the description of realistic scenarios. To this end, we develop a theoretical framework for home-range search. This makes no assumptions on the underlying search process and is furthermore suited to treat generic return and home-stay strategies. We show that the solution to the home-range problem can then be given in terms of the solution to the corresponding free-range problem---which not only reduces overall complexity but also gives rise to a simple, and universal, phase-diagram for search. This reveals that home-range search outperforms free-range search in conditions of high uncertainty. Thus, when living gets rough, a home will not only provide warmth and shelter but also allow one to locate food and other resources quickly and more efficiently than in its absence.
- arXiv:1907.01893 (replaced) [pdf, other]
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Title: Process of equilibration in many-body isolated systems: Diagonal versus thermodynamic entropyComments: The original version has been divided in two separate papers, this is the first oneSubjects: Chaotic Dynamics (nlin.CD); Statistical Mechanics (cond-mat.stat-mech); Quantum Physics (quant-ph)
As recently manifested , the quench dynamics of isolated quantum systems consisting of a finite number of particles, is characterized by an exponential spreading of wave packets in the many-body Hilbert space. This happens when the inter-particle interaction is strong enough, thus resulting in a chaotic structure of the many-body eigenstates considered in an unperturbed basis. The semi-analytical approach used here, allows one to estimate the rate of the exponential growth as well as the relaxation time, after which the equilibration (thermalization) emerges. The key ingredient parameter in the description of this process is the width $\Gamma$ of the Local Density of States (LDoS) defined by the initially excited state, the number of particles and the interaction strength. In this paper we show that apart from the meaning of $\Gamma$ as the decay rate of survival probability, the width of the LDoS is directly related to the diagonal entropy and the latter can be linked to the thermodynamic entropy of a system equilibrium state emerging after the complete relaxation. The analytical expression relating the two entropies is derived phenomenologically and numerically confirmed in a model of bosons with random two-body interaction, as well as in a deterministic model which becomes completely integrable in the continuous limit.
- arXiv:1907.02856 (replaced) [pdf, ps, other]
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Title: Impurity scattering induced carrier transport in twisted bilayer grapheneComments: 7 pages, 6 figures (Expanded version for publication)Journal-ref: Phys. Rev. Research 2, 013342 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We theoretically calculate the impurity-scattering induced resistivity of twisted bilayer graphene at low twist angles where the graphene Fermi velocity is strongly suppressed. We consider, as a function of carrier density, twist angle, and temperature, both long-ranged Coulomb scattering and short-ranged defect scattering within a Boltzmann theory relaxation time approach. For experimentally relevant disorder, impurity scattering contributes a resistivity comparable to (much larger than) the phonon scattering contribution at high (low) temperatures. Decreasing twist angle leads to larger resistivity, and in general, the resistivity increases (decreases) with increasing temperature (carrier density). Inclusion of the van Hove singularity in the theory leads to a strong increase in the resistivity at higher densities, where the chemical potential is close to a van Hove singularity, leading to an apparent density-dependent plateau type structure in the resistivity, which has been observed in recent transport experiments. We also show that the Matthissen's rule is strongly violated in twisted bilayer graphene at low twist angles.
- arXiv:1907.12712 (replaced) [pdf, ps, other]
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Title: On the delta function broadening in the Kubo-Greenwood equationAuthors: Pavlo BulanchukSubjects: Disordered Systems and Neural Networks (cond-mat.dis-nn); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Understanding DC electrical conductivity is crucial for the study of materials. Macroscopic DC conductivity can be calculated from first principles using the Kubo-Greenwood equation. The procedure involves finding the thermodynamic limit of the current response to an electric field that is slowly switched on, and then taking the limit of the switching rate to zero. We introduce a nonlinear extrapolation procedure executed in systems with periodic boundary conditions, which predicts conductivity close to the thermodynamic limit even for very small systems. The scheme also overcomes a large part of the usual ambiguities of the DC conductivity definition for finite systems. We numerically compare our method to the Landauer equation-based approach and find both techniques to be consistent with each other.
- arXiv:1909.12402 (replaced) [pdf, other]
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Title: Landauer transport as a quasisteady state on finite chains under unitary quantum dynamicsComments: 19 pages, 14 figuresJournal-ref: Phys. Rev. B 101, 104203 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Disordered Systems and Neural Networks (cond-mat.dis-nn)
In this paper, we study the emergence of a Landauer transport regime from the quantum-mechanical dynamics of free electrons in a disordered tight-binding chain, which is coupled to finite leads with open boundaries. Both partitioned and partition-free initial conditions are analyzed and seen to give rise, for large enough leads, to the same spatially uniform quasi-steady-state current, which agrees with the Landauer value. The quasi-steady-state regime is preceded by a transient regime, which last for a time proportional to the length of the disordered sample, and followed by recursions, after a time that is proportional to the lead size. These theoretical predictions may be of interest to future experiments on transport of fermionic ultra-cold atoms across optical lattices. We also observe finite-size current oscillations, superimposed on the quasi-steady-state, whose behavior depends crucially on the conditions initially imposed on the system. Finally, we show how a time-resolved Kubo formula is able to reproduce this Landauer transport regime, as the leads grow bigger.
- arXiv:1910.01345 (replaced) [pdf]
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Title: Observation of non-Abelian nodal links in photonicsAuthors: Erchan Yang, Biao Yang, Oubo You, Hsun-chi Chan, Peng Mao, Qinghua Guo, Shaojie Ma, Lingbo Xia, Dianyuan Fan, Yuanjiang Xiang, Shuang ZhangComments: 18 pages, 4 figuresSubjects: Optics (physics.optics); Other Condensed Matter (cond-mat.other)
In crystals, two bands may cross each other and form degeneracies along a closed loop in the three-dimensional momentum space, which is called nodal line. Nodal line degeneracy can be designed to exhibit various configurations such as nodal rings, chains, links and knots. Very recently, non-Abelian band topology was proposed in nodal link systems, where the nodal lines formed by consecutive pairs of bands exhibit interesting braiding structures and the underlying topological charges are described by quaternions. Here, we experimentally demonstrate non-Abelian nodal links in a biaxial hyperbolic metamaterial. The linked nodal lines threading through each other are formed by the crossings between three adjacent bands. Based on the non-Abelian charges, we further analyze various admissible nodal link configurations for the three-band system. On the interface between the metamaterial and air, surface bound states in the continuum (BICs) are observed, which serves as the symmetry-enforced derivative of drumhead surface states from the linked nodal lines. Our work serves as a direct observation of the global topological structures of nodal links, and provides a platform for studying non-Abelian topological charge in the momentum space.
- arXiv:1910.05281 (replaced) [pdf, other]
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Title: Scale invariant solidsComments: matching the version published in PRDJournal-ref: Phys. Rev. D 101, 086005 (2020)Subjects: High Energy Physics - Theory (hep-th); Soft Condensed Matter (cond-mat.soft); Strongly Correlated Electrons (cond-mat.str-el)
Scale invariance (SI) can in principle be realized in the elastic response of solid materials. There are two basic options: that SI is a manifest symmetry or that it is spontaneously broken. The manifest case corresponds physically to the existence of a non-trivial infrared fixed point with phonons among its degrees of freedom. We use simple bottom-up AdS/CFT constructions to model this case. We characterize the types of possible elastic response and discuss how the sound speeds can be realistic, that is, sufficiently small compared to the speed of light. We also study the spontaneously broken case using Effective Field Theory (EFT) methods. We present a new one-parameter family of nontrivial EFTs that includes the previously known `conformal solid' as a particular case as well as others which display small sound speeds. We also point out that an emergent Lorentz invariance at low energies could affect by order-one factors the relation between sound speeds and elastic moduli.
- arXiv:1910.06298 (replaced) [pdf, ps, other]
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Title: Inverse Currents in Hamiltonian Coupled TransportComments: 4+2 pagesJournal-ref: Phys. Rev. Lett. 124, 110607 (2020)Subjects: Statistical Mechanics (cond-mat.stat-mech); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
The occurrence of an inverse current, where the sign of the induced current is opposite to the applied force, is a highly counterintuitive phenomenon. We show that inverse currents in coupled transport (ICC) of energy and particle can occur in a one-dimensional interacting Hamiltonian system when its equilibrium state is perturbed by coupled thermodynamic forces. This seemingly paradoxical result is possible due to the self-organization occurring in the system in response to the applied forces.
- arXiv:1910.10180 (replaced) [pdf, other]
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Title: Identifying Higher Order Topology and Fractional Corner Charge Using Entanglement SpectraComments: 11+4 pages, 8 figures in the main text, 3 figures in appendicesJournal-ref: Phys. Rev. B 101, 115140 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Strongly Correlated Electrons (cond-mat.str-el)
We study the entanglement spectrum (ES) of two-dimensional $C_{n}$-symmetric second-order topological insulators (TIs). We show that some characteristic higher order topological observables, e.g., the filling anomaly and its associated fractional corner charge, can be determined from the ES of atomic and fragile TIs. By constructing the relationship between the configuration of Wannier orbitals and the number of protected in-gap states in the ES for different symmetric cuts in real space, we express the fractional corner charge in terms of the number of protected in-gap states of the ES. We show that our formula is robust in the presence of electron-electron interactions as long as the interactions preserve $C_{n}$ rotation symmetry and charge-conservation symmetry. Moreover, we discuss the possible signatures higher order topology in the many-body ES. Our methods allow the identification of some classes of higher order topology without requiring the usage of nested Wilson loops or nested entanglement spectra.
- arXiv:1910.14309 (replaced) [pdf, other]
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Title: Local and non-local electron dynamics of Au/Fe/MgO(001) heterostructures analyzed by time-resolved two-photon photoemission spectroscopyAuthors: Yasin Beyazit, Jan Beckord, Ping Zhou, Jan Meyburg, Detlef Diesing, Manuel Ligges, Uwe BovensiepenComments: 5 pages, 4 figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci)
Employing femtosecond laser pulses in front and back side pumping of Au/Fe/MgO(001) combined with detection in two-photon photoelectron emission spectroscopy we analyze local relaxation dynamics of excited electrons in buried Fe, injection into Au across the Fe-Au interface, and electron transport across the Au layer at 0.6 to 2.0 eV above the Fermi energy. By analysis as a function of Au film thickness we obtain the electron lifetimes of bulk Au and Fe and distinguish the relaxation in the heterostructure's constituents. We also show that the excited electrons propagate through Au in a superdiffusive regime and conclude further that electron injection across the epitaxial interface proceeds ballistically by electron wavepacket propagation.
- arXiv:1911.00427 (replaced) [pdf, other]
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Title: Large Deviations and Fluctuation Theorem for the Quantum Heat CurrentComments: 8(+8) pages, 5 figuresJournal-ref: Phys. Rev. E 101, 052116 (2020)Subjects: Statistical Mechanics (cond-mat.stat-mech); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Quantum Physics (quant-ph)
We study the heat current flowing between two baths consisting of harmonic oscillators interacting with a qubit through a spin-boson coupling. An explicit expression for the generating function of the total heat flowing between the hot and cold baths is derived by evaluating the corresponding Feynman-Vernon path integral under the non-interacting blip approximation (NIBA). This generating function satisfies the Gallavotti-Cohen fluctuation theorem, both before and after performing the NIBA. We also verify that the heat conductivity is proportional to the variance of the heat current, retrieving the well known fluctuation dissipation relation. Finally, we present numerical results for the heat current.
- arXiv:1911.01945 (replaced) [pdf, other]
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Title: Fermi surface reconstruction and electron dynamics at the charge-density-wave transition in TiSe2Authors: Patrick Knowles, Bo Yang, Takaki Muramatsu, Owen Moulding, Jonathan Buhot, Charles Sayers, Enrico Da Como, Sven FriedemannComments: 15 pages, 3 figures, including supplementary informationJournal-ref: Phys. Rev. Lett. 124, 167602 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el)
The evolution of the charge carrier concentrations and mobilities are examined across the charge-density-wave (CDW) transition in TiSe2. Combined quantum oscillation and magnetotransport measurements show that a small electron pocket dominates the electronic properties at low temperatures whilst an electron and hole pocket contribute at room temperature. At the CDW transition, an abrupt Fermi surface reconstruction and a minimum in the electron and hole mobilities are extracted from two-band and Kohler analysis of magnetotransport measurements. The minimum in the mobilities is associated with the overseen role of scattering from the softening CDW mode. With the carrier concentrations and dynamics dominated by the CDW and the associated bosonic mode, our results highlight TiSe2 as a prototypical system to study the Fermi surface reconstruction at a density-wave transition.
- arXiv:1911.02437 (replaced) [pdf, other]
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Title: Bumps and Oscillons in Networks of Spiking NeuronsComments: 13 pages, 11 figuresSubjects: Pattern Formation and Solitons (nlin.PS); Disordered Systems and Neural Networks (cond-mat.dis-nn); Dynamical Systems (math.DS); Biological Physics (physics.bio-ph)
We study localized patterns in an exact mean-field description of a spatially-extended network of quadratic integrate-and-fire (QIF) neurons. We investigate conditions for the existence and stability of localized solutions, so-called bumps, and give an analytic estimate for the parameter range where these solutions exist in parameter space, when one or more microscopic network parameters are varied. We develop Galerkin methods for the model equations, which enable numerical bifurcation analysis of stationary and time-periodic spatially-extended solutions. We study the emergence of patterns composed of multiple bumps, which are arranged in a snake-and-ladder bifurcation structure if a homogeneous or heterogeneous synaptic kernel is suitably chosen. Furthermore, we examine time-periodic, spatially-localized solutions (oscillons) in the presence of external forcing, and in autonomous, recurrently coupled excitatory and inhibitory networks. In both cases we observe period doubling cascades leading to chaotic oscillations.
- arXiv:1911.02909 (replaced) [pdf, other]
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Title: Exciton diffusion in monolayer semiconductors with suppressed disorderAuthors: Jonas Zipfel, Marvin Kulig, Raül Perea-Causín, Samuel Brem, Jonas D. Ziegler, Roberto Rosati, Takashi Taniguchi, Kenji Watanabe, Mikhail M. Glazov, Ermin Malic, Alexey ChernikovJournal-ref: Phys. Rev. B 101, 115430 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci)
Tightly bound excitons in monolayer semiconductors represent a versatile platform to study two-dimensional propagation of neutral quasiparticles. Their intrinsic properties, however, can be severely obscured by spatial energy fluctuations due to a high sensitivity to the immediate environment. Here, we take advantage of the encapsulation of individual layers in hexagonal boron nitride to strongly suppress environmental disorder. Diffusion of excitons is then directly monitored using time- and spatially-resolved emission microscopy at ambient conditions. We consistently find very efficient propagation with linear diffusion coefficients up to 10\,cm$^2$/s, corresponding to room temperature effective mobilities as high as 400\,cm$^2$/Vs as well as a correlation between rapid diffusion and short population lifetime. At elevated densities we detect distinct signatures of many-particle interactions and consequences of strongly suppressed Auger-like exciton-exciton annihilation. A combination of analytical and numerical theoretical approaches is employed to provide pathways towards comprehensive understanding of the observed linear and non-linear propagation phenomena. We emphasize the role of dark exciton states and present a mechanism for diffusion facilitated by free electron hole plasma from entropy-ionized excitons.
- arXiv:1911.11117 (replaced) [pdf, other]
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Title: Quantum algorithms for disordered physicsComments: 5 pages, 5 figures; version for PRAJournal-ref: Phys. Rev. A 101, 032325 (2020)Subjects: Disordered Systems and Neural Networks (cond-mat.dis-nn); High Energy Physics - Lattice (hep-lat); Quantum Physics (quant-ph)
We show how a quantum computer may efficiently simulate a disordered Hamiltonian, by incorporating a pseudo-random number generator directly into the time evolution circuit. This technique is applied to quantum simulation of few-body disordered systems in the large volume limit; in particular, Anderson localization. The method requires a number of (error corrected) qubits proportional to the logarithm of the volume of the system, and each time evolution step requires a number of gates polylogarithmic in the volume. We simulate the method to observe the metal-insulator transition on a three-dimensional lattice. Additionally, we demonstrate the algorithm on a one-dimensional lattice, using physical quantum processors.
- arXiv:1912.04191 (replaced) [pdf, other]
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Title: Spin fine-structure reveals bi-exciton geometry in an organic semiconductorAuthors: K.M. Yunusova, S. L. Bayliss, T. Chanelière, V. Derkach, J. E. Anthony, A.D. Chepelianskii, L. R. WeissSubjects: Materials Science (cond-mat.mtrl-sci); Quantum Physics (quant-ph)
In organic semiconductors, bi-excitons are key intermediates in carrier-multiplication and exciton annihilation. Their local geometry governs their electronic properties and yet has been challenging to determine. Here, we access the structure of the recently discovered $S=2$ quintet bi-exciton state in an organic semiconductor using broadband optically detected magnetic resonance. We correlate the experimentally extracted spin structure with the molecular crystal geometry to identify the specific molecular pairings on which bi-exciton states reside.
- arXiv:1912.04598 (replaced) [pdf, other]
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Title: Emergent force in a bilayer superfluid Bose-Fermi mixtureAuthors: Mehmet GünayComments: 5 pages, 4 figuresSubjects: Quantum Gases (cond-mat.quant-gas); Superconductivity (cond-mat.supr-con); Atomic and Molecular Clusters (physics.atm-clus)
We investigate a system of two-atomic species in mixed dimensions, in which one species is spread in a three-dimensional space and the other species is confined in two parallel layers. The presence of atoms in 3-dimensions creates an induced potential for the ones confined in layers. Depending on the effective scattering length and the layer separation, the formation of p-wave pairing within the same layer or s-wave pairing between different layers has been suggested. It is shown that these pairs cannot coexist when time-reversal symmetry (TRS) is on, and there appears a transition from p-wave to s-wave as the ratio of the layer separation and the effective scattering length decreases. With the formation of the inter-layer pairing, we find an emergent force to be present at the critical point and show that it can be derived from the thermodynamic potential. This result offers a tool for experimentally realizing such transitions, and can find notable potential in the field of quantum-thermodynamics.
- arXiv:2001.00942 (replaced) [pdf, other]
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Title: Simple explanation of Landauer's bound and its ineffectiveness for multivalued logicComments: 13 pages, 8 figuresSubjects: Statistical Mechanics (cond-mat.stat-mech); Materials Science (cond-mat.mtrl-sci); Information Theory (cs.IT); Mathematical Physics (math-ph)
We discuss, using recent results on the Landauer's bound in multivalued logic, the difficulties and pitfalls of how to apply this principle. The presentation is based on Szilard's version of Maxwell's demon experiment and use of equilibrium Thermodynamics. Different versions of thermodynamical/mechanical memory are presented - one-hot encoding version and the implementation based on reversed Szilard's experiment. Relation of the Landauer's principle to Galois connection is explained in detail.
- arXiv:2001.09039 (replaced) [pdf, other]
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Title: Electronic and magnetic properties of 3$d$ transition-metal adatoms on Mn/W(110)Journal-ref: Phys. Rev. B 101, 134411 (2020)Subjects: Materials Science (cond-mat.mtrl-sci); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Using density functional theory, we investigate the electronic and magnetic properties of $3d$ transition-metal adatoms adsorbed on a monolayer of Mn on W(110). Mn/W(110) has a noncollinear cycloidal spin-spiral ground state with an angle of 173$^\circ$ between magnetic moments of adjacent Mn rows. It allows to rotate the spin orientation of an adsorbed magnetic adatom quasi-continuously. Therefore, this surface is ideally suited for manipulating the spin direction of individual atoms and exploring their magnetic properties using scanning tunneling microscopy (STM). The adsorbed V and Cr transition-metal adatoms couple antiferromagnetically to the nearest neighbor Mn atom of Mn monolayer while Mn, Fe, Co, and Ni couple ferromagnetically. The magnetic moments of the $3d$ adatoms are large and show a Hund's rule type of trend with a peak in the middle of the series. We find large spin splitting of the $3d$ transition-metal adatoms, large spin polarization of the local vacuum density of states up to 73\% at the Fermi energy, and significant tunneling anisotropic magnetoresistance enhancement up to 27\%. We conclude that such large values stem from the strong hybridization between the adatoms and the Mn atoms of the monolayer. Furthermore, identification of spin orientations of the adatom using spin-polarized STM is only possible for Co and V adatoms.
- arXiv:2001.09512 (replaced) [pdf, other]
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Title: Pulse percolation conduction and multi-value memoryComments: 5 pages, 7 figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Disordered Systems and Neural Networks (cond-mat.dis-nn)
We develop a theory of pulse conduction in percolation type of materials such as noncrystalline semiconductors and nano-metal compounds. For short voltage pulses, the corresponding electric currents are inversely proportional to the pulse length and exhibit significant nonohmicity due to strong local fields in resistive regions of the percolation bonds. These fields can trigger local switching events incrementally changing bond resistances in response to pulse trains. Our prediction opens a venue to a class of multi-value nonvolatile memory implementable with a variety of materials.
- arXiv:2002.03000 (replaced) [pdf, other]
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Title: Parallel PERMSubjects: Statistical Mechanics (cond-mat.stat-mech); Soft Condensed Matter (cond-mat.soft)
We develop and implement a parallel flatPERM algorithm \cite{G97,PK04} with mutually interacting parallel flatPERM sequences and use it to sample self-avoiding walks in 2 and 3 dimensions. Our data show that the parallel implementation accelerates the convergence of the flatPERM algorithm. Moreover, increasing the number of interacting flatPERM sequences (rather than running longer simulations) improves the rate of convergence. This suggests that a more efficient implementation of flatPERM will be a massively parallel implementation, rather than long simulations of one, or a few parallel sequences. We also use the algorithm to estimate the growth constant of the self-avoiding walk in two and in three dimensions using simulations over 12 parallel sequences. Our best results are \[ \mu_d = \cases{ 2.6381585(1), & \hbox{if $d=2$}; \cr 4.684039(1), & \hbox{if $d=3$}. } \]
- arXiv:2002.06528 (replaced) [pdf, other]
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Title: Combining high-performance hardware, cloud computing, and deep learning frameworks to accelerate physical simulations: probing the Hopfield networkAuthors: Vaibhav VavilalaComments: 23 pages, 4 figures. Eur. J. Phys (2020)Subjects: Computational Physics (physics.comp-ph); Disordered Systems and Neural Networks (cond-mat.dis-nn)
The synthesis of high-performance computing (particularly graphics processing units), cloud computing services (like Google Colab), and high-level deep learning frameworks (such as PyTorch) has powered the burgeoning field of artificial intelligence. While these technologies are popular in the computer science discipline, the physics community is less aware of how such innovations, freely available online, can improve research and education. In this tutorial, we take the Hopfield network as an example to show how the confluence of these fields can dramatically accelerate physics-based computer simulations and remove technical barriers in implementing such programs, thereby making physics experimentation and education faster and more accessible. To do so, we introduce the cloud, the GPU, and AI frameworks that can be easily repurposed for physics simulation. We then introduce the Hopfield network and explain how to produce large-scale simulations and visualizations for free in the cloud with very little code (fully self-contained in the text). Finally, we suggest programming exercises throughout the paper, geared towards advanced undergraduate students studying physics, biophysics, or computer science.
- arXiv:2002.07329 (replaced) [pdf]
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Title: Stick-slip Avalanches in Steady Shearing: Signature of Transition between Granular Fluid and SolidSubjects: Soft Condensed Matter (cond-mat.soft); Fluid Dynamics (physics.flu-dyn)
By observing the fluctuations of fluid-immersed granular particles upon steady shearing, we identify a transitional zone that sets the system apart from fluidic sliding and signals the onset of solid mechanics, as the shear rate decreases. Toward the slow extreme, statistical analyses of the avalanche events combined with internal imaging capture the continuous yet distinctive change of behaviors, and offer test grounds for theories on the development of plasticity. We link such transition with the velocity weakening of inter-particle frictions, and propose a three-state phase diagram that bridges our discoveries on tightly packed granular systems and previous understanding of suspension rheology.
- arXiv:2002.10156 (replaced) [pdf, other]
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Title: Upper critical field in ferromagnetic metals with triplet pairingAuthors: V.P. MineevComments: The paper targeted for the AoP special issue in honour of G.M.Eliashberg 90 jubilee (9pages,1figure)Subjects: Superconductivity (cond-mat.supr-con)
The theory of triplet superconductivity in ferromagnetic metals based on electron-electron interaction by spin fluctuation exchange is developed. The equations for the upper critical field temperature dependence are derived. In contrast to the similar equations for the superconductivity in two band metals they contain the pairing amplitudes and the Fermi velocities depending on magnetic field. The critical field behaviour near the critical temperature and at T = 0 is established analytically.
- arXiv:2003.03555 (replaced) [pdf, other]
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Title: Honeycomb Layered Oxides: Structure, Energy Storage, Transport, Topology and Relevant InsightsAuthors: Godwill Mbiti Kanyolo, Titus Masese, Nami Matsubara, Chih-Yao Chen, Josef Rizell, Ola Kenji Forslund, Elisabetta Nocerino, Konstantinos Papadopoulos, Anton Zubayer, Minami Kato, Kohei Tada, Keigo Kubota, Hiroshi Senoh, Zhen-Dong Huang, Yasmine Sassa, Martin Mansson, Hajime Matsumoto, Qiang XuComments: 53 pages, 21 figures, 1 table, review manuscriptSubjects: Materials Science (cond-mat.mtrl-sci)
The advent of nanotechnology has hurtled the discovery and development of nanostructured materials with stellar chemical and physical functionalities in a bid to address issues in energy, environment, telecommunications and healthcare. In this quest, honeycomb layered oxides have emerged as materials exhibiting fascinatingly rich crystal chemistry and play host to varied exotic electromagnetic and topological phenomena. These oxide materials, consisting mainly of alkali metal or coinage metal atoms sandwiched between slabs of transition metal atoms arranged in a honeycomb fashion, are of great utility and diverse interest in a multiple fields ranging from materials science, solid-state chemistry, electrochemistry to condensed matter physics. Currently, with a niche application in energy storage as high-voltage materials, the honeycomb layered oxides serve as ideal pedagogical exemplars of the innumerable capabilities of nanomaterials. In this Review, we delineate the relevant chemistry and physics of honeycomb layered oxides, and discuss their functionalities for tunable electrochemistry, superfast ionic conduction, optics, electromagnetism and topology. Moreover, we elucidate the unexplored albeit vastly promising crystal chemistry space whilst outlining effective ways to identify regions within this compositional space, particularly where interesting electromagnetic and topological properties could be lurking within the aforementioned alkali and coinage-metal honeycomb layered oxide structures. We conclude by pointing towards possible future research directions, particularly the prospective realisation of Kitaev-Heisenberg-Dzyaloshinskii-Moriya interactions with single crystals and Floquet theory in closely-related honeycomb layered oxide materials.
- arXiv:2003.08531 (replaced) [pdf, other]
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Title: Evolution of the structural transition in Mo$_{1-x}$W$_{x}$Te$_{2}$Authors: John A. Schneeloch, Yu Tao, Chunruo Duan, Masaaki Matsuda, Adam A. Aczel, Jaime A. Fernandez-Baca, Guangyong Xu, Jörg C. Neuefeind, Junjie Yang, Despina LoucaComments: supplement in separate fileSubjects: Materials Science (cond-mat.mtrl-sci)
The composition dependence of the structural transition between the monoclinic 1T$^{\prime}$ and orthorhombic T$_{d}$ phases in the Mo$_{1-x}$W$_{x}$Te$_{2}$ Weyl semimetal was investigated by elastic neutron scattering on single crystals up to $x \approx 0.54$. First observed in MoTe$_{2}$, the transition from T$_{d}$ to 1T$^{\prime}$ is accompanied by an intermediate pseudo-orthorhombic phase, T$_{d}^{*}$. Upon doping with W the T$_{d}^{*}$ phase vanishes by $x \approx 0.34$. Above this concentration, a phase coexistence behavior with both T$_{d}$ and 1T$^{\prime}$ is observed, instead. The interlayer in-plane positioning parameter, $\delta$, which relates to the 1T$^{\prime}$ $\beta$ angle, decreases with temperature as well as with W substitution indicating strong anharmonicity of the layer displacements. The temperature width of the phase coexistence remains almost constant up to $x \approx 0.54$, in contrast to the broadening reported with applying pressure.
- arXiv:1704.00313 (replaced) [pdf, ps, other]
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Title: First-principles prediction of the stacking fault energy of gold at finite temperatureComments: 9 pages, 4 figuresJournal-ref: Acta Mater. 135 (2017) 88-95Subjects: Materials Science (cond-mat.mtrl-sci)
The intrinsic stacking fault energy (ISFE) $\gamma$ is a material parameter fundamental to the discussion of plastic deformation mechanisms in metals. Here, we scrutinize the temperature dependence of the ISFE of Au through accurate first-principles derived Helmholtz free energies employing both the super cell approach and the axial Ising model (AIM). A significant decrease of the ISFE with temperature, $-(36$-$39)$\,\% from 0 to 890\,K depending on the treatment of thermal expansion, is revealed, which matches the estimate based on the experimental temperature coefficient $d \gamma / d T $ closely. We make evident that this decrease predominantly originates from the excess vibrational entropy at the stacking fault layer, although the contribution arising from the static lattice expansion compensates it by approximately 60\,\%. Electronic excitations are found to be of minor importance for the ISFE change with temperature. We show that the Debye model in combination with the AIM captures the correct sign but significantly underestimates the magnitude of the vibrational contribution to $\gamma(T)$. The hexagonal close-packed (hcp) and double hcp structures are established as metastable phases of Au. Our results demonstrate that quantitative agreement with experiments can be obtained if all relevant temperature-induced excitations are considered in first-principles modeling and that the temperature dependence of the ISFE is substantial enough to be taken into account in crystal plasticity modeling.
- arXiv:1803.04178 (replaced) [pdf, ps, other]
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Title: Understanding the mechanical properties of reduced activation steelsComments: 29 pages, 4 figuresJournal-ref: Materials & Design 146 (2018) 260-272Subjects: Materials Science (cond-mat.mtrl-sci)
Reduced activation ferritic/martensitic (RAFM) steels are structural materials with potential application in Generation-IV fission and fusion reactors. We use density-functional theory to scrutinize the micro-mechanical properties of the main alloy phases of three RAFM steels based on the body-centered cubic FeCrWVMn solid solution. We assess the lattice parameters and elastic properties of ferromagnetic $\alpha$-Fe and Fe$_{91}$Cr$_{9}$, which are the main building blocks of the RAFM steels, and present a detailed analysis of the calculated alloying effects of V, Cr, Mn, and W on the mechanical properties of Fe$_{91}$Cr$_{9}$. The composition dependence of the elastic parameters is decomposed into electronic and volumetric contributions and studied for alloying levels that cover the typical intervals in RAFM steels. A linear superposition of the individual solute effects on the properties of Fe$_{91}$Cr$_{9}$ is shown to provide an excellent approximation for the \emph{ab initio} values obtained for the RAFM steels. The intrinsic ductility is evaluated through Rice's phenomenological theory using the surface and unstable stacking fault energies, and the predictions are contrasted with those obtained by empirical criteria. Alloying with V or W is found to enhance the ductility, whereas additional Cr or Mn turns the RAFM base alloys more brittle.
- arXiv:1804.05581 (replaced) [pdf]
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Title: Calculation of impurity density and electron-spin relaxation times in p-type GaAs:MnAuthors: Veronika BurobinaComments: 13 pages, 1 table, 1 figureJournal-ref: Materials Science & Engineering B 255 (2020) 114518Subjects: Materials Science (cond-mat.mtrl-sci)
Magnetic semiconductors have aroused interest due to their various functionalities related to spintronic devices. Manganese (Mn) as a substitutional impurity in A3B5 semiconductors supplies not only holes, but also localized spins. The ejection of Mn atoms with an uncompensated magnetic moment leads to the appearance of ferromagnetic properties. The most suitable material characterized by long-term spin dynamics is n-type GaAs. In p-type GaAs, the spin relaxation time of electrons is generally much shorter. For purposes of this research, electron-spin relaxation times in 3D and 2D p-type GaAs were studied. Calculation of impurity densities and charge state of magnetic acceptors demonstrate the essential composition of the material. Comparison of theoretical and experimental data in optical-spin orientation of electrons reveal the longest spin relaxation time of 77 ns in 2D GaAs:Mn, less than twice the best time in the p-type 3D GaAs material.
- arXiv:1903.01388 (replaced) [pdf, other]
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Title: 500 microkelvin nanoelectronicsComments: Supplementary Information is available as ancillary file, raw data and calculations can be downloaded from this http URLJournal-ref: Nat Commun 11, 1492 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Applied Physics (physics.app-ph); Instrumentation and Detectors (physics.ins-det)
Fragile quantum effects such as single electron charging in quantum dots or macroscopic coherent tunneling in superconducting junctions are the basis of modern quantum technologies. These phenomena can only be observed in devices where the characteristic spacing between energy levels exceeds the thermal energy, $k_\textrm{B}T$, demanding effective refrigeration techniques for nanoscale electronic devices. Commercially available dilution refrigerators have enabled typical electron temperatures in the $10\ldots100\,$mK regime, however indirect cooling of nanodevices becomes inefficient due to stray radiofrequency heating and weak thermal coupling of electrons to the device substrate. Here we report on passing the millikelvin barrier for a nanoelectronic device. Using a combination of on-chip and off-chip nuclear refrigeration, we reach an ultimate electron temperature of $T_e=421\pm35\,\mu$K measured by a Coulomb-blockade thermometer. With a hold time exceeding $85\,$hours below $700\,\mu$K, we provide a landmark demonstration of nanoelectronics in the microkelvin regime.
- arXiv:1903.05099 (replaced) [pdf, other]
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Title: Many-body dynamics in long-range hopping model in the presence of correlated and uncorrelated disorderComments: 5 pages, 3 figures, Accepted for publication in Phys. Rev. Research as Rapid CommunicationJournal-ref: Phys. Rev. Research 2, 012074 (2020)Subjects: Disordered Systems and Neural Networks (cond-mat.dis-nn); Quantum Gases (cond-mat.quant-gas); Statistical Mechanics (cond-mat.stat-mech)
Much have been learned about universal properties of entanglement entropy (EE) and participation ration (PR) for Anderson localization. We find a new sub-extensive scaling with system size of the above measures for algebraic localization as noticed in one-dimensional long-range hopping models in the presence of uncorrelated disorder. While the scaling exponent of EE seems to vary universally with the long distance localization exponent of single particle states (SPSs), PR does not show such university as it also depends on the short range correlations of SPSs. On the other hand, in presence of correlated disorder, an admixture of two species of SPSs (ergodic delocalized and non-ergodic multifractal or localized) are observed, which leads to extensive (sub-extensive) scaling of EE (PR). Considering typical many-body eigenstates, we obtain above results that are further corroborated with the asymptotic dynamics. Additionally, a finite time secondary slow growth in EE is witnessed only for correlated case while for uncorrelated case there exists only primary growth followed by the saturation. We believe that our findings from typical many-body eigenstate would remain unaltered even in the weakly interacting limit.
- arXiv:1907.02939 (replaced) [pdf, other]
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Title: Optimal cycles for low-dissipation heat enginesComments: Accepted in PRL. 5 pages +16 Supp.MatJournal-ref: Phys. Rev. Lett. 124, 110606 (2020)Subjects: Quantum Physics (quant-ph); Statistical Mechanics (cond-mat.stat-mech)
We consider the optimization of a finite-time Carnot engine characterized by small dissipations. We bound the power with a simple inequality and show that the optimal strategy is to perform small cycles around a given working point, which can be thus chosen optimally. Remarkably, this optimal point is independent of the figure of merit combining power and efficiency that is being maximized. Furthermore, for a general class of dynamics the power output becomes proportional to the heat capacity of the working substance. Since the heat capacity can scale supra-extensively with the number of constituents of the engine, this enables us to design optimal many-body Carnot engines reaching maximum efficiency at finite power per constituent in the thermodynamic limit.
- arXiv:1907.10321 (replaced) [pdf, ps, other]
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Title: Circles of equal radii randomly placed on a plane: some rigorous results, asymptotic behavior, and application to transparent electrodesComments: 16 pages, 8 figures, 24 referencesJournal-ref: Journal of Statistical Mechanics: Theory and Experiment. 2020. March. Vol. 2020, Iss. 3. P. 033202Subjects: Statistical Mechanics (cond-mat.stat-mech); Disordered Systems and Neural Networks (cond-mat.dis-nn); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We consider $N$ circles of equal radii, $r$, having their centers randomly placed within a square domain $\mathcal{D}$ of size $L \times L$ with periodic boundary conditions ($\mathcal{D} \in \mathbb{R}^2$). When two or more circles intersect each other, each circle is divided by the intersection points into several arcs. We found the exact length distribution of the arcs. In the limiting case of dense systems and large size of the domain $\mathcal{D}$ ($L \to \infty$ in such a way that the number of circle per unit area, $n=N/L^2$, is constant), the arc distribution approaches the probability density function (PDF) $f(\psi) = 4 n r^2\exp(-4 n r^2 \psi)$, where $\psi$ is the central angle subtended by the arc. This PDF is then used to estimate the sheet resistance of transparent electrodes based on conductive rings randomly placed onto a transparent insulating film.
- arXiv:1908.03469 (replaced) [pdf, other]
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Title: Unsupervised learning using topological data augmentationComments: 10 pages, 15 figures. Changes include more general topological classification, local topological quantity extraction, added 2d case (Chern class)Journal-ref: Phys. Rev. Research 2, 013354 (2020)Subjects: Disordered Systems and Neural Networks (cond-mat.dis-nn); Strongly Correlated Electrons (cond-mat.str-el); Quantum Physics (quant-ph)
Unsupervised machine learning is a cornerstone of artificial intelligence as it provides algorithms capable of learning tasks, such as classification of data, without explicit human assistance. We present an unsupervised deep learning protocol for finding topological indices of quantum systems. The core of the proposed scheme is a 'topological data augmentation' procedure that uses seed objects to generate ensembles of topologically equivalent data. Such data, assigned with dummy labels, can then be used to train a neural network classifier for sorting arbitrary objects into topological equivalence classes. Our protocol is explicitly illustrated on 2-band insulators in 1d and 2d, characterized by a winding number and a Chern number respectively. By using the augmentation technique also in the classification step we can achieve accuracy arbitrarily close to 100% even for objects with indices outside the training regime.
- arXiv:1909.02714 (replaced) [pdf, other]
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Title: Time-dependent Ginzburg-Landau treatment of RF Magnetic Vortices in Superconductors: Vortex-Semiloops in a Spatially Nonuniform Magnetic FieldJournal-ref: Phys. Rev. E 101, 033306 (2020)Subjects: Superconductivity (cond-mat.supr-con); Computational Physics (physics.comp-ph)
We apply time-dependent Ginzburg Landau (TDGL) numerical simulations to study the finite frequency electrodynamics of superconductors subjected to intense rf magnetic field. Much recent TDGL work has focused on spatially uniform external magnetic field and largely ignores the Meissner state screening response of the superconductor. In this work, we solve the TGDL equations for a spatially non-uniform magnetic field created by a point magnetic dipole in the vicinity of a semi-infinite superconductor. A novel two-domain simulation is performed to accurately capture the effect of the inhomogeneous applied fields and the resulting screening currents. The creation and dynamics of vortex semiloops penetrating deep into the superconductor domain is observed and studied, and the resulting third-harmonic nonlinear response of the sample is calculated. The effect of point-like defects on vortex semi-loop behaviour is also studied. This simulation method will assist our understanding of the limits of superconducting response to intense rf magnetic fields.
- arXiv:1909.09727 (replaced) [pdf]
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Title: Nucleation of Dislocations in 3.9 nm Nanocrystals at High PressureAuthors: Abhinav Parakh, Sangryun Lee, K. Anika Harkins, Mehrdad T. Kiani, David Doan, Martin Kunz, Andrew Doran, Lindsey A. Hanson, Seunghwa Ryu, X. Wendy GuComments: 33 pages, 12 figuresJournal-ref: Phys. Rev. Lett. 124, 106104 (2020)Subjects: Materials Science (cond-mat.mtrl-sci)
As circuitry approaches single nanometer length scales, it is important to predict the stability of metals at these scales. The behavior of metals at larger scales can be predicted based on the behavior of dislocations, but it is unclear if dislocations can form and be sustained at single nanometer dimensions. Here, we report the formation of dislocations within individual 3.9 nm Au nanocrystals under nonhydrostatic pressure in a diamond anvil cell. We used a combination of x-ray diffraction, optical absorbance spectroscopy, and molecular dynamics simulation to characterize the defects that are formed, which were found to be surface-nucleated partial dislocations. These results indicate that dislocations are still active at single nanometer length scales and can lead to permanent plasticity.
- arXiv:1909.13462 (replaced) [pdf]
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Title: Hall coefficient diagnostics of surface state in pressurized SmB6Authors: Yazhou Zhou, Priscila F. S. Rosa, Jing Guo, Shu Cai, Rong Yu, Sheng Jiang, Ke Yang, Aiguo Li, Qimiao Si, Qi Wu, Zachary Fisk, Liling SunComments: 15 pages, 4 figuresJournal-ref: Phys. Rev. B 101, 125116 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el)
In this study, we report the first results of the high-pressure Hall coefficient (RH) measurements in the putative topological Kondo insulator SmB6 up to 37 GPa. Below 10 GPa, our data reveal that RH(T) exhibits a prominent peak upon cooling below 20 K. Remarkably, the temperature at which surface conduction dominates coincides with the temperature of the peak in RH(T). The temperature dependent resistance and Hall coefficient can be well fitted by a two-channel model with contributions from the metallic surface and the thermally activated bulk states. When the bulk of SmB6 becomes metallic and magnetic at ~ 10 GPa, both the RH(T) peak and the resistance plateau disappear simultaneously. Our results indicate that the RH(T) peak is a fingerprint to diagnose the presence of a metallic surface state in SmB6. The high-pressure magnetic state of SmB6 is robust to 180 GPa, and no evidence of superconductivity is observed in the metallic phase.
- arXiv:1910.09604 (replaced) [pdf, other]
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Title: Lattice gauge theory for Haldane conjecture and central-branch Wilson fermionComments: 24 pages, 2 figures; (v2) discussion improved, refs added; (v3) minor changesJournal-ref: Prog Theor Exp Phys (2020)Subjects: High Energy Physics - Lattice (hep-lat); Strongly Correlated Electrons (cond-mat.str-el); High Energy Physics - Theory (hep-th)
We develop the $(1+1)$d lattice $U(1)$ gauge theory in order to define $2$-flavor massless Schwinger model, and discuss its connection with Haldane conjecture. We propose to use the central-branch Wilson fermion, which is defined by relating the mass, $m$, and the Wilson parameter, $r$, as $m+2r=0$. This setup gives two massless Dirac fermions in the continuum limit, and it turns out that no fine-tuning of $m$ is required because the extra $U(1)$ symmetry at the central branch, $U(1)_{\bar{V}}$, prohibits the additive mass renormalization. Moreover, we show that Dirac determinant is positive semi-definite and this formulation is free from the sign problem, so the Monte Carlo simulation of the path integral is possible. By identifying the symmetry at low energy, we show that this lattice model has the mixed 't Hooft anomaly between $U(1)_{\bar{V}}$, lattice translation, and lattice rotation. We discuss its relation to the anomaly of half-integer anti-ferromagnetic spin chains, so our lattice gauge theory is suitable for numerical simulation of Haldane conjecture. Furthermore, it gives new and strict understanding on parity-broken phase (Aoki phase) of $2$d Wilson fermion.
- arXiv:1911.02307 (replaced) [pdf, other]
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Title: Effect of tunneling on the electrical conductivity of nanowire-based films: computer simulation within a core--shell modelComments: 6 pages, 5 figures, 45 referencesJournal-ref: Journal of Applied Physics. 2019. Vol. 126, No. 24. P. 244903Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Disordered Systems and Neural Networks (cond-mat.dis-nn); Applied Physics (physics.app-ph)
We have studied the electrical conductivity of two-dimensional nanowire networks. An analytical evaluation of the contribution of tunneling to their electrical conductivity suggests that it is proportional to the square of the wire concentration. Using computer simulation, three kinds of resistance were taken into account, viz., (i) the resistance of the wires, (ii) the wire---wire junction resistance, and (iii) the tunnel resistance between wires. We found that the percolation threshold decreased due to tunneling. However, tunneling had negligible effect on the electrical conductance of dense nanowire networks.
- arXiv:1911.12282 (replaced) [pdf]
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Title: Atomic reconstruction and moiré patterns in transition metal dichalcogenide van der Waals heterostructuresAuthors: Matthew R. Rosenberger, Hsun-Jen Chuang, Madeleine Phillips, Vladimir P. Oleshko, Kathleen M. McCreary, Saujan V. Sivaram, C. Stephen Hellberg, Berend T. JonkerComments: 22 pages, 3 figuresSubjects: Materials Science (cond-mat.mtrl-sci); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Van der Waals layered materials, such as transition metal dichalcogenides (TMDs), are an exciting class of materials with weak interlayer bonding which enables one to create van der Waals heterostructures (vdWH). Recent work has shown that control of the twist angle between layers can have a dramatic effect on vdWH properties. For TMD vdWH, twist angle has been treated solely through the use of rigid-lattice moir\'e patterns. No atomic reconstruction, i.e. any rearrangement of atoms within the individual layers, has been reported experimentally to date. Here we demonstrate that vdWH of MoSe2/WSe2 and MoS2/WS2 at twist angles less than 1{\deg} undergo significant atomic level reconstruction leading to discrete commensurate domains divided by narrow domain walls, rather than a smoothly varying rigid-lattice moir\'e pattern as has been assumed in prior work. Using conductive atomic force microscopy (CAFM), we show that the stacking orientation of the two TMD crystals has a profound impact on the atomic reconstruction, consistent with recent theoretical work on graphene/graphene and MoS2/MoS2 structures and experimental work on graphene bilayers and hBN/graphene vdWH. Transmission electron microscopy (TEM) provides additional evidence of atomic reconstruction in MoSe2/WSe2 structures and demonstrates the transition between a rigid-lattice moir\'e pattern for large angles and atomic reconstruction for small angles. We use density functional theory to calculate the band structures of the commensurate reconstructed domains and find that the modulation of the relative electronic band edges is consistent with the CAFM results and photoluminescence spectra from reconstructed vdWH. The presence of atomic reconstruction in TMD heterostructures and the observed impact on nanometer-scale electronic properties provides fundamental insight into the behavior of this important class of heterostructures.
- arXiv:1912.08228 (replaced) [pdf, other]
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Title: Randomly branching $θ$-polymers in two and three dimensions: Average properties and distribution functionsComments: 15 figures, 10 tables, submitted for publicationJournal-ref: The Journal of Chemical Physics 152, 114903 (2020)Subjects: Soft Condensed Matter (cond-mat.soft); Computational Physics (physics.comp-ph)
Motivated by renewed interest in the physics of branched polymers, we present here a complete characterization of the connectivity and spatial properties of $2$ and $3$-dimensional single-chain conformations of randomly branching polymers in $\theta$-solvent conditions obtained by Monte Carlo computer simulations. The first part of the work focuses on polymer average properties, like the average polymer spatial size as a function of the total tree mass and the typical length of the average path length on the polymer backbone. In the second part, we move beyond average chain behavior and we discuss the complete distribution functions for tree paths and tree spatial distances, which are shown to obey the classical Redner-des Cloizeaux functional form. Our results were rationalized first by the systematic comparison to a Flory theory for branching polymers and, next, by generalized Fisher-Pincus relationships between scaling exponents of distribution functions. For completeness, the properties of $\theta$-polymers were compared to their ideal (i.e.), no volume interactions) as well as good-solvent (i.e.), above the $\theta$-point) counterparts. The results presented here brings to conclusion the recent work performed in our group [A. Rosa and R. Everaers, J. Phys. A: Math. Theor. 49, 345001 (2016), J. Chem. Phys. 145, 164906 (2016), Phys. Rev. E 95, 012117 (2017)] in the context of the scaling properties of branching polymers.
- arXiv:2001.05533 (replaced) [pdf, ps, other]
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Title: Quantum critical point in the itinerant ferromagnet Ni$_{1-x}$Rh$_x$Authors: C.-L. Huang, A. M. Hallas, K. Grube, S. Kuntz, B. Spiess, K. Bayliff, T. Besara, T. Siegrist, Y. Cai, J. Beare, G. M. Luke, E. MorosanComments: 15 pages, 4 figuresJournal-ref: Phys. Rev. Lett. 124, 117203 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el)
We report a chemical substitution-induced ferromagnetic quantum critical point in polycrystalline Ni$_{1-x}$Rh$_x$ alloys. Through magnetization and muon spin relaxation measurements, we show that the ferromagnetic ordering temperature is suppressed continuously to zero at $x_{crit} = 0.375$ while the magnetic volume fraction remains 100% up to $x_{crit}$, pointing to a second order transition. Non-Fermi liquid behavior is observed close to $x_{crit}$, where the electronic specific heat $C_{el}/T$ diverges logarithmically, while immediately above $x_{crit}$ the volume thermal expansion coefficient $\alpha_{V}/T$ and the Gr\"uneisen ratio $\Gamma = \alpha_{V}/C_{el}$ both diverge logarithmically in the low temperature limit, further indication of a ferromagnetic quantum critical point in Ni$_{1-x}$Rh$_x$.
- arXiv:2002.07013 (replaced) [pdf, ps, other]
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Title: Ductile and brittle crack-tip response in equimolar refractory high-entropy alloysComments: 32 pages, 7 figuresJournal-ref: Acta Mater. 189 (2020) 174-187Subjects: Materials Science (cond-mat.mtrl-sci)
Understanding the strengthening and deformation mechanisms in refractory high-entropy alloys (HEAs), proposed as new high-temperature material, is required for improving their typically insufficient room-temperature ductility. Here, density-functional theory simulations and a continuum mechanics analysis were conducted to systematically investigate the competition between cleavage decohesion and dislocation emission from a crack tip in the body-centered cubic refractory HEAs HfNbTiZr, MoNbTaVW, MoNbTaW, MoNbTiV, and NbTiVZr. This crack-tip competition is evaluated for tensile loading and a totality of 15 crack configurations and slip systems. Our results predict that dislocation plasticity at the crack tip is generally unfavorable -- although the competition is close for some crack orientations, suggesting intrinsic brittleness and low crack-tip fracture toughness in these five HEAs at zero temperature. Fluctuations in local alloy composition, investigated for HfNbTiZr, can locally reduce the resistance to dislocation emission for a slip system relative to the configuration average of that slip system, but do not change the dominant crack-tip response. In the case of single-crystal MoNbTaW, where an experimental, room-temperature fracture-toughness value is available for a crack on a \{100\} plane, theoretical and experimental results agree favorably. Factors that may limit the agreement are discussed. We survey the effect of material anisotropy on preferred crack tip orientations, which are found to be alloy specific. Mixed-mode loadings are found to shift the competition in favor of cleavage or dislocation nucleation, depending on crack configuration and amplified by the effect of material anisotropy on crack tip stresses.
- arXiv:2002.08283 (replaced) [pdf, other]
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Title: Coherent Band-Edge Oscillations and Dynamic LO Phonon Mode Splitting as Evidence for Polaronic Coupling in PerovskitesAuthors: Z. Liu, C. Vaswani, L. Luo, D. Cheng, X. Yang, X. Zhao, Y. Yao, Z. Song, R. Brenes, R. Kim, J. Jean, V. Bulovic, Y. Yan, K.-M. Ho, J. WangJournal-ref: Phys. Rev. B 101, 115125 (2020)Subjects: Materials Science (cond-mat.mtrl-sci); Other Condensed Matter (cond-mat.other); Strongly Correlated Electrons (cond-mat.str-el)
The coherence of collective modes, such as phonons, and their modulation of the electronic states are long sought in complex systems, which is a cross-cutting issue in photovoltaics and quantum electronics. In photovoltaic cells and lasers based on metal halide perovskites, the presence of polaronic coupling, i.e., photocarriers dressed by the macroscopic motion of charged lattice, assisted by terahertz (THz) longitudinal optical (LO) phonons, has been intensely studied yet still debated. This may be key for explaining the remarkable properties of the perovskite materials, e.g., defect tolerance, long charge lifetimes and diffusion length. Here we use the intense single-cycle THz pulse with the peak electric field up to $E_{THz}=$1000\,kV/cm to drive coherent band-edge oscillations at room temperature in CH$_3$NH$_3$PbI$_3$. We reveal the oscillatory behavior dominantly to a specific quantized lattice vibration mode at $\omega_{\mathrm{LO}}\sim$4 THz, being both dipole and momentum forbidden. THz-driven coherent dynamics exhibits distinguishing features: the room temperature coherent oscillations at $\omega_{\mathrm{LO}}$ longer than 1 ps in both single crystals and thin films; the {\em mode-selective} modulation of different band edge states assisted by electron-phonon ($e$-$ph$) interaction; {\em dynamic mode splitting} controlled by temperature due to entropy and anharmonicity of organic cations. Our results demonstrate intense THz-driven coherent band-edge modulation as a powerful probe of electron-lattice coupling phenomena and provide compelling implications for polaron correlations in perovskites.
- arXiv:2003.03992 (replaced) [pdf]
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Title: Reply to "Comment on 'Apical charge flux-modulated in-plane transport properties of cuprate superconductors'"Journal-ref: Phys. Rev. Lett. 124, 109702 (2020)Subjects: Superconductivity (cond-mat.supr-con)
This Reply to preceding Comment of arXiv:1909.09867 shows why the statements in the Comment are misleading. We point out that our physical picture and theirs are fundamentally different, therefore the claim of using their correlation to include ours shows a very limited physical relevance, which instead may impede the precise understanding of either of the two pictures.
Crosses
- arXiv:2003.08898 (cross-list from math-ph) [pdf, other]
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Title: Classification of topological phases with finite internal symmetries in all dimensionsComments: 34 pages, 6 figuresSubjects: Mathematical Physics (math-ph); Strongly Correlated Electrons (cond-mat.str-el); High Energy Physics - Theory (hep-th); Category Theory (math.CT); Quantum Algebra (math.QA)
We develop a mathematical theory of symmetry protect trivial (SPT) orders and anomaly-free symmetry enriched topological (SET) orders in all dimensions via two different approaches with an emphasis on the second approach. The first approach is to gauge the symmetry in the same dimension by adding topological excitations as it was done in the 2d case, in which the gauging process is mathematically described by the minimal modular extensions of unitary braided fusion 1-categories. This 2d result immediately generalizes to all dimensions except in 1d, which is treated with special care. The second approach is to use the 1-dimensional higher bulk of the SPT/SET order and the boundary-bulk relation. This approach also leads us to a precise mathematical description and a classification of SPT/SET orders in all dimensions. The equivalence of these two approaches, together with known physical results, provides us with many precise mathematical predictions. We prove some of them rigorously.
Tue, 24 Mar 2020
- arXiv:2003.09421 [pdf, ps, other]
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Title: Mixture of scalar bosons and two-color fermions in one dimension: Superfluid-insulator transitionsComments: 9 pages, 5 figures, comments are welcomeSubjects: Quantum Gases (cond-mat.quant-gas); Quantum Physics (quant-ph)
Superfluid-insulator transitions in a one-dimensional mixture of two-color fermions and scalar bosons are studied within the framework of the Bose-Fermi-Hubbard model. Zero-temperature phase diagrams are constructed for repulsive intraspecies interactions and attractive or repulsive interspecies couplings. In addition to the trivial Mott insulator phases, we report the emergence of new non-trivial insulator phases that depend on the sign of the boson-fermion interaction. These non-trivial insulator phases satisfy the conditions $\rho_B\pm\rho_F=n$ and $\rho_B\pm \tfrac{1}{2}\rho_F=n$, with the plus (minus) sign for repulsive (attractive) interactions and $n$ an integer. Far from fermionic half-filling, the boson-fermion interaction drives a gapless-gapped transition in the spin sector. Our findings could be observed experimentally in state-of-the-art cold-atom setups.
- arXiv:2003.09423 [pdf, other]
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Title: Fractional and Integer Vortex Dynamics in Strongly Coupled Two-component Bose-Einstein Condensates from AdS/CFT CorrespondenceComments: 8 pages, 5 figuresSubjects: Quantum Gases (cond-mat.quant-gas); High Energy Physics - Theory (hep-th)
In order to study the rotating strongly coupled Bose-Einstein condensations(BEC), a holographic model defined in an AdS black hole that duals to a coupled two-component condensations in global $U(1)$ symmetry broken phase with intercomponent coupling $\eta$ and internal coherent coupling $\epsilon$ is proposed. By solving the dynamics of the model, we study the process of formation and also the crossover from fractional to integer vortex phases. With changing only $\eta$ from zero to a finite value, fractional vortex lattices undergo a transition from hexagon to square lattice and finally to vortex sheets. By continuing to turn on $\epsilon$, we find that two fractional vortices in different components constitute dimers, and when $\eta$ transcend a critical value, multi-dimer like hexamer or tetramer made up of two and three dimers appear. As $\epsilon$ keeps increasing, some dimers rotate to adjust themselves and then constitute the lattice of integer vortices. Under an initial conditions similar to an spinor BEC vortices dynamics experiment, the appearance of disordered turbulence is found in the process of fractional vortex generation, which matches the experimental observation. While in the formation process of integer vortices, the appearance of grooves is predicted.
- arXiv:2003.09425 [pdf, other]
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Title: From Föppl-von Kármán shells to enhanced one-dimensional rods: localization phenomena and multistabilitySubjects: Soft Condensed Matter (cond-mat.soft)
Starting from the F\"{o}ppl-von K\'{a}rm\'{a}n model of thin shells, we deduce two 1D models of elastic rods enhanced by additional kinematical descriptors that keep explicit track of the compatibility condition requested in the 2D parent continua, that in the classical rods models are identically satisfied after the dimensional reduction. These enhanced models allow to describe some phenomena of preeminent importance even in 1D bodies, such as formation of singularities and localization (d-cones), otherwise inaccessible by the classical 1D models. Moreover, the effects of the compatibility translate into the possibility to obtain multiple stable equilibrium configurations.
- arXiv:2003.09429 [pdf, ps, other]
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Title: Fracton hydrodynamicsComments: 7 + 5 pages. v2: minor revisions; references addedSubjects: Strongly Correlated Electrons (cond-mat.str-el); Statistical Mechanics (cond-mat.stat-mech); High Energy Physics - Theory (hep-th); Quantum Physics (quant-ph)
We introduce new classes of hydrodynamic theories inspired by the recently discovered fracton phases of quantum matter. Fracton phases are characterized by elementary excitations (fractons) with restricted mobility. The hydrodynamic theories we introduce describe thermalization in systems with fracton-like mobility constraints, including fluids where charge and dipole moment are both locally conserved, and fluids where charge is conserved along every line or plane of a lattice. Each of these fluids is subdiffusive, and constitutes a new universality class of hydrodynamic behavior. There are infinitely many such classes, each with distinct subdiffusive exponents, all of which are captured by our formalism. Our framework naturally explains recent results on dynamics with constrained quantum circuits, as well as recent experiments with ultracold atoms in tilted optical lattices. We identify crisp experimental signatures of these novel hydrodynamics, and explain how they may be realized in near term ultracold atom experiments.
- arXiv:2003.09430 [pdf, other]
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Title: Extracting many body localization lengths with an imaginary vector potentialSubjects: Disordered Systems and Neural Networks (cond-mat.dis-nn)
One challenge of studying the many-body localization transition is defining the length scale that diverges upon the transition to the ergodic phase. In this manuscript we explore the localization properties of a ring with onsite disorder subject to an imaginary magnetic flux. We connect the imaginary flux which delocalizes single-particle orbitals of an Anderson-localized ring with the localization length of an open chain. We thus identify the delocalizing imaginary flux per site with the inverse localization length. We put this intuition to use by exploring the phase diagram of a disordered interacting chain, and find that the inverse imaginary flux per bond provides an accessible description of the transition and its diverging localization length.
- arXiv:2003.09431 [pdf, other]
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Title: Normal state properties of quantum critical metals at finite temperatureSubjects: Strongly Correlated Electrons (cond-mat.str-el); Superconductivity (cond-mat.supr-con)
We study the effects of finite temperature on normal state properties of a metal near a quantum critical point to an antiferromagnetic or Ising-nematic state. At $T = 0$ bosonic and fermionic self-energies are traditionally computed within Eliashberg theory and obey scaling relations with characteristic power-laws. Quantum Monte Carlo (QMC) simulations have shown strong systematic deviations from these predictions, casting doubt on the validity of the theoretical analysis. We extend Eliashberg theory to finite $T$ and argue that for the $T$ range accessible in the QMC simulations, the scaling forms for both fermionic and bosonic self energies are quite different from those at $T = 0$. We compare finite $T$ results with QMC data and find good agreement for both systems. This, we argue, resolves the key apparent contradiction between the theory and the QMC simulations.
- arXiv:2003.09433 [pdf, other]
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Title: The two-dimensional electron self-energy: Long-range Coulomb interactionComments: 15 pages, 3 figuresSubjects: Strongly Correlated Electrons (cond-mat.str-el)
The electron self-energy for long-range Coulomb interactions plays a crucial role in understanding the many-body physics of interacting electron systems (e.g. in metals and semiconductors), and has been studied extensively for decades. In fact, it is among the oldest and the most-investigated many body problems in physics. However, there is a lack of an analytical expression for the self-energy $Re \Sigma^{(R)}( \varepsilon,T)$ when energy $\varepsilon$ and temperature $k_{B} T$ are arbitrary with respect to each other (while both being still small compared with the Fermi energy). We revisit this problem and calculate analytically the self-energy on the mass shell for a two-dimensional electron system with Coulomb interactions in the high density limit $r_s \ll 1$, for temperature $ r_s^{3/2} \ll k_{B} T/ E_F \ll r_s$ and energy $r_s^{3/2} \ll |\varepsilon |/E_F \ll r_s$. We provide the exact high-density analytical expressions for the real and imaginary parts of the electron self-energy with arbitrary value of $\varepsilon /k_{B} T$, to the leading order in the dimensionless Coulomb coupling constant $r_s$, and to several higher than leading orders in $k_{B} T/r_s E_F$ and $\varepsilon /r_s E_F$. We also obtain the asymptotic behavior of the self-energy in the regimes $|\varepsilon | \ll k_{B} T$ and $|\varepsilon | \gg k_{B} T$. The higher-order terms have subtle and highly non-trivial compound logarithmic contributions from both $\varepsilon $ and $T$, explaining why they have never before been calculated in spite of the importance of the subject matter.
- arXiv:2003.09455 [pdf, other]
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Title: Aqueous Nanoclusters Govern Ion Partitioning in Dense Polymer MembranesComments: 11 pages, 7 figuresJournal-ref: ACS Nano 2019, 13, 11224-11234Subjects: Soft Condensed Matter (cond-mat.soft)
The uptake and sorption of charged molecules by responsive polymer membranes and hydrogels in aqueous solutions is of key importance for the development of soft functional materials. Here we investigate the partitioning of simple monoatomic (Na$^+$, K$^+$, Cs$^+$, Cl$^-$, I$^-$) and one molecular ion (4-nitrophenolate; NP$^-$) within a dense, electroneutral poly($N$-isopropylacrylamide) membrane using explicit-water molecular dynamics simulations. Inside the predominantly hydrophobic environment water distributes in a network of polydisperse water nanoclusters. The average cluster size determines the mean electrostatic self-energy of the simple ions, which preferably reside deeply inside them; we therefore find substantially larger partition ratios $K\simeq\>$10$^{-1}$ than expected from a simple Born picture using a uniform dielectric constant. Despite their irregular shapes we observe that the water clusters possess a universal negative electrostatic potential with respect to their surrounding, as is known for aqueous liquid-vapor interfaces. This potential, which we find concealed in cases of symmetric monoatomic salts, can dramatically impact the transfer free energies of larger charged molecules because of their weak hydration and increased affinity to interfaces. Consequently, and in stark contrast to the simple ions, the molecular ion NP$^-$ can have a partition ratio much larger than unity, $K\simeq\>$10-30 (depending on the cation type) or even $10^3$ in excess of monovalent salt, which explains recent observations of enhanced reaction kinetics of NP$^-$ reduction catalyzed within dense polymer networks. These results also suggest that ionizing a molecule can even enhance the partitioning in a collapsed, rather hydrophobic gel, which strongly challenges the traditional simplistic reasoning.
- arXiv:2003.09462 [pdf, other]
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Title: Probing the Possibilities of Ergodicity in the 1D Spin-1/2 XY Chain with Quench DynamicsComments: 12 pages, 8 figuresJournal-ref: Scientific Reports, 10, 4407 (2020)Subjects: Quantum Physics (quant-ph); Strongly Correlated Electrons (cond-mat.str-el)
Ergodicity sits at the heart of the connection between statistical mechanics and dynamics of a physical system. By fixing the initial state of the system into the ground state of the Hamiltonian at zero temperature and tuning a control parameter, we consider the occurrence of the ergodicity with quench dynamics in the one-dimensional (1D) spin-1/2 XY model in a transverse magnetic field. The ground-state phase diagram consists of two ferromagnetic and paramagnetic phases. It is known the magnetization in this spin system is non-ergodic. We set up two different experiments as we call them single and double quenches and test the dynamics of the magnetization along the $Z$-axis and the spin-spin correlation function along the $X$-axis which are the order parameters of the zero-temperature phases . Our exact results reveal that for single quenches at zero-temperature, the ergodicity depends on the initial state and the order parameter. Interestingly on the other setup, a double quench on a cyclic path, ergodicity is completely broken for starting from the phase corresponding to the order parameter. Otherwise, it depends on the first quenched point, and the quench time $T$ when the model spent before a second quench in the way back which gives an ability to controlling the ergodicity in the system. Therefore, and contrary to expectations, in the mentioned model the ergodicity can be observed with probing quench dynamics at zero-temperature. Our results provide further insight into the zero-temperature dynamical behavior of quantum systems and their connections to the ergodicity phenomenon.
- arXiv:2003.09468 [pdf, other]
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Title: Accelerating Auxiliary-Field Quantum Monte Carlo Simulations of Solids with Graphical Processing UnitSubjects: Computational Physics (physics.comp-ph); Strongly Correlated Electrons (cond-mat.str-el); Chemical Physics (physics.chem-ph)
We outline how auxiliary-field quantum Monte Carlo (AFQMC) can leverage graphical processing units (GPUs) to accelerate the simulation of solid state sytems. By exploiting conservation of crystal momentum in the one- and two-electron integrals we show how to efficiently formulate the algorithm to best utilize current GPU architectures. We provide a detailed description of different optimization strategies and profile our implementation relative to standard approaches, demonstrating a factor of 40 speed up over a CPU implementation. With this increase in computational power we demonstrate the ability of AFQMC to systematically converge solid state calculations with respect to basis set and system size by computing the cohesive energy of Carbon in the diamond structure to within 0.02 eV of the experimental result.
- arXiv:2003.09474 [pdf, other]
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Title: Experimental and theoretical study of tracer diffusion in a series of (CoCrFeMn)$_{100-x}$Ni$_x$ alloysAuthors: Josua Kottke, Daniel Utt, Mathilde Laurent-Brocq, Adnan Fareed, Daniel Gaertner, Loic Perriere, Lukasz Rogal, Alexander Stukowski, Karsten Albe, Sergiy V. Divinski, Gerhard WildeComments: 16 pages; 10 figuresSubjects: Materials Science (cond-mat.mtrl-sci)
Tracer diffusion of all constituting elements is studied at various temperatures in a series of (CoCrFeMn)$_{100-x}$Ni$_x$ alloys with compositions ranging from pure Ni to the equiatomic CoCrFeMnNi high-entropy alloy. At a given homologous temperature, the measured tracer diffusion coefficients change non-monotonically along the transition from pure Ni to the concentrated alloys and finally to the equiatomic CoCrFeMnNi alloy. This is explained by atomistic Monte-Carlo simulations based on a modified embedded-atom potentials, which reveal that local heterogeneities of the atomic configurations around a vacancy cause correlation effects and induce significant deviations from predictions of the random alloy model.
- arXiv:2003.09482 [pdf]
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Title: Probing the wavefunctions of correlated states in magic angle grapheneComments: 5 pages, 4 figures plus supplementary informationSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Strongly Correlated Electrons (cond-mat.str-el)
Using scanning probe microscopy and spectroscopy, we explore the spatial symmetry of the electronic wavefunctions of twisted bilayer graphene at the "magic angle" of 1.1 degrees. This small twist angle leads to a long wavelength moir\'e unit cell on the order of 13 nm and the appearance of two flat bands. As the twist angle is decreased, correlation effects increase until they are maximized at the magic angle. At this angle, the wavefunctions at the charge neutrality point show only C2 symmetry due to the emergence of a charge ordered state. As the system is doped, the symmetry of the wavefunctions change at each commensurate filling of the moir\'e unit cell pointing to the correlated nature of the spin and valley degeneracy broken states.
- arXiv:2003.09489 [pdf, other]
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Title: T$_{d}$ to 1T$^{\prime}$ structural phase transition in WTe$_{2}$ Weyl semimetalComments: 6 pages, 3 figuresSubjects: Materials Science (cond-mat.mtrl-sci)
Elastic neutron scattering on a single crystal and powder X-ray diffraction measurements were carried out to investigate how the crystal structure evolves as a function of temperature in the Weyl semimetal WTe$_{2}$. A sharp transition from the low-temperature orthorhombic phase (T$_{d}$) to the high-temperature monoclinic phase (1T$^{\prime}$) was observed at ambient pressure in the single crystal near $\sim$565 K. Unlike in MoTe$_{2}$, the solid-solid transition from T$_{d}$ to 1T$^{\prime}$ occurs without the cell doubling of the intermediate T$_{d}^{*}$ phase with AABB (or ABBA) layer stacking. In powders however, the thermal transition from the T$_{d}$ to the 1T$^{\prime}$ phase is broadened and a two phase coexistence was observed until 700K, well above the structural transition.
- arXiv:2003.09498 [pdf, other]
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Title: Impurity-bound states as detectors of topological band structures revisitedSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Strongly Correlated Electrons (cond-mat.str-el)
Band structures of topological insulators are characterized by non-local topological invariants. Consequently, proposals for the experimental detection using local probes are rare. A recent paper [Slager et al., Phys. Rev. B 92, 085126 (2015)] has argued, based on theoretical results for a particular class of models, that insulators with topologically trivial and non-trivial band structures in two space dimensions display a qualitatively different response to point-like impurities. Here we present a comprehensive investigation of the impurity response of a large set of models of non-interacting electrons on the honeycomb lattice, driven insulating by either broken inversion, broken time reversal, broken $C_3$, or broken translation symmetry. These cases include Hofstadter bands, strain-induced pseudo-Landau levels and higher-order topological insulators. Our results confirm that for hopping models respecting the lattice symmetries, the response to a single impurity can indeed distinguish between trivial and non-trivial band topology. However, for modulated or inhomogeneous host systems we find that trivial states of matter can display an impurity response akin to that of topologically non-trivial states, and thus the diagnostic fails.
- arXiv:2003.09499 [pdf]
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Title: Pulsed Neutron Spectroscopy of Low Dimensional Magnets: Past, Present, and FutureComments: Paper to be published in a special issue of Journal of Physics Condensed Matter in honor of the late Professor Roger A. CowleySubjects: Strongly Correlated Electrons (cond-mat.str-el)
The early 1990s saw the first useful application of pulsed neutron spectroscopy to the study of excitations in low dimensional magnetic systems, with Roger Cowley as a key participant in important early experiments. Since that time the technique has blossomed as a powerful tool utilizing vastly improved neutron instrumentation coupled with more powerful pulsed sources. Here we review representative experiments illustrating some of the fascinating physics that has been revealed in quasi-one and two dimensional systems
- arXiv:2003.09513 [pdf, other]
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Title: Chiral SO(4) spin-charge density wave and degenerate topological superconductivity in magic-angle-twisted bilayer-grapheneAuthors: Chen Lu, Yongyou Zhang, Yu Zhang, Ming Zhang, Cheng-Cheng Liu, Zheng-Cheng Gu, Wei-Qiang Chen, Fan YangComments: Revised version with an Section: Overview added. 14.5 pages, 9 figures plus AppendixSubjects: Strongly Correlated Electrons (cond-mat.str-el)
Starting from a realistic extended Hubbard model for a $p_{x,y}$-orbital tight-binding model on the Honeycomb lattice, we perform a thorough investigation on the possible electron instabilities in the magic-angle-twisted bilayer-graphene near the van Hove (VH) dopings. Here we focus on the interplay between the SU(2)$\times$SU(2) and the $D_3$ symmetries. While the former leads to the degeneracy between the inter-valley SDW and CDW and that between the inter-valley singlet and triplet SCs, the latter leads to the degeneracy and competition among the three symmetry-related wave vectors of the DW orders, originating from the FS-nesting. The interplay between the two degeneracies leads to intriguing quantum states relevant to recent experiments, as revealed by our systematic RPA based calculations followed by a succeeding mean-field energy minimization for the ground state. At the SU(2)$\times$SU(2) symmetric point, the degenerate inter-valley SDW and CDW are mixed into a new state of matter dubbed as the chiral SO(4) spin-charge DW. This state simultaneously hosts three mutually perpendicular 4-component vectorial spin-charge DW orders with each adopting one wave vector. In the presence of a tiny inter-valley exchange interaction with coefficient $J_H\to 0^{-}$, a pure chiral SDW state is obtained. In the case of $J_H\to 0^{+}$, a nematic CDW order is accompanied by two SDW orders with equal amplitudes. This nematic CDW+SDW state possesses a stripy distribution of the charge density, consistent with the recent STM observations. On the aspect of SC, while the triplet $p+ip$ and singlet $d+id$ topological SCs are degenerate at $J_H=0$ near the VH dopings, the former (latter) is favored for $J_H\to 0^{-}$ ($J_H\to 0^{+}$). In addition, the two asymmetric doping-dependent behaviors of the superconducting Tc obtained are well consistent with experiments.
- arXiv:2003.09519 [pdf, ps, other]
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Title: Higher-dimensional generalizations of the Thouless charge pumpComments: 32 pagesSubjects: Strongly Correlated Electrons (cond-mat.str-el); High Energy Physics - Theory (hep-th); Mathematical Physics (math-ph)
We define and study analogs of the Thouless charge pump for many-body gapped systems in dimension $D$. We show how to attach a topological invariant to a $D$-dimensional family of such systems, provided all of them have an on-site $U(1)$ symmetry. For a large class of families we argue that this topological invariant is an integer. In the case of gapped systems of free fermions in two dimensions, the invariant can be expressed in terms of the curvature of the Bloch-Berry connection. We also obtain a new formula for the Thouless charge pump in 1d which involves only static linear response and is analogous to the Streda formula for Hall conductivity.
- arXiv:2003.09523 [pdf, other]
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Title: py4DSTEM: a software package for multimodal analysis of four-dimensional scanning transmission electron microscopy datasetsAuthors: Benjamin H Savitzky, Lauren A Hughes, Steven E Zeltmann, Hamish G Brown, Shiteng Zhao, Philipp M Pelz, Edward S Barnard, Jennifer Donohue, Luis Rangel DaCosta, Thomas C. Pekin, Ellis Kennedy, Matthew T Janish, Matthew M Schneider, Patrick Herring, Chirranjeevi Gopal, Abraham Anapolsky, Peter Ercius, Mary Scott, Jim Ciston, Andrew M Minor, Colin OphusComments: 32 pages, 18 figuresSubjects: Materials Science (cond-mat.mtrl-sci); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Applied Physics (physics.app-ph)
Scanning transmission electron microscopy (STEM) allows for imaging, diffraction, and spectroscopy of materials on length scales ranging from microns to atoms. By using a high-speed, direct electron detector, it is now possible to record a full 2D image of the diffracted electron beam at each probe position, typically a 2D grid of probe positions. These 4D-STEM datasets are rich in information, including signatures of the local structure, orientation, deformation, electromagnetic fields and other sample-dependent properties. However, extracting this information requires complex analysis pipelines, from data wrangling to calibration to analysis to visualization, all while maintaining robustness against imaging distortions and artifacts. In this paper, we present py4DSTEM, an analysis toolkit for measuring material properties from 4D-STEM datasets, written in the Python language and released with an open source license. We describe the algorithmic steps for dataset calibration and various 4D-STEM property measurements in detail, and present results from several experimental datasets. We have also implemented a simple and universal file format appropriate for electron microscopy data in py4DSTEM, which uses the open source HDF5 standard. We hope this tool will benefit the research community, helps to move the developing standards for data and computational methods in electron microscopy, and invite the community to contribute to this ongoing, fully open-source project.
- arXiv:2003.09538 [pdf]
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Title: Two-dimensional metallic ferroelectricity in PbTe monolayer by electrostatic dopingAuthors: Tao Xu (1), Jingtong Zhang (2), Yuquan Zhu (1), Jie Wang (2), Takahiro Shimada (3), Takayuki Kitamura (3), Tong-Yi Zhang (1) ((1) Materials Genome Institute, Shanghai University (2) Department of Engineering Mechanics, School of Aeronautics and Astronautics, Zhejiang University (3) Department of Mechanical Engineering and Science, Kyoto University)Comments: 17 pages, 4 figures,Subjects: Materials Science (cond-mat.mtrl-sci)
Polar metals characterized by the simultaneous coexistence of ferroelectric distortions and metallicity have attracted tremendous attention. Developing such materials at low dimensions remains challenging since both conducting electrons and reduced dimensions are supposed to quench ferroelectricity. Here, based on first-principles calculations, we report the discovery of ferroelectric behavior in two-dimensional (2D) metallic materials with electrostatic doping, even though ferroelectricity is unconventional at the atomic scale. We reveal that PbTe monolayer is intrinsic ferroelectrics with pronounced out-of-plane electric polarization originated from its non-centrosymmetric buckled structure. The ferroelectric distortions can be preserved with carriers doping in the ferroelectric monolayer, which thus enables the doped PbTe monolayer to act as a 2D polar metal. With an effective Hamiltonian extracted from the parametrized energy space, we found that the elastic-polar mode interaction is of great importance for the existence of robust polar instability in the doped system. The application of this doping strategy is not specific to the present crystal, but is rather general to other 2D ferroelectrics to bring about the fascinating metallic ferroelectric properties. Our findings thus change conventional acknowledge in 2D materials and will facilitate the development of multifunctional material in low dimensions.
- arXiv:2003.09560 [pdf]
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Title: Strain rate dependency of dislocation plasticityComments: 31 pages, 6 figures, 71 conferencesSubjects: Materials Science (cond-mat.mtrl-sci)
Dislocation slip is a general deformation mode and governs the strength of metals. Via discrete dislocation dynamics and molecular dynamics simulations, we investigate the strain rate and dislocation density dependence of the strength of bulk copper single crystals using 192 simulations spanning over 10 orders of magnitude in strain rate and 9 orders of magnitude in dislocation density. Based on these large set of simulations and theoretical analysis, a new analytical relationship between material strength, dislocation density, strain rate and dislocation mobility is proposed, which is in excellent agreement with the current simulations as well as with experimental data. The results show that the material strength is a non-monotonic function of dislocation density and displays two universal regimes (first decreasing, then increasing) as the dislocation density increases. The first regime is a result of strain rate hardening, while the second regime is dominated by the classical Taylor forest hardening. Accordingly, the strength displays universally, as a function of strain rate, a rate-independent regime at low strain rates (governed by forest hardening) followed by a rate hardening regime at high strain rates (governed by strain rate hardening). All the results can be captured by a single scaling function. Finally, the fluctuations of dislocation flow are analyzed in terms of the strain rate dependent distribution of dislocation segment velocities. It is found that the fluctuations are governed by another universal scaling function and diverge in the rate independent limit, indicating a critical behavior. The current analysis provides a comprehensive understanding on how collective dislocation motions are governed by the competition between the internal elastic interactions of dislocations, and the stress required to drive dislocation fluxes at a given externally imposed strain rate.
- arXiv:2003.09569 [pdf, ps, other]
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Title: Universal quantum reservoir computingSubjects: Quantum Physics (quant-ph); Disordered Systems and Neural Networks (cond-mat.dis-nn)
We show that quantum reservoir neural networks offer an alternative paradigm for universal quantum computing. In this framework, a dynamical random quantum network, called the quantum reservoir, is used as a quantum processor for performing operations on computational qubits. We show various quantum operations including a universal set of quantum gates, which can be obtained with a single quantum reservoir network with different tunnelling amplitudes between the reservoir and the qubits. The same platform can also implement non-unitary quantum gates, which are useful to simulate open quantum systems with tuneable parameters. We present a comprehensive analysis of the system using the fermionic path integral formalism.
- arXiv:2003.09582 [pdf, other]
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Title: Lasing in a coupled hybrid double quantum dot-resonator systemJournal-ref: Phys. Rev. B 101, 115135 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We theoretically investigate the possibility of lasing in an electromagnetic resonator coupled to a voltage-biased hybrid double quantum dot comprised of a double quantum dot tunnel coupled simultaneously to a normal metal and a superconducting lead. Using a unitary transformation, we derive a resonator-double quantum dot interaction Hamiltonian in the rotating-wave approximation which reveals the fact that lasing in this system is mediated by electron transitions between Andreev energy levels in the system's density of states. Moreover, by employing a Markovian master equation incorporating dissipation effects for the electronic and photonic degrees of freedom, we numerically calculate the steady-state reduced density matrix of the system from which we determine the average photon number and its statistics in the resonator in various parameter regimes. We find that at some appropriate parameter configurations, lasing can be considerably enhanced due to the possibility of electron transitions between multiple Andreev levels in the system.
- arXiv:2003.09590 [pdf, other]
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Title: Percolation between $k$ separated points in two dimensionsSubjects: Disordered Systems and Neural Networks (cond-mat.dis-nn); Statistical Mechanics (cond-mat.stat-mech)
We consider a percolation process in which $k$ widely separated points simultaneously connect together ($k>1$), or a single point at the center of a system connects to the boundary ($k=1$), through adjacent connected points of a single cluster. These processes yield new thresholds $\overline p_{ck}$ defined as the average value of $p$ at which the desired connections first occur. These thresholds are not sharp as the distribution of values of $p_{ck}$ remains broad in the limit of $L \to \infty$. We study $\overline p_{ck}$ for bond percolation on the square lattice, and find that $\overline p_{ck}$ are above the normal percolation threshold $p_c = 1/2$ and represent specific supercritical states. The $\overline p_{ck}$ can be related to integrals over powers of the function $P_\infty(p) =$ the probability a point is connected to the infinite cluster; we find numerically from both direct simulations and from measurements of $P_\infty(p)$ on $L\times L$ systems that for $L \to \infty$, $\overline p_{c1} = 0.51761(3)$, $\overline p_{c2} = 0.53220(3)$, $\overline p_{c3} = 0.54458(3)$, and $\overline p_{c4} = 0.55530(3)$. The percolation thresholds $\overline p_{ck}$ remain the same, even when the $k$ points are randomly selected within the lattice. We show that the finite-size corrections scale as $L^{-1/\nu_k}$ where $\nu_k = \nu/(k \beta +1)$, with $\beta=5/36$ and $\nu=4/3$ being the ordinary percolation critical exponents, so that $\nu_1= 48/41$, $\nu_2 = 24/23$, $\nu_3 = 16/17$, $\nu_4 = 6/7$, etc. We also study three-point correlations in the system, and show how for $p>p_c$, the correlation ratio goes to 1 (no net correlation) as $L \to \infty$, while at $p_c$ it reaches the known value of 1.021$\ldots.$
- arXiv:2003.09604 [pdf, other]
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Title: Quantum Potts Models on the Sierpiński PyramidAuthors: Roman Krčmár, Mária Zelenayová, Libor Caha, Peter Rapčan, Tomotoshi Nishino, Andrej GendiarComments: 4 pages, 3 figsSubjects: Statistical Mechanics (cond-mat.stat-mech); Computational Physics (physics.comp-ph)
Phase transition of the two- and three-state quantum Potts models on the Sierpi\'nski pyramid are studied by means of a tensor network framework, the higher-order tensor renormalization group method. Critical values of the transverse magnetic field and the magnetic exponent $\beta$ are evaluated. Despite the fact that the Hausdorff dimension of the Sierpi\'nski pyramid is exactly two $( = \log_2^{~} 4)$, the obtained critical properties show that the effective dimension is lower than two.
- arXiv:2003.09605 [pdf, other]
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Title: Spectrally tunable, large Raman enhancement from nonradiative energy transfer in van der Waals heterostructureJournal-ref: ACS Photonics, 7, 519, 2020Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci)
Raman enhancement techniques are essential for fundamental studies in light-matter interactions and find widespread application in microelectronics, bio-chemical sensing, and clinical diagnosis. Two-dimensional (2D) materials and their van der Waals heterostructures (vdWHs) are emerging rapidly as potential platforms for Raman enhancement. Here, we experimentally demonstrate a new technique of Raman enhancement driven by nonradiative energy transfer (NRET) achieving a $10$-fold enhancement in the Raman intensity in a vertical vdWH comprising of a monolayer transition metal dichalcogenide (1L-TMD) placed on a multilayer SnSe\tsub2. Consequently, several weak Raman peaks become visible which are otherwise imperceptible. We also show a strong modulation of the enhancement factor by tuning the spectral overlap between the 1L-TMD and SnSe\tsub2 through temperature variation and the results are in remarkable agreement with a Raman polarizability model capturing the effect of NRET. The observed NRET driven Raman enhancement is a novel mechanism which has not been experimentally demonstrated thus far and is distinct from conventional surface (SERS), tip (TERS) or Interference enhanced Raman scattering (IERS) mechanisms that are driven solely by charge transfer or electric field enhancement. The mechanism can also be used in synergy with plasmonic nanostructures to achieve additional selectivity and sensitivity beyond hot spot engineering for applications like molecular detection using 2D/molecular hybrids. Our results open new avenues for engineering Raman enhancement techniques coupling the advantages of uniform enhancement accessible across a wide junction area in vertical vdWHs.
- arXiv:2003.09607 [pdf, ps, other]
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Title: Unidirectional ripplopolaron charge transport in a three-terminal microchannel deviceComments: 5 pages, 3 figuresJournal-ref: Phys. Rev. Lett. 124, 126803 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We study the transport of surface electrons on superfluid helium through a microchannel structure in which the charge flow splits into two branches, one flowing straight and one turned at 90 degrees. According to Ohm law, an equal number of charges should flow into each branch. However, when the electrons are dressed by surface excitations (ripplons) to form polaron-like particles with sufficiently large effective mass, all the charge follows the straight path due to momentum conservation. This surface-wave induced transport is analogous to the motion of electrons coupled to surface acoustic waves in semiconductor 2DEGs.
- arXiv:2003.09611 [pdf]
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Title: Induced Ferromagnetism in bilayer Hexagonal Boron Nitride (h-BN) on vacancy defects at B and N sitesAuthors: B. Chettri, P. K. Patra, Tuan V. Vu, Lalrinkima, Abu Yaya, Kingsley O. Obodo, Ngoc Thanh Thuy Tran, A. Laref, D. P. RaiSubjects: Materials Science (cond-mat.mtrl-sci); Disordered Systems and Neural Networks (cond-mat.dis-nn)
We investigated the electronic and optical properties of bilayer AB stacked Boron and Nitrogen vacancies in hexagonal Boron Nitride (h-BN) using density functional theory (DFT). The density of states (DOS) and electronic band structure showed that Boron vacancy in bilayer h-BN results in a magnetic and conducting ground state. The band gap energy ranges from 4.56 eV for the pristine BN bilayer to 0.12 eV for a single Nitrogen vacancy in the bilayer. Considering the presence of 1,3,4-Boron vacancy, half metallic character is observed. However, the 2-boron vacancy configuration resulted in metallic character. The bilayers with 1,2,3,4- Nitrogen vacancy has a band gap of 0.39, 0.33, 0.28 and 0.12eV respectively, which is significantly less than the pristine band gap. Also B and N vacancy induces ferromagnetism in the h-BN bilayer. The maximum total magnetic moment for the Boron vacant system is 6.583uB in case of 4-Boron vacancy configuration. In case of Nitrogen vacancy system it is 3.926uB for 4-Nitrogen vacancy configuration. The optical response of the system is presented in terms of the absorption coefficient, refractive index and dielectric constant for pristine as well as the defective configurations. Negative value of dielectric constant for Boron vacant system in the energy range 0.9-1.4 eV and for Nitrogen vacant system in the energy range 0.5-0.8 eV opens an opportunity for it to be utilized for negative index optical materials. The current study shows that B and N vacancies in bilayer h-BN could have potential applications in nano-structure based electronics, optoelectronics and spintronic devices.
- arXiv:2003.09612 [pdf]
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Title: Evidence of tunable magnetic coupling in hydrogenated grapheneSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
A lot of efforts have been devoted to understanding the origin and effects of magnetic moments induced in graphene with carbon atom vacancy, or light adatoms like hydrogen or fluorine. At the meantime, the large negative magnetoresistance (MR) widely observed in these systems is not well understood, nor had it been associated with the presence of magnetic moments. In this paper, we study the systematic evolution of the large negative MR of in-situ hydrogenated graphene in ultra-high vacuum (UHV) environment. We find for most combination of electron density ($n_e$) and hydrogen density ($n_H$), MR at different temperature can be scaled to $\alpha=(\mu_BB)/[k_B(T-T^*)]$, where $T^*$ is the Curie-Weiss temperature. The sign of $T^*$ indicates the existence of tunable ferromagnetic-like ($T^* >0$) and anti-ferromagnetic-like ($T^* <0$) coupling in hydrogenated graphene. However, the lack of hysteresis of MR or anomalous Hall effect below $|T^*|$ points to the fact that long-range magnetic order did not emerge, which we attribute to the competition of different magnetic orders and disordered arrangement of magnetic moments on graphene. We also find that localized impurity states introduced by H adatoms could modify the capacitance of hydrogenated graphene. This work provides a new way to extract information from large negative MR behavior and can be a key to help understanding interactions of magnetic moments in graphene.
- arXiv:2003.09614 [pdf, ps, other]
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Title: Non-thermal vibrations in biased molecular junctionsSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We study vibrational statistics in current-carrying model molecular junctions using master equation approach. Especially, we concentrate on the validity of using an effective temperature $T_{\rm eff}$ to characterize the nonequilibrium steady state of a vibrational mode. We identify cases where a single $T_{\rm eff}$ can not fully describe one vibrational state. In such cases, the probability distribution among different vibrational states does not follow the Boltzmann type. Consequently, the actual entropy (free energy) of the vibrational mode is lower (higher) than the corresponding thermal value given by $T_{\rm eff}$, indicating extra work can be extracted from these states. Our results will be useful for the study of non-thermal vibrational state in thermodynamics of nanoscale systems, and its usage in nanoscale heat engines.
- arXiv:2003.09622 [pdf]
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Title: Conductance switching at the nanoscale of diarylethene derivatives self-assembled monolayers on La$_{0.7}$Sr$_{0.3}$MnO$_3$Authors: L. Thomas, D. Guerin, B. Quinard, E. Jacquet, R. Mattana, P. Seneor, D. Vuillaume, T. Melin, S. LenfantComments: Full paper with supporting informationSubjects: Applied Physics (physics.app-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We report on the phosphonic acid route for the grafting of functional molecules, optical switch (dithienylethene diphosphonic acid, DDA), on La0.7Sr0.3MnO3 (LSMO). Compact self-assembled monolayers (SAMs) of DDA are formed on LSMO as studied by topographic atomic force microscopy (AFM), ellipsometry, water contact angle and X-ray photoemission spectroscopy (XPS). The conducting AFM measurements show that the electrical conductance of LSMO/DDA is about 3 decades below that of the bare LSMO substrate. Moreover, the presence of the DDA SAM suppresses the known conductance switching of the LSMO substrate that is induced by mechanical and/or bias constraints during C-AFM measurements. A partial light-induced conductance switching between the open and closed forms of the DDA is observed for the LSMO/DDA/C-AFM tip molecular junctions (closed/open conductance ratio of about 8). We show that, in the case of long-time exposition to UV light, this feature can be masked by a non-reversible decrease (a factor of about 15) of the conductance of the LSMO electrode.
- arXiv:2003.09627 [pdf, other]
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Title: Secondary relaxation in the terahertz range in 2-adamantanone from theory and experimentsAuthors: Bingyu Cui, Jonathan F. Gebbia, Michela Romanini, Svemir Rudić, Ricardo Fernandez-Perea, F. Javier Bermejo, Josep-Lluis Tamarit, Alessio ZacconeJournal-ref: Phys. Rev. B 101, 104202 (2020)Subjects: Soft Condensed Matter (cond-mat.soft); Disordered Systems and Neural Networks (cond-mat.dis-nn); Materials Science (cond-mat.mtrl-sci)
We applied the recently developed Generalized Langevin Equation (GLE) approach for dielectric response of liquids and glasses to link the vibrational density of states (VDOS) to the dielectric response of a model orientational glass (OG). The dielectric functions calculated based on the GLE, with VDOS obtained in experiments and simulations as inputs, are compared with experimental data for the paradigmatic case of 2-adamantanone at various temperatures. The memory function is related to the integral of the VDOS times a spectral coupling function $\gamma(\omega_p)$, which tells the degree of dynamical coupling between molecular degrees of freedom at different eigenfrequencies. With respect to previous empirical fittings, the GLE-based fitting reveals a broader temperature range over which the secondary relaxation is active. Furthermore, the theoretical analysis provides a clear evidence of secondary relaxation being localized within the THz ($0.5-1$ THz) range of eigenfrequencies, and thus not too far from the low-energy modes involved in $\alpha$-relaxation. In the same THz region, the same material displays a crowding of low-energy optical modes that may be related to the secondary relaxation.
- arXiv:2003.09629 [pdf, other]
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Title: Anomalous dynamics in the ergodic side of the Many-Body Localization transition and the glassy phase of Directed Polymers in Random MediaComments: text 14 pages, Appendix 4 pagesSubjects: Disordered Systems and Neural Networks (cond-mat.dis-nn); Statistical Mechanics (cond-mat.stat-mech); Quantum Physics (quant-ph)
Using the non-interacting Anderson tight-binding model on the Bethe lattice as a toy model for the many-body quantum dynamics, we propose a novel and transparent theoretical explanation of the anomalously slow dynamics that emerges in the bad metal phase preceding the Many-Body Localization transition. By mapping the time-decorrelation of many-body wave-functions onto Directed Polymers in Random Media, we show the existence of a glass transition within the extended regime separating a metallic-like phase at small disorder, where delocalization occurs on an exponential number of paths, from a bad metal-like phase at intermediate disorder, where resonances are formed on rare, specific, disorder dependent site orbitals on very distant generations. The physical interpretation of subdiffusion and non-exponential relaxation emerging from this picture is complementary to the Griffiths one, although both scenarios rely on the presence of heavy-tailed distribution of the escape times. We relate the dynamical evolution in the glassy phase to the depinning transition of Directed Polymers, which results in macroscopic and abrupt jumps of the preferred delocalizing paths when a parameter like the energy is varied, and produce a singular behavior of the overlap correlation function between eigenstates at different energies. By comparing the quantum dynamics on loop-less Cayley trees and Random Regular Graphs we discuss the effect of loops, showing that in the latter slow dynamics and apparent power-laws extend on a very large time-window but are eventually cut-off on a time-scale that diverges at the MBL transition.
- arXiv:2003.09634 [pdf, other]
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Title: Spectral Design of Active Mechanical and Electrical MetamaterialsComments: 3 pages, 2 figures. Submitted to "14$^{th}$ International Congress on Artificial Materials for Novel Wave Phenomena - Metamaterials 2020"Subjects: Applied Physics (physics.app-ph); Materials Science (cond-mat.mtrl-sci)
Active matter is ubiquitous in biology and becomes increasingly more important in materials science. While numerous active systems have been investigated in detail both experimentally and theoretically, general design principles for functional active materials are still lacking. Building on a recently developed linear response optimization (LRO) framework, we here demonstrate that the spectra of nonlinear active mechanical and electric circuits can be designed similarly to those of linear passive networks.
- arXiv:2003.09645 [pdf, other]
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Title: Competition of Pairing and Nematicity in the Two-Dimensional Electron GasJournal-ref: Annu. Rev. Cond. Mat. Phys. 11, 17 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Due to its extremely rich phase diagram, the two-dimensional electron gas exposed to perpendicular magnetic field has been the subject of intense and sustained study. One particularly interesting problem in this system is that of the half-filled Landau level, where the Fermi sea of composite fermions, a fractional quantum Hall state arising from a pairing instability of the composite fermions, and the quantum Hall nematic were observed in the half-filled $N=0$, $N=1$, and $N \geq 2$ Landau levels, respectively. Thus different ground states developed in different half-filled Landau levels. This situation has recently changed, when evidence for both the paired fractional quantum Hall state and the quantum Hall nematic was reported in the half-filled $N=1$ Landau level. Furthermore, a direct quantum phase transition between these two ordered states was found. These results highlight an intimate connection between pairing and nematicity, a topic of current interest in several strongly correlated systems, in a well-understood and low disorder environment.
- arXiv:2003.09649 [pdf, other]
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Title: Room Temperature Amplification of Terahertz Radiation by Grating-Gate Graphene StructuresAuthors: Stephane Boubanga-Tombet, Wojciech Knap, Deepika Yadav, Akira Satou, Dmytro B. But, Vyacheslav V. Popov, Ilya V. Gorbenko, Valentin Kachorovskii, Taiichi OtsujiComments: 17 pages with 15 figures, uses revtex4-2, additionally include 6 pages of supplementary materials with 6 figuresSubjects: Applied Physics (physics.app-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We report on experimental studies of terahertz (THz) radiation transmission through grating-gate graphene-channel transistor nanostructures and demonstrate room temperature THz radiation amplification stimulated by current-driven plasmon excitations. Specifically, with increase of the direct current (dc) under periodic charge density modulation, we observe a strong red shift of the resonant THz plasmon absorption, its complete bleaching, followed by the amplification and blue shift of the resonant plasmon frequency. Our results are, to the best of our knowledge, the first experimental observation of energy transfer from dc current to plasmons leading to THz amplification. We present a simple model allowing for the phenomenological description of the observed amplification phenomena. This model shows that in the presence of dc current the radiation-induced correction to dissipation is sensitive to the phase shift between THz oscillations of carrier density and drift velocity, and with increase of the current becomes negative, leading to amplification. The experimental results of this work as all obtained at room temperature, pave the way towards the new 2D plasmons based, voltage tuneable THz radiation amplifiers.
- arXiv:2003.09652 [pdf, ps, other]
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Title: Temperature dependence of the order parameter of the polar phase of liquid 3He in nematic aerogelAuthors: I. A. FominComments: 8 pages, submitted to JETPSubjects: Disordered Systems and Neural Networks (cond-mat.dis-nn); Other Condensed Matter (cond-mat.other)
It is shown that in the polar phase of superfluid 3 He, stabilized by nematic aerogel, at the condition of specular reflection of quasi-particles from the strands of aerogel the temperature dependence of the gap in the spectrum of quasi-particles coincides with that in the bulk polar phase without impurities. The analogy with the Anderson theorem for conventional superconductors is discussed.
- arXiv:2003.09653 [pdf, other]
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Title: Non-equilibrium Properties of Berezinskii-Kosterlitz-Thouless Phase TransitionsSubjects: Strongly Correlated Electrons (cond-mat.str-el)
We employ a novel, unbiased renormalization-group approach to investigate non-equilibrium phase transitions in infinite lattice models. This allows us to address the delicate interplay of fluctuations and ordering tendencies in low dimensions. We study a prototypical model of spinless interacting fermions coupled to electronic baths and driven out of equilibrium by a longitudinal electric field. The closed system features a Berezinskii-Kosterlitz-Thouless transition between a metallic and a charge-ordered phase in the equilibrium limit. We compute the non-equilibrium phase diagram and illustrate a highly non-monotonic dependence of the phase boundary on the strength of the electric field: For small fields, the induced currents destroy the charge order, while at higher electric fields it reemerges due to many-body Wannier-Stark localization physics. Finally, we show that the current in such an interacting non-equilibrium system can counter-intuitively flow opposite to the direction of the electric field. This non-equilibrium steady-state is reminiscent of an equilibrium distribution function with an effective negative temperature.
- arXiv:2003.09654 [pdf, other]
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Title: Phases of translation-invariant systems out of equilibrium: Iterative Green's function techniques and renormalization group approachesSubjects: Strongly Correlated Electrons (cond-mat.str-el)
We introduce a method to evaluate the steady-state non-equilibrium Keldysh-Schwinger Green's functions for infinite systems subject to both an electric field and a coupling to reservoirs. The method we present exploits a physical quasi-translation invariance, where a shift by one unit cell leaves the physics invariant if all electronic energies are simultaneously shifted by the magnitude of the electric field. Our framework is straightaway applicable to diagrammatic many-body methods. We discuss two flagship applications, mean-field theories as well as a sophisticated second-order functional renormalization group approach. The latter allows us to push the renormalization-group characterization of phase transitions for lattice fermions into the out-of-equilibrium realm. We exemplify this by studying a model of spinless fermions, which in equilibrium exhibits a Berezinskii-Kosterlitz-Thouless phase transition.
- arXiv:2003.09657 [pdf, other]
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Title: Magnetic breakdown and charge density wave formation: a quantum oscillation study of the rare-earth tritelluridesAuthors: P. Walmsley, S. Aeschlimann, J. A. W. Straquadine, P. Giraldo-Gallo, S. C. Riggs, M. K. Chan, R. D. McDonald, I. R. FisherComments: 11 pages, 7 figuresSubjects: Strongly Correlated Electrons (cond-mat.str-el)
The rare-earth tritellurides ($R$Te$_3$, where $R$ = La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Y) form a charge density wave state consisting of a single unidirectional charge density wave for lighter $R$, with a second unidirectional charge density wave, perpendicular and in addition to the first, also present at low temperatures for heavier $R$. We present a quantum oscillation study in magnetic fields up to 65T that compares the single charge density wave state with the double charge density wave state both above and below the magnetic breakdown field of the second charge density wave. In the double charge density wave state it is observed that there remain several small, light pockets with the largest occupying around 0.5% of the Brillouin zone. By applying magnetic fields above the independently determined magnetic breakown field, the quantum oscillation frequencies of the single charge density wave state are recovered, as expected in a magnetic breakdown scenario. Measurements of the electronic effective mass do not show any divergence or significant increase on the pockets of Fermi surface observed here as the putative quantum phase transition between the single and double charge density wave states is approached.
- arXiv:2003.09665 [pdf]
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Title: Premelting fluctuationsAuthors: Pavel GolovinskiSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Applied Physics (physics.app-ph)
A model of the premelting fluctuations is proposed, based on the Landau mean field theory applied to a first-order phase transition. Using the thermodynamic potential, the nonlinear Langevin equation for the order parameter is formulated, which describes the dynamics of the phase transition considering microscopic thermal fluctuations. The origin of the low-frequency fluctuations, associated with a switching in a bistable system under the influence of a thermal noise, is shown. Analytical two-scale model of the premelting fluctuations is developed, with characteristic frequent small-amplitude fluctuations of chaotic motion in the vicinity of potential minima and rarer large fluctuations due to solid-liquid transitions. Based on the numerical simulation of the solutions to the stochastic differential equation, both the dynamics of the order parameter fluctuations and their spectrum are obtained. The model qualitatively reproduces experimental spectrum of isothermal fluctuations.
- arXiv:2003.09674 [pdf, other]
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Title: Prediction of group IV-V hexagonal binary monolayers: electronic, optical, thermoelectric, and photocatalysis propertiesAuthors: Mohammad Ali Mohebpour, Shobair Mohammadi Mozvashi, Sahar Izadi Vishkayi, Meysam Bagheri TaganiComments: 18 pages, 14 FigsSubjects: Materials Science (cond-mat.mtrl-sci); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Group IV and V monolayers are very crucial 2D materials for their high carrier mobilities, tunable band gaps, and optical linear dichroism. Very recently, a novel group IV-V binary compound, Sn2Bi, has been synthesized on silicon substrate, and has shown very interesting electronic and thermoelectric properties. Further investigations show that show that the monolayer would be stable in freestanding form by hydrogenation. Inspired by this, by means of ab-initio calculations, we systematically predict and investigate eight counterparts of Sn2Bi, namely Si2P, Si2As, Si2Sb, Si2Bi, Ge2P, Ge2As, Ge2Sb, and Ge2Bi. The cohesive energies, phonon dispersions, and AIMD calculations show that, similar to Sn2Bi, all of these freestanding monolayers are stable when they are hydrogenated. These hydrogenated monolayers are semiconductors with wide band gaps, which are favorable for opto-electronic purposes. The Si2Y and Ge2Y structures possess indirect and direct band gaps, respectively. They represent very interesting optical characteristics, such as good absorption in the visible region and linear dichroism, which are crucial for solar cell and beam-splitting devices, respectively. Moreover, the Ge2P and Si2Sb monolayers are promising for highspeed nano-electronic devices, because of their high carrier mobility, whereas Si2Bi, Ge2P, and Si2As monolayers are suitable candidates for thermoelectricity. Finally, the Si2Sb and Si2Bi monolayers have suitable band gaps and band edge positions for photocatalytic water splitting. Summarily, our investigations offer very interesting and promising properties for this family of binary compounds. We hope that our predictions open ways to new experimental studies and fabrication of suitable 2D materials for next generation opto-electronic, thermoelectric, and photocatalytic devices.
- arXiv:2003.09678 [pdf, ps, other]
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Title: Comment on "Berezinskii-Kosterlitz-Thouless transition in two-dimensional dipolar stripes"Comments: 3 pages, submitted as a comment to Physical Review ASubjects: Quantum Gases (cond-mat.quant-gas)
In a recent article [R. Bombin, F. Mazzanti and J. Boronat, Phys. Rev. A 100, 063614 (2019)], it is contended that a two-dimensional system of dipolar bosons, with dipole moments aligned at particular angles with respect to the direction perpendicular to the plane of motion, featuring a "striped" crystalline ground state, in turn undergoes a Berezinskii-Kosterlitz-Thouless superfluid transition at low temperature, making it a two-dimensional supersolid. We show here that the results provided therein, obtained by means of Quantum Monte Carlo simulations, do not actually support such a conclusion. Rather, they are consistent with that expounded in our work [J. Low Temp. Phys. 196, 413 (2019)], namely that the striped ground state is insulating (i.e., non-superfluid in the conventional sense), essentially behaving like a system of quasi-one-dimensional, parallel independent chains. We attribute the incorrectness of the conclusion reached by Bombin et al. to the very small sizes of their simulated system, which do not allow for a reliable extrapolation to the thermodynamic limit.
- arXiv:2003.09685 [pdf, ps, other]
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Title: Algorithms for Brownian dynamics across discontinuitiesAuthors: Oded FaragoSubjects: Statistical Mechanics (cond-mat.stat-mech); Computational Physics (physics.comp-ph)
The problem of mass diffusion in layered systems has relevance to applications in different scientific disciplines, e.g., chemistry, material science, soil science, and biomedical engineering. The mathematical challenge in these type of model systems is to match the solutions of the time-dependent diffusion equation in each layer, such that the boundary conditions at the interfaces between them are satisfied. As the number of layers increases, the solutions may become increasingly complicated. Here, we describe an alternative computational approach to multi-layer diffusion problems, which is based on the description of the overdamped Brownian motion of particles via the underdamped Langevin equation. In this approach, the probability distribution function is computed from the statistics of an ensemble of independent single particle trajectories. To allow for simulations of Langevin dynamics in layered systems, the numerical integrator must be supplemented with algorithms for the transitions across the discontinuous interfaces. Algorithms for three common types of discontinuities are presented: (i) A discontinuity in the friction coefficient, (ii) a semi-permeable membrane, and (iii) a step-function chemical potential. The general case of an interface where all three discontinuities are present (Kedem-Katchalsky boundary) is also discussed. We demonstrate the validity and accuracy of the derived algorithms by considering a simple two-layer model system and comparing the Langevin dynamics statistics with analytical solutions and alternative computational results.
- arXiv:2003.09688 [pdf, other]
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Title: Noise representations of open system dynamicsComments: ver 2: Fixed typos; minor cosmetic changes to Sec. 6 Conclusions; refined argumentation in Sec. 4.3 Environment of least actionSubjects: Quantum Physics (quant-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We analyze the conditions under which the dynamics of a quantum system open to a given environment can be simulated with an external noisy field that is a surrogate for the environmental degrees of freedom. We show that such a field is either a subjective or an objective surrogate; the former is capable of simulating the dynamics only for the specific system--environment arrangement, while the latter is an universal simulator for any system interacting with the given environment. Consequently, whether the objective surrogate field exists and what are its properties is determined exclusively by the environment. Thus, we are able to formulate the sufficient criterion for the environment to facilitate its surrogate, and we identify a number of environment types that satisfy it. Finally, we discuss in what sense the objective surrogate field representation can be considered classical and we explain its relation with the formation of system--environment entanglement, the back-action exerted by the system onto environment, and the Gaussian approximation to the system dynamics.
- arXiv:2003.09692 [pdf, other]
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Title: Origin of selective enhancement of sharp defect emission lines in monolayer WSe$_2$ on rough metal substrateJournal-ref: Journal of Applied Physics 127, 073105 (2020)Subjects: Applied Physics (physics.app-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
The defect states in atomically thin layers of transition metal dichalcogenides are promising candidates for single photon emission. However, the brightness of such quantum emission is often weak, and is accompanied with undesirable effects like spectral diffusion and strong background emission. By placing a monolayer WSe$_2$ directly on a rough gold substrate, here we show a selective enhancement of sharp defect-bound exciton peaks, coupled with a suppressed spectral diffusion and strong quenching of background luminescence. By combining the experimental data with detailed electromagnetic simulations, we reveal that such selective luminescence enhancement originates from a combination of the Purcell effect and a wavelength dependent increment of the excitation electric field at the tips of tall rough features, coupled with a localized strain induced exciton funneling effect. Notably, insertion of a thin hexagonal Boron Nitride (hBN) sandwich layer between WSe$_2$ and the Au film results in a strong enhancement of the background luminescence, obscuring the sharp defect peaks. The findings demonstrate a simple strategy of using monolayer WSe$_2$ supported by thin metal film that offers a possibility of achieving quantum light sources with high purity, high brightness, and suppressed spectral diffusion.
- arXiv:2003.09706 [pdf]
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Title: Azimuthal and polar anchoring energies of aligning layers structured by nonlinear laser lithographyAuthors: I. Pavlov, O. Candemir, A. Rybak, A. Dobrovolskiy, V. Kadan, I. Blonskyi, P. Lytvyn, A. Korchovyi, P. Tytarenko, Z. Kazantseva, I. GvozdovskyyComments: 49 pages, 18 figuresSubjects: Applied Physics (physics.app-ph); Soft Condensed Matter (cond-mat.soft)
In spite of the fact that there are different techniques in the creation of the high-quality liquid crystals (LCs) alignment by means of various surfaces, the azimuthal and polar anchoring energies as well as the pre-tilt angle are important parameters to all of them. Here, the modified by a certain manner aligning layers, previously formed by nonlinear laser lithography (NLL), having high-quality nano-periodic grooves on Ti surfaces, recently proposed for LC alignment was studied. The change of the scanning speed of NLL in the process of nano-structured Ti surfaces and their further modification by means of ITO-coating, and deposition of polyimide film has enabled different aligning layers, whose main characteristics, namely azimuthal and polar anchoring energies, were measured. For the modified aligning layers, the dependencies of the twist and pre-tilt angles for LC cells filled by nematic E7 ({\Delta}{\epsilon} > 0) and MLC-6609 ({\Delta}{\epsilon} < 0) were obtained. Also the contact angle for droplets of isotropic liquid (glycerol), and nematic LCs was measured for the various values of the scanning speed during the laser processing.
- arXiv:2003.09730 [pdf, other]
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Title: Ultra-low effective interfacial tension between miscible molecular fluidsComments: 11 pages, 6 figuresSubjects: Soft Condensed Matter (cond-mat.soft); Fluid Dynamics (physics.flu-dyn)
We exploit the deformation of drops spinning in a denser background fluid to investigate the effective interfacial tension (EIT) between miscible molecular fluids. We find that for sufficiently low interfacial tension, spinning drops develop dumbbell shapes, with two large heads connected by a thinner central body. We show that this shape depends not only on the density and viscosity contrast between the drop and background fluids, but also on the fluid molecular structure, and hence on the stresses developing at their interface due to different molecular interaction. We systematically investigate the dynamics of dumbbell-shaped drops of water-glycerol mixtures spinning in a pure glycerol reservoir. By developing a model for the deformation based on the balance of the shear stress opposing the deformation, the imposed normal stress on the drop and an effective interfacial tension, we exploit the time evolution of the drop shape to measure the EIT. Our results show that the EIT in water-glycerol systems is orders of magnitude lower than that reported in previous experimental measurements, and in excellent agreement with values calculated via the phase field model proposed in [Phys. Rev. X 6, 041057, 2016].
- arXiv:2003.09735 [pdf, ps, other]
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Title: A first-principles perspective on the magnetic second soundComments: 18 pages with color figuresSubjects: Strongly Correlated Electrons (cond-mat.str-el); Materials Science (cond-mat.mtrl-sci)
The fluctuations of the magnetic order parameter, or longitudinal spin excitations, are investigated theoretically in the ferromagnetic Fe and Ni as well as in the antiferromagnetic phase of the pnictide superconductor FeSe. The charge and spin dynamics of these systems is described by evaluating the generalized charge and spin density response function calculated from first-principles linear response time dependent density functional theory within adiabatic local spin density approximation. We observe that the formally non-interacting Kohn-Sham system features strong coupling between the magnetization and charge dynamics in the longitudinal channel and that the coupling is effectively removed upon the inclusion of the Coulomb interaction in the charge channel and the resulting appearance of plasmons. The longitudinal spin fluctuations acquire a collective character without the emergence of the Goldstone boson, similar to the case of paramagnon excitations in non-magnetic metals like Pd. In ferromagnetic Fe and Ni the longitudinal spin dynamics is governed by interactions between low-energy intraband electron-hole pairs while in quasi two dimensional antiferromagnet FeSe it is dominated by the interband transitions with energies of the order of exchange splitting. In the later material, the collective longitudinal magnetization fluctuations feature well defined energies and long life times for small momenta and appear below the particle-hole continuum. The modes become strongly Landau-damped for growing wave-vectors.
- arXiv:2003.09743 [pdf, other]
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Title: Low-temperature asymptotic of the transverse dynamical structure factor for a magnetically polarized XX chainAuthors: P.N. BibikovComments: 32 pages, 6 figuresSubjects: Strongly Correlated Electrons (cond-mat.str-el)
Dyson equation for the real two-time commutator retarded one-magnon Green function of the ferromagnetically polarized XX chain is suggested following the Plakida-Tserkovnikov algorithm. Starting from this result a low-temperature integral representation for the corresponding magnon self energy is obtained by the truncated form factor expansion however without any resummations. Within the suggested approach the low-temperature asymptotics of the transverse dynamical structure factor may be readily studied. Some obtained line shapes are presented.
- arXiv:2003.09745 [pdf, other]
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Title: Solid-solid phase equilibria in the NaCl-KCl systemComments: 10 pages, 9 figuresJournal-ref: Journal of Chemical Physics 152, 144109 (2020)Subjects: Statistical Mechanics (cond-mat.stat-mech); Materials Science (cond-mat.mtrl-sci); Computational Physics (physics.comp-ph)
Solid solutions, structurally ordered but compositionally disordered mixtures, can form for salts, metals, and even organic compounds. The NaCl-KCl system forms a solid solution at all compositions between 657{\deg}C and 505{\deg}C. Below a critical temperature of 505{\deg}C, the system exhibits a miscibility gap with coexisting Na-rich and K-rich rocksalt phases. We calculate the phase diagram in this region using the semi-grand canonical Widom method, which averages over virtual particle transmutations. We verify our results by comparison with free energies calculated from thermodynamic integration and extrapolate the location of the critical point. The calculations reproduce the experimental phase diagram remarkably well and illustrate how solid-solid equilibria and chemical potentials, including those at metastable conditions, can be computed for materials that form solid solutions.
- arXiv:2003.09757 [pdf, other]
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Title: Solidification Characteristics of Laser-Powder Bed Fused AlSi10Mg: Role of Building DirectionAuthors: Hossein Azizi, Alireza Ebrahimi, Nana Ofori-Opoku, Michael Greenwood, Nikolas Provatas, Mohsen MohammadiComments: 14 pages, 10 figures, two tablesSubjects: Materials Science (cond-mat.mtrl-sci); Applied Physics (physics.app-ph); Computational Physics (physics.comp-ph)
In this work, the effect of building direction on the microstructure evolution of laser-powder bed fusion (LPBF) processed AlSi10Mg alloy was investigated. The building direction, as shown in experimentally fabricated parts, can influence the solidification behavior and promote morphological transitions in cellular dendritic microstructures. We develop a thermal model to systemically address the impact of laser processing conditions, and building direction on the thermal characteristics of the molten pool during laser processing of AlSi10Mg alloy. We then employ a multi-order parameter phase field model to study the microstructure evolution of LPBF-AlSi10Mg in the dilute limit, using the underlying thermal conditions for horizontal and vertical building directions as input. The phase field model employed here is designed to simulate solidification using heterogeneous nucleation from inoculant particles allowing to take into account morphological phenomena including the columnar-to-equiaxed transition (CET). The phase field model is first validated against the predictions of the previously developed steady-state CET theory of Hunt \cite{hunt1984steady}. It is then used under transient conditions to study microstructure evolution, revealing that the nucleation rate is noticeably higher in the horizontally built samples due to larger constitutional undercooling, which is consistent with experimental observations. We further quantify the effect of building direction on the local cooling conditions, and consequently on the grain morphology.
- arXiv:2003.09765 [pdf, other]
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Title: Simulating disordered quantum systems via dense and sparse restricted Boltzmann machinesComments: 11 pages, 5 figuresSubjects: Computational Physics (physics.comp-ph); Disordered Systems and Neural Networks (cond-mat.dis-nn); Other Condensed Matter (cond-mat.other)
In recent years, generative artificial neural networks based on restricted Boltzmann machines (RBMs) have been successfully employed as accurate and flexible variational wave functions for clean quantum many-body systems. In this article we explore their use in simulations of disordered quantum spin models. The standard dense RBM with all-to-all inter-layer connectivity is not particularly appropriate for large disordered systems, since in such systems one cannot exploit translational invariance to reduce the amount of parameters to be optimized. To circumvent this problem, we implement sparse RBMs, whereby the visible spins are connected only to a subset of local hidden neurons, thus reducing the amount of parameters. We assess the performance of sparse RBMs as a function of the range of the allowed connections, and compare it with the one of dense RBMs. Benchmark results are provided for two sign-problem free Hamiltonians, namely pure and random quantum Ising chains. The RBM ansatzes are trained using the unsupervised learning scheme based on projective quantum Monte Carlo (PQMC) algorithms. We find that the sparse connectivity facilitates the training process and allows sparse RBMs to outperform the dense counterparts. Furthermore, the use of sparse RBMs as guiding functions for PQMC simulations allows us to perform PQMC simulations at a reduced computational cost, avoiding possible biases due to finite random-walker populations. We obtain unbiased predictions for the ground-state energies and the magnetization profiles with fixed boundary conditions, at the ferromagnetic quantum critical point. The magnetization profiles agree with the Fisher-de Gennes scaling relation for conformally invariant systems, including the scaling dimension predicted by the renormalization-group analysis.
- arXiv:2003.09766 [pdf, other]
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Title: Subsystem Rényi Entropy of Thermal Ensembles for SYK-like modelsComments: 20 pages, 4 figuresSubjects: Strongly Correlated Electrons (cond-mat.str-el); Quantum Physics (quant-ph)
The Sachdev-Ye-Kitaev model is an $N$-modes fermionic model with infinite range random interactions. In this work, we study the thermal R\'enyi entropy for a subsystem of the SYK model using the path-integral formalism in the large-$N$ limit. The results are consistent with exact diagonalization [1] and can be well approximated by thermal entropy with an effective temperature [2] when subsystem size $M\leq N/2$. We also consider generalizations of the SYK model with quadratic random hopping term or $U(1)$ charge conservation.
- arXiv:2003.09782 [pdf, ps, other]
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Title: Multiple Superconducting Phases and Unusual Enhancement of the Upper Critical Field in UTe2Authors: Dai Aoki, Fuminori Honda, Georg Knebel, Daniel Braithwaite, Ai Nakamura, DeXin Li, Yoshiya Homma, Yusei Shimizu, Yoshiki J. Sato, Jean-Pascal Brison, Jacques FlouquetComments: 6 pages, 5 figures, accepted for publication in J. Phys. Soc. JpnJournal-ref: J. Phys. Soc. Jpn. 89, 053705 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el); Superconductivity (cond-mat.supr-con)
We performed AC calorimetry and magnetoresistance measurements under pressure for H || a-axis (easy-magnetization axis) in the novel heavy-fermion superconductor UTe2. Thanks to the thermodynamic information, multiple superconducting phases have been revealed under pressure and magnetic field. The (H,T) phase diagram of superconductivity under pressure displays an abrupt increase of the upper critical field (Hc2) at low temperature and in the high field region, and a strong convex curvature of Hc2 at high temperature. This behavior of Hc2 and the multiple superconducting phases require a state for the superconducting order parameter more complex than a spin-triplet equal spin pairing. Above the superconducting critical pressure, Pc, we find strong indications that the possible magnetic order is closer to antiferromagnetism than to ferromagnetism.
- arXiv:2003.09803 [pdf, other]
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Title: Jaynes-Cummings model under monochromatic drivingComments: 8 pages, 13 figuresSubjects: Quantum Physics (quant-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Optics (physics.optics)
We study analytically and numerically the properties of Jaynes-Cummings model under monochromatic driving. The analytical results allow to understand the regime of two branches of multi-photon excitation in the case of close resonance between resonator and driven frequencies. The rotating wave approximation allows to reduce the description of original driven model to an effective Jaynes-Cummings model with strong coupling between photons and qubit. The analytical results are in a good agreement with the numerical ones even if there are certain deviations between the theory and numerics in the close vicinity of the resonance. We argue that the rich properties of driven Jaynes-Cummings model represent a new area for experimental investigations with superconducting qubits and other systems.
- arXiv:2003.09804 [pdf, ps, other]
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Title: Origin of superconductivity and giant phonon softening in TlInTe$_2$ under pressureAuthors: Sorb Yesudhas, N. Yedukondalu, Manoj K. Jana, Jianbo Zhang, Jie Huang, Bijuan Chen, Hongshang Deng, Raimundas Sereika, Hong Xiao, Stanislav Sinogeikin, Curtis Kenney-Benson, Kanishka Biswas, John B. Parise, Yang Ding, Ho-kwang MaoComments: 43 pages (27 pages for main text and 16 pages for SI), 20 figures (5 in main text and 15 in SI)Subjects: Superconductivity (cond-mat.supr-con)
Analogous to 2D layered transition metal dichalcogenides, the TlSe family of 1D chain materials with Zintl-type structure exhibits exotic phenomena under high-pressure. In the present work, we have systematically investigated the high-pressure behavior of TlInTe 2 using Raman spectroscopy, synchrotron X-ray diffraction, and transport measurements, in combination with crystal structure prediction (CSP) based on the evolutionary approach and first principles calculations. We found that TlInTe$_2$ undergoes a pressure driven semiconductor to semimetal transition at 4 GPa, followed by a superconducting transition at 5.7 GPa (with Tc = 3.8 K) induced by a Lifshitz transition. The Lifshitz transition is initiated by the appearance of new electron pockets on the Fermi surface, which evolve with pressure and connect to the adjacent electron pockets forming an umbrella shaped Fermi surface at the top and bottom of the Brillouin zone. An unusual giant phonon softening (Ag mode) concomitant with a V-shaped Tc behavior appears at 10-12 GPa as a result of the interaction of optical phonons with the conduction electrons, resulting in Fano line shaped asymmetry in Ag mode. A prominent Tc anomaly concurrent with the Ag mode softening at 19-20 GPa is correlated to the semimetal to metal transition. The CSP calculations reveal that these transitions are not accompanied by any structural phase transitions up to the maximum pressure achieved, 33.5 GPa. Our findings on TlInTe$_2$ open up a new platform to study a plethora of unexplored high pressure novel phenomena in TlSe family induced by Lifshitz transition (electronic driven), phonon softening and electron-phonon coupling.
- arXiv:2003.09807 [pdf]
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Title: Gate-Tunable Semiconductor Heterojunctions from 2D/3D van der Waals InterfacesAuthors: Jinshui Miao, Xiwen Liu, Kiyoung Jo, Kang He, Ravindra Saxena, Baokun Song, Huiqin Zhang, Jiale He, Myung-Geun Han, Weida Hu, Deep JariwalaComments: Manuscript plus supporting information, 4 FiguresJournal-ref: Nano Letters 2020Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci); Applied Physics (physics.app-ph)
Van der Waals (vdW) semiconductors are attractive for highly scaled devices and heterogeneous integration since they can be isolated into self-passivated, two-dimensional (2D) layers that enable superior electrostatic control. These attributes have led to numerous demonstrations of field-effect devices ranging from transistors to triodes. By exploiting the controlled, substitutional doping schemes in covalently-bonded, three-dimensional (3D) semiconductors and the passivated surfaces of 2D semiconductors, one can construct devices that can exceed performance metrics of 'all-2D' vdW heterojunctions. Here, we demonstrate, 2D/3D semiconductor heterojunctions using MoS2 as the prototypical 2D semiconductor laid upon Si and GaN as the 3D semiconductor layers. By tuning the Fermi levels in MoS2, we demonstrate devices that concurrently exhibit over seven orders of magnitude modulation in rectification ratios and conductance. Our results further suggest that the interface quality does not necessarily affect Fermi-level tuning at the junction opening up possibilities for novel 2D/3D heterojunction device architectures.
- arXiv:2003.09823 [pdf, other]
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Title: On the singular nature of the elastocapillary ridgeAuthors: A. Pandey, B. Andreotti, S. Karpitschka, G. J. van Zwieten, E. H. van Brummelen, J. H. SnoeijerComments: 17 Pages, 7 figuresSubjects: Soft Condensed Matter (cond-mat.soft)
The functionality of soft interfaces is crucial to many applications in biology and surface science. Recent studies have used liquid drops to probe the surface mechanics of elastomeric networks. Experiments suggest an intricate surface elasticity, also known as the Shuttleworth effect, where surface tension is not constant but depends on substrate deformation. However, interpretations have remained controversial due to singular elastic deformations, induced exactly at the point where the droplet pulls the network. Here we reveal the nature of the elastocapillary singularity on a hyperelastic substrate with various constitutive relations for the interfacial energy. First, we finely resolve the vicinity of the singularity using goal-adaptive finite element simulations. This confirms the universal validity, also at large elastic deformations, of the previously disputed Neumann's law for the contact angles. Subsequently, we derive exact solutions of nonlinear elasticity that describe the singularity analytically. These solutions are in perfect agreement with numerics, and show that the stretch at the contact line, as previously measured experimentally, consistently points to a strong Shuttleworth effect. Finally, using Noether's theorem we provide a quantitative link between wetting hysteresis and Eshelby-like forces, and thereby offer a complete framework for soft wetting in the presence of the Shuttleworth effect.
- arXiv:2003.09824 [pdf, other]
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Title: Self-assembly of Freely-rotating Polydisperse Cuboids: Unveiling the Boundaries of the Biaxial Nematic PhaseSubjects: Soft Condensed Matter (cond-mat.soft)
Colloidal cuboids have the potential to self-assemble into biaxial liquid crystal phases, which exhibit two independent optical axes. Over the last few decades, several theoretical works predicted the existence of a wide region of the phase diagram where the biaxial nematic phase would be stable, but imposed rather strong constraints on the particle rotational degrees of freedom. In this work, we employ molecular simulation to investigate the impact of size dispersity on the phase behaviour of freely-rotating hard cuboids, here modelled as self-dual-shaped nanoboards. This peculiar anisotropy, exactly in between oblate and prolate geometry, has been proposed as the most appropriate to promote phase biaxiality. We observe that size dispersity radically changes the phase behaviour of monodisperse systems and leads to the formation of the elusive biaxial nematic phase, being found in an large region of the packing fraction vs polydispersity phase diagram. Although our results confirm the tendencies reported in past experimental observations on colloidal dispersions of slightly prolate goethite particles, they cannot reproduce the direct isotropic-to-biaxial nematic phase transition observed in these experiments.
- arXiv:2003.09835 [pdf]
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Title: Fulleryne, a new member of the carbon cages familyComments: 18 pages, 9 figuresSubjects: Materials Science (cond-mat.mtrl-sci); Computational Physics (physics.comp-ph)
In this study, based on density functional theory (DFT), we propose a new branch of pseudo-fullerenes which contain triple bonds with sp hybridization. We should call these new nanostructures fullerynes, according to IUPAC. We present four samples with the chemical formula of C4nHn, and structures derived from fullerenes. We compare the structural and electronic properties of these structures with those of two common fullerene and fullerene systems. The calculated electron affinities of the sampled fullerynes are negative, and much smaller than those of fullerenes, so they should be chemically more stable than fullerenes. Although fulleranes also exhibit higher chemical stability than fullerynes, but pentagon or hexagon of the fullerane structures cannot pass ions and molecules. Applications of fullerynes can be included in the storage of ions and gases at the nanoscale. On the other hand, they can also be used as cathode/anode electrodes in lithium-ion batteries.
- arXiv:2003.09836 [pdf]
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Title: The emergence of magnetic skyrmionsComments: 5 Pages, 4 Figures, 1 BoxJournal-ref: Physics Today 73(3), 44 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
This is a narrative of the basic theoretical ideas of axisymmetric two-dimensional solitons and of their connection to basic experiments on magnetic compounds. A shortened and edited version appeared in Physics Today.
- arXiv:2003.09840 [pdf]
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Title: Thermoelectric probe of defect state induced by ionic liquid gating in vanadium dioxideJournal-ref: Appl. Phys. Lett. 116, 193502 (2020)Subjects: Materials Science (cond-mat.mtrl-sci)
Thermoelectric measurements detect the asymmetry between the density of states above and below the chemical potential in a material. It provides insights into small variations in the density of states near the chemical potential, complementing electron transport measurements. Here, combined resistance and thermoelectric power measurements are performed on vanadium dioxide (VO2), a prototypical correlated electron material, under ionic-liquid (IL) gating. With IL gating, charge transport below the metal-to-insulator-transition (MIT) temperature remains in the thermally activated regime, while the Seebeck coefficient exhibits an apparent transition from semiconducting to metallic behavior. The contrasting behavior indicates changes in electronic structure upon IL gating, due to the formation of oxygen defect states. The experimental results are corroborated by numerical simulations based on a model density of states incorporating a gating induced defect band. This study reveals thermoelectric measurements to be a convenient and sensitive probe for the role of defect states induced by IL gating in suppressing the MIT in VO2, which remains benign in charge transport measurements, and possibly for studying defect sates in other materials.
- arXiv:2003.09858 [pdf, other]
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Title: Carbamazepine solubility in supercritical CO$_2$: a comprehensive studyAuthors: N.N. Kalikin, M.V. Kurskaya, D.V. Ivlev, M.A. Krestyaninov, R.D. Oparin, A.L. Kolesnikov, Y.A. Budkov, A. Idrissi, M.G. KiselevComments: 17 pages, 6 figures, 3 tablesSubjects: Materials Science (cond-mat.mtrl-sci); Chemical Physics (physics.chem-ph)
In this paper we present our study of carbamazepine solubility in supercritical carbon dioxide. We have calculated the solubility values along two isochores corresponding to the CO$_2$ densities $\rho = 1.1\rho_{cr}(CO_2)$ and $\rho= 1.3\rho_{cr}(CO_2)$, where $\rho_{cr}(CO_2)$ is the critical density of CO$_2$, in the temperature range from $313$ to $383~K$, as well as along three isotherms at $T=318$, $328$ and $348~K$ by an approach based on the classical density functional theory. The solubility values were also obtained using in situ IR spectroscopy and molecular dynamics simulations along the mentioned isochores and isotherms, respectively. Because the density functional theory only takes into account the Lennard-Jones interactions, it can be expected to underestimate the solubility values when compared to the experimental ones. However, we have shown that the data calculated within the classical density functional theory qualitatively reproduce the solubility trends obtained by IR spectroscopy and molecular dynamics simulation. Moreover, the obtained position of the upper crossover pressure is in good agreement with the experimental literature results.
- arXiv:2003.09859 [pdf]
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Title: Mott Transition and Superconductivity in Quantum Spin Liquid Candidate NaYbSe$_2$Authors: Yating Jia, Chunsheng Gong, Yixuan Liu, Jianfa Zhao, Cheng Dong, Guangyang Dai, Xiaodong Li, Hechang Lei, Runze Yu, Guangming Zhang, Changqing JinComments: 20 pages, 6 figuresSubjects: Superconductivity (cond-mat.supr-con); Strongly Correlated Electrons (cond-mat.str-el)
The Mott transition is one of the fundamental issues in condensed matter physics, especially in the system with antiferromagnetic long-range order. However the Mott transition in quantum spin liquid (QSL) systems without long-range order is rare. Here we report the observation of the pressure-induced insulator to metal transition followed by the emergence of superconductivity in the QSL candidate NaYbSe2 with triangular lattice of 4f Yb$_3^+$ ions. Detail analysis of transport properties at metallic state shows an evolution from non-Fermi liquid to Fermi liquid behavior when approaching the vicinity of superconductivity. An irreversible structure phase transition occurs around 11 GPa is revealed by the X-ray diffraction and Raman spectrum. These results shed light on the Mott transition and superconductivity in the QSL systems.
- arXiv:2003.09864 [pdf, ps, other]
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Title: Theoretical Study of Ternary CoSP Semiconductor: a Candidate for Photovoltaic ApplicationsComments: 3 figuresJournal-ref: Advanced Theory and Simulations, 2019Subjects: Materials Science (cond-mat.mtrl-sci)
The electronic structure of pyrite-type cobalt phosphosulfide (CoSP) has been studied using density-functional theory. The calculated band structure reveals the non-magnetic semiconducting character of the compound. The electronic structure is described through the electronic band structure and the densities of states. A band gap of 1.14 eV has been computed within standard GGA, a value which is enhanced using hybrid functional. It separates the upper part of the valence band dominated by Co-3d-t2g states from the lower part of the conduction band made exclusively of Co-3d-eg , above of which lie S-3p and P-3p ones. The obtained values are suitable for applications in solar cells, according to Shockley-Queisser theory of light to electric conversion efficiency. The origin of the larger CoSP band gap, with respect to the one of the promising FeS2 compound, is explained and the chemical bonding properties are addressed. A comparative picture is established where several similarities have been found, suggesting that CoSP could be for a great practical interest in photovoltaics.
- arXiv:2003.09866 [pdf, ps, other]
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Title: Kinetic energy of the Langevin particleAuthors: Carlos EscuderoSubjects: Probability (math.PR); Statistical Mechanics (cond-mat.stat-mech); Mathematical Physics (math-ph)
We compute the kinetic energy of the Langevin particle using different approaches. We build stochastic differential equations that describe this physical quantity based on both the It\^o and Stratonovich stochastic integrals. It is shown that the It\^o equation possesses a unique solution whereas the Stratonovich one possesses infinitely many, all but one absent of physical meaning. We discuss how this fact matches with the existent discussion on the It\^o vs Stratonovich dilemma and the apparent preference towards the Stratonovich interpretation in the physical literature.
- arXiv:2003.09872 [pdf]
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Title: Effects of magic angle on crystal and electronic structures of bilayer transition metal dichalcogenidesSubjects: Materials Science (cond-mat.mtrl-sci); Applied Physics (physics.app-ph)
In this work, we employ the LDA, GGA and GGA with four vdW corrections to study crystal and electronic structures of bilayer transition metal dichalcogenides (TMDs) with different magic angles (Moir\'e superlattice). Our results indicate the GGA interlayer distances of bilayer TMDs with magic angles are smaller than that of normal bilayer, which is the opposite of the LDA case. Comparing the experimental and theoretical data, we consider that the pure GGA is suitable for study of Moir\'e superlattice while vdW correction methods still needs to be further optimized. The GGA results show that magic angle can shorten the interlayer distance and thus narrow the bandgap and widths of valley band and conductivity band. Our study not only supports valuable information for application possibility of TMD Moir\'e superlattice but also stimulates more related research.
- arXiv:2003.09882 [pdf]
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Title: High-temperature oxygen monolayer structures on W(110) revisitedAuthors: Dorota Wilgocka-Ślęzak (1), Tomasz Giela (2), Kinga Freindl (1), Nika Spiridis, (1) Józef Korecki (1 and 3) ((1) Jerzy Haber Institute of Catalysis and Surface Chemistry, Polish Academy of Sciences, Cracow, Poland (2) National Synchrotron Radiation Centre SOLARIS, Jagiellonian University, Cracow, Poland (3) AGH University of Science and Technology, Faculty of Physics and Applied Computer Science, Cracow, Poland)Subjects: Materials Science (cond-mat.mtrl-sci)
Systematic studies of the two high-temperature monolayer oxygen structures that exist on the (110) tungsten surface were performed using low-energy electron microscopy and diffraction measurements. Our work questions the commonly accepted interpretation from the literature that striped oxygen superstructures arise from alternating site-exchanged (S-E) domains. We postulate that the superstructures originate from a misfit between tungsten and oxygen lattices while the striped appearance corresponds to a moir\'e pattern. Moreover, we show that the two structures, indicated as 113- and 337-phases due to the characteristic directions of the respective moir\'e patterns, differ considerably in their symmetry properties. This suggests that oxygen atoms in the two overlayers occupy different adsorption sites on average. In particular, the 113-phase features rotational domains that retain mirror symmetries with respect to the [001] and [1-10] directions, whereas the 337-phase is characterized by the appearance of additional domains due to the breaking of these symmetries. We propose structural models for both phases that consistently explain their unusual properties and suggest a universal mechanism for the thermal evolution of oxygen monolayer adsorbed on W(110).
- arXiv:2003.09885 [pdf, other]
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Title: Dynamics of Rydberg excitations and quantum correlations in an atomic array coupled to a photonic crystal waveguideComments: 15 pages, 16 figuresSubjects: Quantum Gases (cond-mat.quant-gas); Quantum Physics (quant-ph)
We study the dynamics of up to two Rydberg excitations and the correlation growth in a chain of atoms coupled to a photonic crystal waveguide. In this setup, an excitation can hop from one atom to another via exponentially decaying exchange interactions mediated by the waveguide. An initially localized excitation undergoes a continuous-time quantum walk for short-range hopping, and for long-range, it experiences quasi-localization. Besides that, the inverse participation ratio reveals a super-ballistic diffusion of the excitation in short times, whereas, at a long time, it becomes ballistic. For two initially localized excitations, intriguing, and complex dynamical scenarios emerge for different initial separations due to the competition between the Rydberg-Rydberg and exchange interactions. In particular, the two-point correlation reveals a light-cone behavior even for sufficiently long-range exchange interactions. Additionally, we characterize the growth of bipartite entanglement entropy, which exhibits a global bound if only one excitation is present in the dynamics. Finally, we analyze the effect of imperfections due to spontaneous emission from the Rydberg state into photons outside the waveguide and show that all physical phenomena we predict are well within experimental reach.
- arXiv:2003.09903 [pdf, other]
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Title: Quantum boomerang effect for interacting particlesComments: 7 + 2 pages, 9 + 2 figures, added discussion about strong disorder case in ConclusionSubjects: Disordered Systems and Neural Networks (cond-mat.dis-nn)
When a quantum particle is launched with a finite velocity in a disordered potential, it may surprisingly come back to its initial position at long times and remain there forever. This phenomenon, dubbed ``quantum boomerang effect'', was introduced in [Phys. Rev. A 99, 023629 (2019)]. Interactions between particles, treated within the mean-field approximation, are shown to partially destroy the boomerang effect: the center of mass of the wave packet makes a U-turn, but does not completely come back to its initial position. We show that this phenomenon can be quantitatively interpreted using a single parameter, the average interaction energy.
- arXiv:2003.09905 [pdf, other]
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Title: Unsupervised phase discovery with deep anomaly detectionComments: 5 + 4 pages, 7 + 7 figures, readable code at this https URL, comments welcomeSubjects: Quantum Physics (quant-ph); Disordered Systems and Neural Networks (cond-mat.dis-nn)
We demonstrate how to discover unknown quantum phases in many body systems using automated and unsupervised machine learning. In contrast to supervised learning, where data is classified using predetermined labels, we here perform anomaly detection, where the task is to differentiate a normal data set, composed of one or several classes, from anomalous data. As a paradigmatic example, we explore the phase diagram of the extended Bose Hubbard model in one dimension at exact integer filling and employ deep neural networks to determine the entire phase diagram in a completely unsupervised and automated fashion. As input data for learning, we first use the entanglement spectra and central tensors derived from tensor-networks algorithms for ground-state computation and later we extend our method and use experimentally accessible data such as low-order correlation functions as inputs. Our method allow us to reveal a supersolid state with unexpected properties, which appears in the system in addition to the standard superfluid, Mott insulator, Haldane-insulating, and density wave phases.
- arXiv:2003.09912 [pdf, ps, other]
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Title: Comment on "Amplitude of waves in the Kelvin-wave cascade"Authors: E.B. SoninComments: 2 pagesSubjects: Other Condensed Matter (cond-mat.other)
In the recently published preprint arXiv:200.02610 Eltsov and L'vov calculated the amplitudes of waves in the Kelvin-wave cascades. This returns us to the rather old, but still unresolved dispute on the role of the tilt symmetry and the locality in the Kelvin-wave cascade. The estimations by Eltsov and L'vov show that the possible nonlocality of the energy flux in the Kelvin-wave cascade has no essential effect on the Kelvin-wave cascade in the 3D vortex tangle.
- arXiv:2003.09932 [pdf, other]
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Title: Constitutive relations for plasticity of amorphous carbonAuthors: Richard Jana, Julian von Lautz, S. Mostafa Khosrownejad, W. Beck Andrews, Michael Moseler, Lars PastewkaComments: 12 pages, 3 figuresSubjects: Materials Science (cond-mat.mtrl-sci)
We deform representative volume elements of amorphous carbon obtained from melt-quenches in molecular dynamics calculations using bond-order and machine learning interatomic potentials. A Drucker-Prager law with a zero-pressure flow stress of $41.2$~GPa and an internal friction coefficient of $0.39$ describes the deviatoric stress during flow as a function of pressure. We identify the mean coordination number as the order parameter describing this flow surface. However, a description of the dynamical relaxation of the quenched samples towards steady-state flow requires an additional order parameter. We suggest an intrinsic strain of the samples as a possible order parameter and present equations for its evolution. Our results provide insights into rehybridization and pressure dependence of friction between coated surfaces as well as routes towards the description of amorphous carbon in macroscale models of deformation.
- arXiv:2003.09936 [pdf, ps, other]
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Title: Engineering Corner States from Two-Dimensional Topological InsulatorsJournal-ref: Phys. Rev. Lett. 124, 166804 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We theoretically demonstrate that the second-order topological insulator with robust corner states can be realized in two-dimensional $\mathbb{Z}_2$ topological insulators by applying an in-plane Zeeman field. Zeeman field breaks the time-reversal symmetry and thus destroys the $\mathbb{Z}_2$ topological phase. Nevertheless, it respects some crystalline symmetries and thus can protect the higher-order topological phase. By taking the Kane-Mele model as a concrete example, we find that spin-helical edge states along zigzag boundaries are gapped out by Zeeman field whereas in-gap corner state at the intersection between two zigzag edges arises, which is independent on the field orientation. We further show that the corner states are robust against the out-of-plane Zeeman field, staggered sublattice potentials, Rashba spin-orbit coupling, and the buckling of honeycomb lattices, making them experimentally feasible. Similar behaviors can also be found in the well-known Bernevig-Hughes-Zhang model.
- arXiv:2003.09942 [pdf, other]
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Title: A simple electron-counting rule to determine the interlayer magnetic coupling of the van der Waals materialsSubjects: Materials Science (cond-mat.mtrl-sci)
In layered magnetic materials, the magnetic coupling between neighboring van der Waals layers is challenging to understand and anticipate, although the exchange interaction inside a layer can be well rationalized for example by the superexchange mechanism. In this work, we propose a simple electron-counting rule to determine the interlayer magnetic order between van der Waals layers. This method is based on counting the $d$-orbital occupation ($d^n$, where $n$ is the number of $d$-electrons at the magnetic cation), as a generalization of the Goodenough-Kanamori superexchange rules to the interlayer exchange coupling. With this rule, we classify magnetic monolayers into two groups, type-I ($n<5$) and type-II ($n\geq5$), and derive three types of interlayer magnetic coupling for both insulators and metals. The coupling between two type-II layers prefers the antiferromagnetic (AFM) way, that between the type-I and type-II favors the ferromagnetic (FM) way, while that between two type-I layers displays a competition among the FM and AFM orders. Additionally, the exchange coupling between metallic layers requires a minor correction by the itinerant carriers. This rule provides a simple guidance to design van der Waals junctions with the desired magnetic order.
- arXiv:2003.09949 [pdf, other]
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Title: Non-backtracking walks reveal compartments in sparse chromatin interaction networksSubjects: Molecular Networks (q-bio.MN); Statistical Mechanics (cond-mat.stat-mech)
Chromatin communities stabilized by protein machinery play essential role in gene regulation and refine global polymeric folding of the chromatin fiber. However, treatment of these communities in the framework of the classical stochastic block model (SBM) does not take into account linear connectivity of the chromatin. Here we propose the "polymer" variant of the SBM, paving the way for spectral community detection in polymer networks. Statistical inference of the model generalizes the Newman's modularity to the case of stochastic networks with hidden linear memory. In single cell chromatin interaction networks the optimal partition can be inferred from localization of the non-backtracking walks on the corresponding polymer graph, which responds to the maximum entropy principle. The benchmark analyses demonstrates that the spectrum of the polymer non-backtracking allows to resolve the true compartmental structure up to the detectability threshold, while traditionally used operators fail above it. Finally, we show that the polymer non-backtracking walks reveal the compartmental structure in single cell Hi-C maps. The found clusters have similar sizes with the domains from the population data and differ in the gene density, corroborating biological significance of the partition into active and inactive compartments.
- arXiv:2003.09954 [pdf]
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Title: Light-driven permanent transition from insulator to conductor in Ga2O3Authors: F. A. Selim, D. Rana, S. Agarwal, M. Islam, A. Banerjee, B. P. Uberuaga, P. Saadatkia, P. Dulal, N. Adhikari, M. Butterling, M. O. Liedke, A. WagnerComments: 24 pages, 10 figuresSubjects: Materials Science (cond-mat.mtrl-sci)
The transition from insulator to conductor can be achieved in some materials but requires modification of both the arrangement of atoms and their electronic configurations. This is often achieved by doping. Here we reveal a mechanism the lattice may adopt to induce such a transition. We show that limited exposure to sub-bandgap light caused a permanent transition from an insulator state to a conductor state in the insulating oxide Ga2O3 with 9-orders of magnitude increase in electronic conduction. Photoexcitation modifies the charge state of an O-vacancy and the redistribution of the localized electrons, leading to a massive structural distortion in the lattice that is shown to be the underlying mechanism. It modifies density of states and introduces new stable states with shallower energy levels, leading to this intriguing behavior. We suggest that this mechanism may occur in other wide bandgap metal oxides leading to drastic modification in their electronic properties.
- arXiv:2003.09966 [pdf, ps, other]
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Title: Quantum paraelectric state and critical behavior in Sn(Pb)$_2$P$_2$S(Se)$_6$ ferroelectricsAuthors: I. Zamaraite, V. Liubachko, R. Yevych, A. Oleaga, A. Salazar, A. Dziaugys, J. Banys, Yu. VysochanskiiSubjects: Materials Science (cond-mat.mtrl-sci)
The dipole ordering in Sn(Pb)$_2$P$_2$S(Se)$_6$ materials may be tuned by chemical substitution realizing a ferroelectric quantum phase transition and quantum glassy or relaxor type phenomena on different parts of the phase diagram. The introduction of Ge impurity increases the temperature of the phase transitions and initiates a more pronounced Ising type critical anomaly in Sn$_2$P$_2$S$_6$ crystal, does not shift the coordinate of the Lifshitz point $x_{\textrm {LP}}$ in Sn$_2$P$_2$(Se$_x$S$_{1-x}$)$_6$ mixed crystals, induces the appearance of a ferroelectric phase transition in quantum paraelectrics Pb$_2$P$_2$S$_6$ and inhomogeneous polar ordering in (Pb$_{0.7}$Sn$_{0.3}$)$_2$P$_2$S(Se)$_6$ crystals. For Pb$_2$P$_2$S$_6$ crystal, the real part of the dielectric susceptibility in the quantum critical regime varies as $1/T^2$ instead of the expected $1/T^3$ behavior for uniaxial materials. This can be partially explained by a screening phenomenon in the semiconductor materials of the Sn(Pb)$_2$P$_2$S(Se)$_6$ system, which weakens the long range electric dipole interactions, and also provides, at high temperatures, a critical behavior near the Lifshitz point (studied by thermal diffusivity) similar to the one predicted in the case of systems with short range interactions. At low temperatures, a quantum critical behavior in Pb$_2$P$_2$S$_6$ crystal can be established by the nonlinear coupling between polar and antipolar fluctuations. An increase in thermal conductivity is induced by Ge impurity in Pb$_2$P$_2$S$_6$ crystal, which is explained through the weakening of the acoustic phonons resonance scattering by soft optic phonons because of the appearance of ferroelectric phase polar clusters.
- arXiv:2003.09973 [pdf]
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Title: Numerical Investigation of Mechanical Properties of Aluminum Alloys at NanoscaleAuthors: Satyajit Mojumder, Md Shajedul Hoque Thakur, Mahmudul Islam, Monon Mahboob, Mohammad MotalabComments: Manuscript: 33 pages, 14 figures; Supplementary: 10 pages, 7 figuresSubjects: Materials Science (cond-mat.mtrl-sci)
Nanoindentation is a powerful tool capable of providing fundamental insights of material elastic and plastic response at the nanoscale.Alloys at nanoscale are particularly interesting as the local heterogeneity and deformation mechanism revealed by atomistic study offers a better way to understand hardening mechanism to build a stronger material. In this work, nanoindentation in Al-Mg alloys are studied using atomistic simulations to investigate the effects of loading direction, alloying percentages of Mg via dislocation-driven mechanisms. Also, finite element (FE) nanoindentation simulations are performed using MD tensile test results as input parameters for the FE simulations. Material properties, such as hardness and reduced modulus, are computed from both the FE and MD simulations and then compared. Considering the fundamental difference between these two numerical approaches, the FE results obtained from the present study conform fairly with those from MD simulations. This paves a way into finding material properties of alloys with reduced simulation time and cost by using FE instead of MD. The results have been presented as load-displacement analysis, dislocation density, dislocation loops nucleation and propagation, von-Mises stress distribution and surface imprints. The techniques adopted in this paper to incorporate atomistic data into FE simulations can be further extended for finding other mechanical and fracture properties for complex alloy materials.
- arXiv:2003.09990 [pdf, other]
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Title: Variations on a Demonic Theme: Szilard's Other EnginesComments: 15 pages, 14 figures; Supplementary Materials, pages; this http URLSubjects: Statistical Mechanics (cond-mat.stat-mech); Information Theory (cs.IT); Chaotic Dynamics (nlin.CD)
Szilard's now-famous single-molecule engine was only the first of three constructions he introduced in 1929 to resolve several paradoxes arising from Maxwell's demon. We analyze Szilard's remaining two demon models. We show that the second one, though a markedly different implementation employing a population of distinct molecular species and semi-permeable membranes, is informationally and thermodynamically equivalent to an ideal gas of the single-molecule engines. Since it is a gas of noninteracting particles one concludes, following Boyd and Crutchfield, that (i) it reduces to a chaotic dynamical system---called the Szilard Map, a composite of three piecewise linear maps that implement the thermodynamic transformations of measurement, control, and erasure; (ii) its transitory functioning as an engine that converts disorganized heat energy to work is governed by the Kolmogorov-Sinai entropy rate; (iii) the demon's minimum necessary "intelligence" for optimal functioning is given by the engine's statistical complexity, and (iv) its functioning saturates thermodynamic bounds and so it is a minimal, optimal implementation. We show that Szilard's third model is rather different and addresses the fundamental issue, raised by the first two, of measurement in and by thermodynamic systems and entropy generation. Taken together, Szilard's suite of constructions lays out a range of possible realizations of Maxwellian demons that anticipated by almost two decades Shannon's and Wiener's concept of information as surprise and cybernetics' notion of functional information. This, in turn, gives new insight into engineering implementations of novel nanoscale information engines that leverage microscopic fluctuations and into the diversity of thermodynamic mechanisms and intrinsic computation harnessed in physical, molecular, biochemical, and biological systems.
- arXiv:2003.09997 [pdf]
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Title: Monitoring of the formation of strontium molybdate intergrain tunneling barriers in strontium ferromolybdateComments: 18 pages, 5 figuresSubjects: Materials Science (cond-mat.mtrl-sci)
This work is a contribution to the understanding of the electrical resistivity in strontium ferromolybdate (SFMO) ceramics. It demonstrates that an appropriate thermal treatment leads to the formation of dielectric SrMoO4 shells at the surface of SFMO nanograins. In samples without SrMoO4 shells, the sign of the temperature coefficient of resistance changes with increasing temperature from negative at very low temperature to positive at higher temperatures. Samples exhibiting a negative temperature coefficient contain SrMoO4 shells and demonstrate a behavior of the resistivity that can be described in terms of the fluctuation-induced tunneling model, and near room temperature the conductivity mechanism converts to a variable-range hopping one. The results of this work serve as a starting point for the understanding of the low-field magnetoresistance which is very promising for spintronic device application.
- arXiv:2003.10003 [pdf, other]
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Title: Emergent dynamics in excitable flow systemsSubjects: Soft Condensed Matter (cond-mat.soft); Fluid Dynamics (physics.flu-dyn)
Flow networks can describe many natural and artificial systems. We present a model for a flow system that allows for volume accumulation, includes conduits with a non-linear relation between current and pressure difference, and can be applied to networks of arbitrary topology. The model displays complex dynamics, including self-sustained oscillations in the absence of any dynamics in the inputs and outputs. In this work we analytically show the origin of self-sustained oscillations for the 1D case. We numerically study the behavior of systems of arbitrary topology under different conditions: we discuss their excitability, the effect of different boundary conditions and wave propagation when the network has regions of conduits with linear conductance.
- arXiv:2003.10008 [pdf, other]
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Title: Topological Data Analysis of Collective and Individual Phases in a Minimal Model of Epithelial CellsSubjects: Quantitative Methods (q-bio.QM); Soft Condensed Matter (cond-mat.soft); Adaptation and Self-Organizing Systems (nlin.AO)
Interacting, self-propelled particles such as motile epithelial cells can dynamically self-organize into large-scale patterns. In such living systems, cell number and density can vary dramatically over time due to proliferation, which is not commonly considered in other active matter systems. As a consequence, it remains challenging to determine individual and collective phases over varying populations sizes without a priori information. Here, we demonstrate an unbiased machine learning approach to analyze multiparticle clusters based on topological structure, which is robust to changes in population size. For a given particle configuration, topological data analysis (TDA) determines the stability of spatial connectivity at varying length scales (i.e. persistent homology), and can compare different particle configurations based on the "cost" of reorganizing one configuration into another. We show that TDA can accurately map out phase diagrams for interacting particles with varying adhesion and self-propulsion, at constant population size as well as when proliferation is permitted. Next, we use this approach to profile our recent experiments on the clustering of epithelial cells in varying growth factor conditions. Finally, we characterize the statistical robustness of this approach over repeated simulations and with random particle removal. Overall, we envision TDA will be broadly applicable as a model-agnostic approach to analyze active systems with varying population size, from cytoskeletal motors to motile cells to flocking or swarming animals.
- arXiv:2003.10020 [pdf, other]
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Title: Programmable quantum Hall bisector: towards a novel resistance standard for quantum metrologyComments: 7 pages, 5 figures, plus SISubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Quantum Physics (quant-ph)
We demonstrate a programmable quantum Hall circuit that implements a novel iterative voltage bisection scheme and allows obtaining any binary fraction $(k/2^n)$ of the fundamental resistance quantum $R_K/2=h/2e^2$. The circuit requires a number $n$ of bisection stages that only scales logarithmically with the precision of the fraction. The value of $k$ can be set to any integer between 1 and $2^n$ by proper gate configuration. The architecture exploits gate-controlled routing, mixing and equilibration of edge modes of robust quantum Hall states. The device does not contain {\em any} internal ohmic contact potentially leading to spurious voltage drops. Our scheme addresses key critical aspects of quantum Hall arrays of resistance standards, which are today widely studied and used to create custom calibration resistances. The approach is demonstrated in a proof-of-principle two-stage bisection circuit built on a high-mobility GaAs/AlGaAs heterostructure operating at a temperature of $260\,{\rm mK}$ and a magnetic field of $4.1\,{\rm T}$.
- arXiv:2003.10049 [pdf, ps, other]
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Title: Magneto-oscillations and anomalous current states in a photo-excited electron gas on liquid heliumComments: Review paper: 40 pages, 23 figuresJournal-ref: J. Low Temp. Phys. 197, 208-249 (2019)Subjects: Strongly Correlated Electrons (cond-mat.str-el)
The paper reviews a novel class of phenomena observed recently in the two-dimensional (2D) electron system formed on the free surface of liquid helium in the presence of a magnetic field directed normally and exposed to microwave radiation. The distinctive feature of these nonequilibrium phenomena is magnetoconductivity oscillations induced by inter-subband (out-of-plane) and intra-subband (in-plane) microwave excitations. The conductivity magneto-oscillations induced by intra-subband excitation are similar to remarkable microwave-induced resistance oscillations (MIRO) reported for semiconductor heterostructures. Investigations of microwave-induced conductivity oscillations (MICO) on liquid helium helped with understanding of the origin of MIRO. Much stronger microwave-induced conductivity oscillations were observed and well described theoretically for resonant inter-subband microwave excitation. At strong powers, such excitation leads to zero-resistance states (ZRS), the in-plane redistribution of electrons, self-generated audio-frequency oscillations, and incompressible states. These phenomena are caused by unusual current states of the 2D electron system formed under resonant microwave excitation.
- arXiv:2003.10061 [pdf]
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Title: Tunable microwave absorption performance of nitrogen and sulfur dual-doped graphene by varying doping sequenceSubjects: Applied Physics (physics.app-ph); Materials Science (cond-mat.mtrl-sci)
Sulfur and nitrogen dual doped graphene have been extensively investigated in the field of oxygen reduction reaction, supercapacitors and batteries, but their magnetic and absorption performance have not been explored. Besides, the effects of doping sequence of sulfur and nitrogen atoms on the morphology, structural property and the corresponding microwave absorption performance of the dual doped graphene remain unexplored. In this work, nitrogen and sulfur dual doped graphene with different doping sequence were successfully prepared using a controllable two steps facile thermal treatment method. The first doping process played a decisive role on the morphology, crystal size, interlayer distance, doping degree and ultimately magnetic and microwave absorption properties of the dual doped graphene samples. Meanwhile, the second doping step affected the doping sites and further had a repairing or damaging effect on the final doped graphene. The dual doped graphene samples exhibited two pronounced absorption peaks which intensity was decided by the order of the doping elements. This nitrogen and sulfur dual doped graphene with controlled doping order provides a strategy for understanding of the interaction between nitrogen and sulfur as dual dopants in graphene and further acquiring microwave absorbing materials with tunable absorption bands by varying the doping sequence.
- arXiv:2003.10067 [pdf]
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Title: Supersaturation model for InN PA-MOCVDComments: 11 pages, 6 figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci)
We developed a thermodynamic supersaturation model for plasma-assisted metalorganic chemical vapor deposition of InN. The model is based on the chemical combination of indium with plasma-generated atomic nitrogen ions. Indium supersaturation was analyzed for InN films grown by PA-MOCVD with varying input flow of indium precursor. Raman spectroscopy, X-ray diffraction, and atomic force microscopy provided feedback on structural properties and surface morphology of grown films. Growth parameter variation effect on In supersaturation was analyzed. InN films grown at varying growth parameters resulting in the same In supersaturation value exhibit similar structural properties and surface morphology.
- arXiv:2003.10089 [pdf, ps, other]
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Title: Defective Edge states and Anomalous Bulk-boundary Correspondence for Topological Insulators under Non-Hermitian Similarity TransformationComments: 13pages,8figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Strongly Correlated Electrons (cond-mat.str-el)
It was known that for non-Hermitian topological systems due to the non-Hermitian skin effect, the bulk-edge correspondence is broken down. In this paper, by using one-dimensional Su-SchriefferHeeger model and two-dimensional (deformed) Qi-Wu-Zhang model as examples, we focus on a special type of non-Hermitian topological system without non-Hermitian skin effect-topological systems under non-Hermitian similarity transformation. In these non-Hermitian systems, the defective edge states and the breakdown of bulk-edge correspondence are discovered. To characterize the topological properties, we introduce a new type of inversion symmetry-protected topological invariant-total Z2 topological invariant. In topological phases, defective edge states appear. With the help of the effective edge Hamiltonian, we find that the defective edge states are protected by (generalized) chiral symmetry and thus the (singular) defective edge states are unstable against the perturbation breaking the chiral symmetry. In addition, the results are generalized to nonHermitian topological insulators with inversion symmetry in higher dimensions. This work could help people to understand the defective edge states and the breakdown of bulk-edge correspondence for non-Hermitian topological systems.
- arXiv:2003.10090 [pdf, ps, other]
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Title: Spin-orbit-coupling-assisted roton softening and superstripes in a Rydberg-dressed Bose-Einstein CondensateComments: 8 pages, 4 figuresSubjects: Quantum Gases (cond-mat.quant-gas)
Rotons can exist in ultracold atomic gases either with long-range interactions or with spin-orbitcoupled dispersions. We find that two different kinds of rotons coexist in a joint system combining long-range interactions and spin-orbit coupling. One roton originates from spin-orbit coupling and two others come from long-range interactions. Their softening can be controlled separately. The interesting new phenomenon which we find is that spin-orbit-coupled roton can push down the energy of one long-range-interaction roton. The spin-orbit coupling accelerates the softening of this roton. The post phase of spin-orbit-coupling-assisted roton softening and instability is identified as a superstripe.
- arXiv:2003.10093 [pdf, other]
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Title: Chemical characterization of dislocation in yttria-stabilized zirconiaAuthors: Kyoung-Won ParkSubjects: Materials Science (cond-mat.mtrl-sci)
This study demonstrates that a space charge layer is formed on dislocation during mechanical deformation at elevated temperature. High density of dislocation lines is generated in bulk single crystalline Y2O3 stabilized ZrO2 (YSZ) by uniaxial compression at elevated temperature. The creation of dislocation is proven with transmission electron microscopy (TEM). Then, energy-dispersive X-ray spectroscopy (EDS) and electron energy loss spectroscopy (EELS) are used to explore the changes in the composition on and away from the dislocation lines. Also, it is clarified that segregation of dopant atoms (yttrium) on the dislocation line is induced by high temperature annealing. Comparing the compositional variations with and without thermal annealing, we study the space charge layer formed on dislocation lines in a doped system.
- arXiv:2003.10096 [pdf]
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Title: Electric field thermopower modulation analyses of the operation mechanism of transparent amorphous SnO$_2$ thin-film transistorJournal-ref: Applied Physics Letters 116, 143503 (2020)Subjects: Applied Physics (physics.app-ph); Materials Science (cond-mat.mtrl-sci)
Transparent amorphous oxide semiconductors (TAOSs) based transparent thin-film transistors (TTFTs) with high field effect mobility are essential for developing advanced flat panel displays. Among TAOSs, amorphous (a-) SnO$_2$ has several advantages against current a-InGaZnO4 such as higher field effect mobility and being indium free. Although a-SnO$_2$ TTFT has been demonstrated several times, the operation mechanism has not been clarified thus far due to the strong gas sensing characteristics of SnO$_2$. Here we clarify the operation mechanism of a-SnO$_2$ TTFT by electric field thermopower modulation analyses. We prepared a bottom-gate top-contact type TTFT using 4.2-nm-thick a-SnO$_2$ as the channel without any surface passivation. The effective thickness of the conducting channel was ~1.7 + - 0.4 nm in air and in vacuum, but a large threshold gate voltage shift occurred in different atmospheres; this is attributed to carrier depletion near at the top surface (~2.5 nm) of the a-SnO$_2$ due to its interaction with the gas molecules and the resulting shift in the Fermi energy. The present results would provide a fundamental design concept to develop a-SnO$_2$ TTFT.
- arXiv:2003.10099 [pdf, ps, other]
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Title: Effective non-Hermitian physics for degenerate ground states of a nonHermitian Ising model with $\mathcal{RT}$ symmetryJournal-ref: EPL, 128 (2019) 41001Subjects: Statistical Mechanics (cond-mat.stat-mech); Quantum Physics (quant-ph)
In this paper, based on a one-dimensional non-Hermitian spin model with $\mathcal{RT}$-invariant term, we study the non-Hermitian physics for the two (nearly) degenerate ground states. By using the high-order perturbation method, an effective pseudo-spin model is obtained to describe non-Hermitian physics for the two (nearly) degenerate ground states, which are precisely consistent with the numerical calculations. We found that there may exist effective (anti) $\mathcal{PT}$ symmetry for the effective pseudo-spin model of the two (nearly) degenerate ground states. In particular, there exists spontaneous (anti) $\mathcal{PT}$ -symmetry breaking for the topological degenerate ground states with tunable parameters in external fields. We also found that even a very tiny imaginary external field applied will drive $\mathcal{PT}$ phase transition.
- arXiv:2003.10106 [pdf, ps, other]
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Title: Entanglement propagation in thermalization of an isolated quantum systemComments: 7 pages, 4 figuresSubjects: Quantum Physics (quant-ph); Quantum Gases (cond-mat.quant-gas); Statistical Mechanics (cond-mat.stat-mech)
We study dynamics of entanglement in the thermalization process of an isolated quantum many-body system. We propose a simple setup for measuring the propagation speed of entanglement entropy (EE) in numerical simulations and apply it to the integrable/non-integrable spin models in 1D - the transverse Ising (TI) model, the chaotic Ising (CI) model, and the extended chaotic Ising (ECI) model. We find that two distinct time-scales $t^\ast$ and $t_{\rm diff}$ arise in the dynamics of EE in the thermalization process: the former represents the time-scale for the saturation of EE and the latter characterizes spreading of EE over the entire system. Evaluating the propagation speed of entanglement from $t_{\rm diff}$, we find that entanglement propagates ballistically with a constant velocity irrespective of the integrability of the model. The propagation speed of entanglement is found to coincide with the maximum group velocity of quasi-particle excitations in the TI model. We also evaluate the propagation speed of entanglement by mutual information and find that it agrees well with the one evaluated by EE. We discuss the condition for thermalization based on the numerical results and propose that scrambling of the entire system has to take place before saturation of EE for thermalization.
- arXiv:2003.10108 [pdf, other]
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Title: Gate-tunable trion switch for excitonic device applicationsSubjects: Applied Physics (physics.app-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Trions are excitonic species with a positive or negative charge, and thus, unlike neutral excitons, the flow of trions can generate a net detectable charge current. Trions under favourable doping conditions can be created in a coherent manner using resonant excitation. In this work, we exploit these properties to demonstrate a gate controlled trion switch in a few-layer graphene/monolayer WS2/monolayer graphene vertical heterojunction. By using a high resolution spectral scan through a temperature controlled variation of the bandgap of the WS2 sandwich layer, we obtain a gate voltage dependent vertical photocurrent strongly relying on the spectral position of the excitation, and the photocurrent maximizes when the excitation energy is resonant with the trion peak position. Further, the resonant photocurrent thus generated can be effectively controlled by a back gate voltage applied through the incomplete screening of the bottom monolayer graphene, and the photocurrent strongly correlates with the gate dependent trion intensity, while the non-resonant photocurrent exhibits only a weak gate dependence -unambiguously proving a trion driven photocurrent generation under resonance. We estimate a sub-100 fs switching time of the device. The findings are useful towards demonstration of ultra-fast excitonic devices in layered materials.
- arXiv:2003.10110 [pdf, other]
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Title: Thermodynamic cost of synchronizing a population of beating ciliaComments: 6 pages, 3 figuresSubjects: Statistical Mechanics (cond-mat.stat-mech); Biological Physics (physics.bio-ph)
Synchronization among arrays of beating cilia is one of the emergent phenomena in biological processes at meso-scopic scales. Strong inter-ciliary couplings modify the natural beating frequencies, $\omega$, of individual cilia to produce a collective motion that moves around a group frequency $\omega_m$. Here we study the thermodynamic cost of synchronizing cilia arrays by mapping their dynamics onto a generic phase oscillator model. The model suggests that upon synchronization the mean heat dissipation rate is decomposed into two contributions, dissipation from each cilium's own natural driving force and dissipation arising from the interaction with other cilia, the latter of which can be interpreted as the one produced by a potential with a time-dependent protocol in the framework of our model. The spontaneous phase-synchronization of beating dynamics of cilia induced by strong inter-ciliary coupling is always accompanied with a significant reduction of dissipation for the cilia population, suggesting that organisms as a whole expend less energy by attaining a temporal order. At the level of individual cilia, however, a population of cilia with $|\omega|< \omega_m$ expend more amount of energy upon synchronization.
- arXiv:2003.10117 [pdf, ps, other]
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Title: Sign reversal of nonlocal response due to electron collisionsAuthors: K. E. NagaevComments: 4 pages, 4 figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Electron-electron collisions are known to cause a nonlocal voltage drop in a presence of current flow. The semi-phenomenological theory predicts this drop to be opposite to the direction of the current in the ballistic regime. We use a microscopic approach and show that the sign of this drop may be of both signs depending on the temperature and the distance between the source and probe contacts. The change of sign corresponds to the change of the dominant scattering process from head-on collisions to backward scattering of electrons. Our results agree with the experimental data.
- arXiv:2003.10119 [pdf]
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Title: Giant enhancement in the thermal responsivity of microelectromechanical resonators by internal mode couplingComments: 4 figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Instrumentation and Detectors (physics.ins-det)
We report on a giant enhancement in the thermal responsivity of the doubly-clamped GaAs microelectromechanical (MEMS) beam resonators by using the internal mode coupling effect. This is achieved by coupling the fundamental bending mode with the fundamental torsional mode of the MEMS beam resonators through the cubic Duffing nonlinearity. In the mode coupling regime, we have found that, when the input heat to the MEMS resonators is modulated at a particular frequency, the resonance frequency shift caused by heating can be enhanced by almost two orders of magnitude. The observed effect is promising for realizing high-sensitivity thermal sensing by using MEMS resonators, such as ultrasensitive terahertz detection at room temperature.
- arXiv:2003.10124 [pdf]
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Title: Apollonian EmulsionsComments: 6 pages, 7 figuresJournal-ref: EPL 130 38001 (2020)Subjects: Soft Condensed Matter (cond-mat.soft)
We have discovered the existence of extremely polydisperse High Internal-Phase-Ratio Emulsions (HIPE) in which the internal-phase droplets, present at 95% volume fraction, remain spherical and organize themselves in the available space according to Apollonian packing rules. Such Apollonian emulsions are obtained from dispersing oil dropwise in water in the presence of very little surfactant, and allowing them to evolve at rest for a week. The packing structure of the droplets was confirmed through size distribution measurements that evolved spontaneously towards power laws with the known Apollonian exponents, as well as comparison of the structure factors of aged HIPEs measured by Small-Angle X-ray Scattering with that of a numerically simulated Random Apollonian Packing. Thanks to the perfect sphericity of the droplets, Apollonian emulsions were found to display Newtonian ow even at such extremely high volume fraction. We argue that these fascinating space-filling assemblies of spherical droplets are a result of coalescence and fragmentation processes obeying simple geometrical rules of conserving total volume and sphericity, minimizing the elastic energy associated with interactions of neighbouring droplets.
- arXiv:2003.10150 [pdf, other]
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Title: On the origin of the giant spin detection efficiency in tunnel barrier based electrical spin detectorComments: 11 pages, 9 figuresSubjects: Applied Physics (physics.app-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Efficient conversion of a spin signal into an electric voltage in mainstream semiconductors is one of the grand challenges of spintronics. This process is commonly achieved via a ferromagnetic tunnel barrier where non-linear electric transport occurs. In this work, we demonstrate that non-linearity may lead to a spin-to-charge conversion efficiency larger than 10 times the spin polarization of the tunnel barrier when the latter is under bias of a few mV. We identify the underlying mechanisms responsible for this remarkably efficient spin detection as the tunnel barrier deformation and the conduction band shift resulting from a change of applied voltage. In addition, we derive an approximate analytical expression for the detector spin sensitivity $P_{\textrm{det}}(V)$. Calculations performed for different barrier shapes show that this enhancement is present in oxide barriers as well as in Schottky tunnel barriers even if the dominant mechanisms differs with the barrier type. Moreover, although the spin signal is reduced at high temperatures, it remains superior to the value predicted by the linear model. Our findings shed light into the interpretation and understanding of electrical spin detection experiments and open new paths to optimize the performance of spin transport devices.
- arXiv:2003.10157 [pdf, other]
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Title: Grain boundary diffusion in CoCrFeMnNi high entropy alloy: kinetic hints towards a phase decompositionAuthors: Marcel Glienke, Mayur Vaidya, K. Gururaj, Lydia Daum, Bengü Tas, Lukasz Rogal, K.G. Pradeep, Sergiy V. Divinski, Gerhard WildeComments: 17 pages, 11 figuresSubjects: Materials Science (cond-mat.mtrl-sci)
Grain boundary self-diffusion of $^{57}$Co, $^{51}$Cr, $^{59}$Fe and $^{54}$Mn in a coarse-grained, single-phase fcc CoCrFeMnNi high entropy alloy is measured in a wide temperature range of 643 to 1273~K in both C- and B-type kinetic regimes after Harrison's classification. The results suggest that the product of the pertinent segregation factors, $s$, and the grain boundary width, $\delta$, is about 0.5~nm for all elements at temperatures $T>800$~K. Whereas one short-circuit contribution is observed at higher temperatures above 800~K, the penetration profiles in the C-type kinetic regime (643 -- 703~K) reveal two distinct contributions that hint towards a phase decomposition at a fraction of high-angle grain boundaries at these temperatures. A correlative microscopy combining transmission Kikuchi diffraction and atom probe tomography manifests formation of neighbouring Ni-Mn-rich and Cr-rich precipitates at a segment of high angle grain boundaries. Transmission electron microscopy revealed an increased dislocation density in the vicinity of such interfaces which is suggested to be a reason of the enhanced diffusion rates at low temperatures for such short circuits.
- arXiv:2003.10171 [pdf]
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Title: VNCB defect as source of single photon emission from hexagonal boron nitrideSubjects: Materials Science (cond-mat.mtrl-sci)
Single photon emitters in 2D hexagonal boron nitride (hBN) have attracted a considerable attention because of their highly intense, stable, and strain-tunable emission. However, the precise source of this emission, in particular the detailed atomistic structure of the involved crystal defect, remains unknown. In this work, we present first-principles calculations of the vibrationally resolved optical fingerprint of the spin-triplet (2)(_^3)B_1 to (1)(_^3)B_1 transition of the VNCB point defect in hBN. Based on the excellent agreement with experiments for key spectroscopic quantities such as the emission frequency and polarization, the photoluminescence (PL) line shape, Huang-Rhys factor, Debye-Waller factor, and re-organization energy, we conclusively assign the observed single photon emission at ~2eV to the VNCB defect. Our work thereby resolves a long-standing debate about the exact chemical nature of the source of single photon emission from hBN and establishes the microscopic understanding necessary for controlling and applying such photons for quantum technological applications.
- arXiv:2003.10190 [pdf, other]
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Title: Curvature function renormalisation, topological phase transitions and multicriticalityComments: 9 pages, 6 figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Statistical Mechanics (cond-mat.stat-mech)
A recently proposed curvature renormalization group scheme for topological phase transitions defines a generic `curvature function' as a function of the parameters of the theory and shows that topological phase transitions are signalled by the divergence of this function at certain parameters, called critical points, in analogy with usual phase transitions. A renormalization group procedure was also introduced as a way of flowing away from the critical point towards a fixed point, where an appropriately defined correlation function goes to zero and topological quantum numbers characterising the phase are easy to compute. In this paper, using an inversion symmetry broken model in one dimension as an example, we show that there are cases where the fixed point and the critical point appear to intersect, which turn out to be multi-critical points and focus on understanding its implications.
- arXiv:2003.10192 [pdf, other]
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Title: The role of interfacial adhesion on minimum wear particle size and roughness evolutionSubjects: Soft Condensed Matter (cond-mat.soft)
Adhesion between two bodies is a key parameter in wear processes. At the macroscale, strong adhesive bonds are known to lead to high wear rates, as observed in clean metal-on-metal contact. Reducing the strength of the interfacial adhesion is then desirable, and techniques such as lubrication and surface passivation are employed to this end. Still, little is known about the influence of adhesion on the microscopic processes of wear. In particular, the effects of interfacial adhesion on the wear particle size and on the surface roughness evolution are not clear, and are therefore addressed here by means of molecular dynamics simulations. We show that, at short timescales, the surface morphology and not the interfacial adhesion strength dictates the minimum size of wear particles. However, at longer timescales, adhesion alters the particle motion and thus the wear rate and the surface morphology.
- arXiv:2003.10202 [pdf]
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Title: Influence of Mode Structure on the Generation of Phononic Frequency CombsComments: 34 pages, 4 figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Pattern Formation and Solitons (nlin.PS)
The mechanical analog of optical frequency combs, phononic frequency combs, has recently been demonstrated in mechanical resonators and has been attributed to coupling between multiple phonon modes. This paper investigates the influence of mode structure on comb generation using a model of two nonlinearly coupled phonon modes. The model predicts that there is only one region within the amplitude-frequency space where combs exist, and this region is a subset of the Arnold tongue that describes a 2:1 autoparametric resonance between the two modes. In addition, the location and shape of the comb region are analytically defined by the resonance frequencies, quality factors, mode coupling strength, and detuning of the driving force frequency from the mechanical resonances, providing clear conditions for comb generation. These results enable comb structure engineering for applications in areas as broad as sensing, communications, and quantum information science.
- arXiv:2003.10207 [pdf]
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Title: Evolution of Griffiths Phase and Critical Behaviour of La1-xPbxMnO3+-y Solid SolutionsSubjects: Materials Science (cond-mat.mtrl-sci)
Polycrystalline La1-xPbxMnO3+-y (x = 0.3, 0.35, 0.4) solid solutions were prepared by solid state reaction method and their magnetic properties have been investigated. Rietveld refinement of X-ray powder diffraction patterns showed that all samples are single phase and crystallized with the rhombohedral structure in the R-3c space group. A second order paramagnetic to ferromagnetic phase transition was observed for all materials. The Griffiths phase (GP), identified from the temperature dependence of the inverse susceptibility, was suppressed by increasing magnetic field and showed a significant dependence on A-site chemical substitution. The critical behaviour of the compounds was investigated near to their Curie temperatures, using intrinsic magnetic field data. The critical exponents (\b{eta}, {\gamma} and {\delta}) are close to the mean-field approximation values for all three compounds. The observed mean-field like behaviour is a consequence of the GP and the formation of ferromagnetic clusters. Long-range ferromagnetic order is established as the result of long-range interactions between ferromagnetic clusters. The magnetocaloric effect was studied in terms of the isothermal entropy change. Our study shows that the material with the lowest chemical substitution (x = 0.3) has the highest potential (among the three compounds) as magnetic refrigerant, owing to its higher relative cooling power (258 J/kg at 5 T field) and a magnetic phase transition near room temperature.
- arXiv:2003.10220 [pdf, ps, other]
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Title: Compressible Baker Maps and Their Inverses. A Memoir for Francis Hayin Ree [ 1936-2020 ]Authors: William Graham HooverComments: 18 pages with ten figures, submitted and accepted for publication 6 March 2020Journal-ref: Computational Methods in Science and Technology, Volume 26(1), 5-13 (2020)Subjects: Chaotic Dynamics (nlin.CD); Statistical Mechanics (cond-mat.stat-mech); History and Philosophy of Physics (physics.hist-ph)
This memoir is dedicated to the late Francis Hayin Ree, a formative influence shaping my work in statistical mechanics. Between 1963 and 1968 we collaborated on nine papers published in the Journal of Chemical Physics. Those dealt with the virial series, cell models, and computer simulation. All of them were directed toward understanding the statistical thermodynamics of simple model systems. Our last joint work is also the most cited, with over 1000 citations, "Melting Transition and Communal Entropy for Hard Spheres", submitted 3 May 1968 and published that October. Here I summarize my own most recent work on compressible time-reversible two-dimensional maps. These simplest of model systems are amenable to computer simulation and are providing stimulating and surprising results.
- arXiv:2003.10221 [pdf, ps, other]
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Title: High-temperature superconductors as ionic metalsAuthors: D. K. SunkoComments: Published on-line by J Supercond Nov Magn as part of Festschrift in honor of T. H. Geballe's 100th birthdaySubjects: Superconductivity (cond-mat.supr-con); Strongly Correlated Electrons (cond-mat.str-el)
High-temperature superconductors are reviewed in light of the fact that their binding energy is ionic. The conducting electrons are dominated by the much larger energy scales coming from ligand Coulomb integrals, including the out-of-plane ones, which are responsible for the Fermi arcs. The historic reinterpretation of Hund's rule from an intraelectronic to a central mean-field effect is applied to compare the cuprates to the pnictides. It is argued that the cuprates conform to the now-standard central-field paradigm, while the generally abandoned intraelectronic mechanism is exceptionally applicable to the pnictides. A non-adiabatic Fermi liquid paradigm is inferred from the phenomenological evidence. Glueless superconductivity is interpreted as the limiting case of Cooper-pair scattering in cuprates when the Cu ion is perfectly rigid.
- arXiv:2003.10240 [pdf]
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Title: Carbon on the nanoscale: Ultrastiffness and unambiguous definition of incompressibilityJournal-ref: Carbon 160, 228-235 (2020)Subjects: Materials Science (cond-mat.mtrl-sci)
In the presented work, the features of mechanical stiffness of carbon nanoparticles (nanodiamonds and fullerenes) in a wide range of sizes are considered. The enhancement of nanodiamonds stiffness (comparing to bulk diamond) is studied and explained in the terms of average bond stiffness $k_0$. It is shown that $k_0$ can be useful in the description of various carbon nanostructures and gives reliable estimates of their incompressibility. Moreover, we found that $k_0$ can be well estimated based only on relaxed atomic geometry.
- arXiv:2003.10253 [pdf, other]
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Title: Higher harmonic generation in interacting bosons in optical latticesComments: 6 pages, 5 figuresSubjects: Quantum Gases (cond-mat.quant-gas)
We study the generation of higher harmonics using intense light field in an interacting bosonic gas loaded in a one-dimensional optical lattice. We find that the strong light pulse can generate reasonably high harmonics in the insulating regime, while the superfluid regime exhibits only a few harmonics. In the insulating regime, the number of harmonics increases with the variation in the strength of the light field. This originates primarily due to the field-driven resonant and non-resonant excitations in the neutral Mott state and their recombination with the ground state. If the repulsive interaction between two atoms ($U$) is close to the strength of the light field ($A_0$), the resonant quasiparticle-quasihole pairs on nearest-neighbor sites, namely dipole states are found to play a dominant role in the generating higher harmonics. However, in the strong-field limit $A_0\gg U$, the nonresonant states where quasiparticle-quasihole pairs are not on nearest-neighbor sites give rise to higher harmonics. We conclude with a possible experimental outlook of the obtained results.
- arXiv:2003.10291 [pdf, other]
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Title: Diffusive dynamics of elongated particles in active colloidal suspensions of motile algaeSubjects: Soft Condensed Matter (cond-mat.soft)
Swimming microorganisms can influence the diffusion of passive particles. The effect of this swimmer-particle interaction depends on different properties, such as the hydrodynamic field of the swimmer and the relative sizes of microorganisms and particles. We investigated an enhancement of the diffusion of silica doublets in a suspension of microalgae Chlamydomonas reinhardtii in a flat capillary. Depending on the concentration of microswimmers, the translational and rotational diffusion constants increase by several orders of magnitude in the presence of the swimming algae. For low concentrations of algae, the doublets exhibit Brownian motion in a fluctuating flow field generated by multiple swimmers. One can observe strong, diffusive transport caused by occasional large displacements. At high swimmer concentration, the algae form dense clusters, where the rotational motion of the doublets shows a subdiffusive behaviour while the translational motion remains diffusive.
- arXiv:2003.10292 [pdf]
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Title: Quantum Spin Hall effect in bilayer graphene heterostructuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Quantum Physics (quant-ph)
Quantization of electrical conductance in condensed matter systems often arises from the presence of edge-modes. These modes are globally protected from local perturbations by certain symmetries of the underlying system. In the case of a time-reversal (TR) invariant 2-dimensional topological insulator (TI) - also known as the Quantum Spin Hall (QSH) insulator state - the bulk of the system is gapped, while the edges host counter-propagating, gapless metallic conducting states of opposite spin polarizations. Realizing TR invariant QSH in intrinsic graphene systems has been elusive so far due to the extremely weak spin-orbit interactions of carbon atoms. In this letter, we report the experimental observation of QSH state in bilayer graphene/single-layer WSe$_2$ heterostructures - a system similar to the one in which the pioneering proposals of Kane and Mele envisaged the QSH insulator state. We find the measured value of electrical conductance to be quantized to the theoretically predicted value of $e^2/h$ for each QSH edge-mode. The linear conductance obtained in several measurement configurations matches precisely with that obtained from a tight-binding model replicating our heterostructure with periodic [for bulk topology] and open-boundary conditions [for topological edge-modes]. Our work provides the pivotal affirmation of the archival Kane - Mele model for QSH state in graphene and expands the material choices for QSH states.
- arXiv:2003.10302 [pdf]
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Title: The collision frequency of electron-neutral-particle in the weakly ionized plasma with the power-law velocity distributionComments: 11 pages, 43 references, 3 figuresJournal-ref: Contrib.Plasma Phys. 60 (2020) e201900183Subjects: Plasma Physics (physics.plasm-ph); Statistical Mechanics (cond-mat.stat-mech)
We study the collision frequency of electron-neutral-particle in the weakly ionized plasma with the power-law velocity q-distribution and derive the formulation of the average collision frequency. We find that the average collision frequency in the q-distributed plasma also depends strongly on the q-parameter and thus is generally different from that in the Maxwell-distributed plasma, which therefore modifies the transport coefficients in the previous studies of the weakly ionized plasmas with the power-law velocity distributions.
- arXiv:2003.10331 [pdf, ps, other]
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Title: Varying Newton constant and black hole to white hole quantum tunnelingAuthors: G.E. VolovikComments: 5 pages, no figuresSubjects: General Relativity and Quantum Cosmology (gr-qc); Other Condensed Matter (cond-mat.other); High Energy Physics - Phenomenology (hep-ph)
The thermodynamics of black holes is discussed for the case, when the Newton constant $G$ is not a constant, but is the thermodynamic variable. This gives for the first law of the Schwarzschild black hole thermodynamics: $dS_\text{BH}= -AdK + \frac{dM}{T_\text{BH}}$, where the gravitational coupling $K=1/4G$, $M$ is the black hole mass, $A$ is the area of horizon, and $T_\text{BH}$ is Hawking temperature. From this first law it follows that the dimensionless quantity $M^2/K$ is the adiabatic invariant, which in principle can be quantized if to follow the Bekenstein conjecture. From the Euclidean action for the black hole it follows that $K$ and $A$ serve as dynamically conjugate variables. This allows us to calculate the quantum tunneling from the black hole to the white hole, and determine the temperature and entropy of the white hole.
- arXiv:2003.10338 [pdf, other]
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Title: Quantum critical thermal transport in the unitary Fermi gasComments: 10 figuresJournal-ref: Phys. Rev. Research 2, 023301 (2020)Subjects: Quantum Gases (cond-mat.quant-gas); Strongly Correlated Electrons (cond-mat.str-el)
Strongly correlated systems are often associated with an underlying quantum critical point which governs their behavior in the finite temperature phase diagram. Their thermodynamical and transport properties arise from critical fluctuations and follow universal scaling laws. Here, we develop a microscopic theory of thermal transport in the quantum critical regime expressed in terms of a thermal sum rule and an effective scattering time. We explicitly compute the characteristic scaling functions in a quantum critical model system, the unitary Fermi gas. Moreover, we derive an exact thermal sum rule for heat and energy currents and evaluate it numerically using the nonperturbative Luttinger-Ward approach. For the thermal scattering times we find a simple quantum critical scaling form. Together, this determines the heat conductivity, thermal diffusivity, Prandtl number and sound diffusivity from high temperatures down into the quantum critical regime. The results provide a quantitative description of recent sound attenuation measurements in ultracold Fermi gases.
- arXiv:2003.10343 [pdf]
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Title: Spin-wave gap collapse in Rh-doped Sr2IrO4Authors: J. Bertinshaw, J. K. Kim, J. Porras, K. Ueda, N. H. Sung, A. Efimenko, A. Bombardi, Jungho Kim, B. Keimer, B. J. KimComments: 5 pages, 3 figuresJournal-ref: Physical Review B, 101, 094428 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el)
We use resonant inelastic x-ray scattering (RIXS) at the Ir L3 edge to study the effect of hole doping upon the Jeff=1/2 Mott-insulating state in Sr2IrO4, via Rh replacement of the Ir site. The spin-wave gap, associated with XY-type spin-exchange anisotropy, collapses with increasing Rh content, prior to the suppression of the Mott-insulating state and in contrast to electron doping via La substitution of the Sr site. At the same time, despite heavy damping, the d-d excitation spectra retain their overall amplitude and dispersion character. A careful study of the spin-wave spectrum reveals that deviations from the J1-J2-J3 Heisenberg used to model the pristine system disappear at intermediate doping levels. These findings are interpreted in terms of a modulation of Ir-Ir correlations due to the influence of Rh impurities upon nearby Ir wave functions, even as the single-band Jeff=1/2 model remains valid up to full carrier delocalization. They underline the importance of the transition metal site symmetry when doping pseudospin systems such as Sr2IrO4.
- arXiv:2003.10349 [pdf, other]
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Title: Hydrodynamic-colloidal interactions of an oil droplet and a membrane surfaceComments: 20 pages, 5 figures; in pressJournal-ref: Langmuir 2020, 36, 11, 2858-2864Subjects: Fluid Dynamics (physics.flu-dyn); Soft Condensed Matter (cond-mat.soft); Chemical Physics (physics.chem-ph)
Understanding the influence of hydrodynamic stresses and colloidal interactions between droplets and membranes will inform better engineered membrane surfaces and process conditions. Using a long-wave hydrodynamic description that incorporates wettability and electrostatic repulsion, we numerically investigate the influence of droplet shapes and membrane characteristics on the overall repulsion-attraction towards the membrane surface. A stability phase diagram classifies stable-unstable drop shapes and investigate whether there is reversible deposition of droplets onto the membrane.
- arXiv:2003.10358 [pdf, other]
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Title: Atomistic perspective of long lifetimes of small skyrmions at room temperatureSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
The current development to employ magnetic skyrmions in novel spintronic device designs has led to a demand for room temperature-stable skyrmions of ever smaller size. We present extensive studies on skyrmion stability in atomistic magnetic systems in two- and three-dimensional geometries. We show that for materials described by the same micromagnetic parameters, the variation of the atomistic exchange between different neighbors, the stacking order, and the number of layers of the atomic lattice can significantly influence the rate of the thermally activated decay of a skyrmion. These factors alone are important considerations, but it is shown that their combination can open up novel avenues of materials design in the search for sub-10nm skyrmions, as their lifetime can be extended by several orders of magnitude.
- arXiv:2003.10361 [pdf, ps, other]
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Title: Nodal Semimetals: A Survey on Optical ConductivityComments: to appear in a special issue of pss(b) on topological materialsSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Among different topological and related phases of condensed matter, nodal semimetals occupy a special place - the electronic band topology in these materials is related to three-dimensional bulk, rather than to surface, states. A great variety of different realizations of electronic band crossings (the nodes) leads to a plethora of different electronic properties, ranging from the chiral anomaly to solid-state realizations of a black-hole horizon. The different nodal phases have similar low-energy band structure and quasiparticle dynamics, which both can be accessed experimentally by a number of methods. Optical measurements with their large penetration depth and high energy resolution are ideally suited as such a bulk probe; especially at low energies where other spectroscopic methods often lack the required resolution. In this contribution, we review recent optical-conductivity studies of different nodal semimetals, discuss possible limitations of such measurements, and provide a comparison between the experimental results, simple theoretical models, and band-structure-based calculations.
- arXiv:2003.10364 [pdf]
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Title: Optical-Field Driven Charge-Transfer Modulations near Composite NanostructuresAuthors: Kwang Jin Lee, Elke Beyreuther, Sohail A. Jalil, Sang Jun Kim, Lukas Eng, Chunlei Guo, Pascal AndreComments: 8 pages, 6 figuresSubjects: Materials Science (cond-mat.mtrl-sci); Soft Condensed Matter (cond-mat.soft); Chemical Physics (physics.chem-ph)
Optical activation of material properties illustrates the potentials held by tuning light-matter interactions with impacts ranging from basic science to technological applications. Here, we demonstrate for the first time that composite nanostructures providing nonlocal environments can be engineered to optically trigger photoinduced charge transfer dynamic (CTD) modulations in the solid state. The nanostructures herein explored lead to unprecedented out-of-phase behaviour between charge separation and recombination dynamics, along with linear CTD variations with the optical-field amplitude. Using transient absorption spectroscopy, up to 270 % increase in charge separation rate is obtained in organic semiconductor thin films. We provide evidences that composite nanostructures allow for surface photovoltages to be created, which kinetics vary with the composite architecture and last beyond optical pulse temporal characteristics. Furthermore, by generalizing Marcus theory framework, we explain why CTD modulations can only be unveiled when optic field effects are enhanced by nonlocal image dipole interactions. Demonstrating that composite nanostructures can be designed to use optical fields as CTD remote actuators opens the path for their use in practical and original applications ranging from photochemistry to optoelectronics.
- arXiv:2003.10371 [pdf, ps, other]
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Title: Nonperturbative Dyson-Schwinger equation approach to strongly interacting Dirac fermion systemsComments: 37 pages, discussions addedSubjects: Strongly Correlated Electrons (cond-mat.str-el); Materials Science (cond-mat.mtrl-sci); Statistical Mechanics (cond-mat.stat-mech)
Studying the strong correlation effects in interacting Dirac fermion systems is one of the most challenging problems in modern condensed matter physics. The long-range Coulomb interaction and the fermion-phonon interaction can play an important role in such systems, and in some cases may lead to a variety of intriguing properties, including non-Fermi liquid behavior and phase-transition instabilities. In the strong-coupling regimes, the method of weak-coupling expansion breaks down. Here, we investigate the interaction between massless Dirac fermions and a generic scalar bosonic mode, and develop an efficient non-perturbative approach to access the strong-coupling regime. This approach is universal and applicable to both (1+2) and (1+3) dimensions. We first derive a number of coupled Ward-Takahashi identities based on symmetry analysis, and then use these identities to express the fermion-boson vertex function as a linear combination of fully renormalized fermion propagators. Based on these results, we rigorously prove that the fully renormalized fermion propagator satisfies an exact and self-closed Dyson-Schwinger integral equation, which can be directly solved by numerical skills. Our approach provides a unified framework for the self-consistent investigation of the interaction-induced effects, including Landau damping, fermion velocity renormalization, and formation of charge density wave. All such effects are extracted from the solutions of integral equations, thus there is no need to perform perturbative expansion and all the results are reliable no matter how strong the interaction is. Our approach can be used to treat the strong long-range Coulomb interaction and the strong fermion-phonon interaction. See main paper for full Abstract.
- arXiv:2003.10382 [pdf, ps, other]
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Title: Thermal equilibration on the edges of topological liquidsComments: 6 pages, 1 figureSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Thermal conductance has emerged as a powerful probe of topological order in the quantum Hall effect and beyond. The interpretation of experiments crucially depends on the ratio of the sample size and the equilibration length, on which energy exchange among contra-propagating chiral modes becomes significant. We show that at low temperatures the equilibration length diverges as $1/T^2$ for almost all Abelian and non-Abelian topological orders. A faster $1/T^4$ divergence is present on the edges of the non-Abelian PH-Pfaffian and negative-flux Read-Rezayi liquids. We address experimental consequences of the $1/T^2$ and $1/T^4$ laws in a sample, shorter than the equilibration length.
- arXiv:2003.10387 [pdf, other]
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Title: Chaos-assisted tunneling resonances in a synthetic Floquet superlatticeAuthors: M. Arnal, G. Chatelain, M. Martinez, N. Dupont, O. Giraud, D. Ullmo, B. Georgeot, G. Lemarié, J. Billy, D. Guéry-OdelinSubjects: Quantum Gases (cond-mat.quant-gas); Quantum Physics (quant-ph)
The field of quantum simulation, which aims at using a tunable quantum system to simulate another, has been developing fast in the past years as an alternative to the all-purpose quantum computer. In particular, the use of temporal driving has attracted a huge interest recently as it was shown that certain fast drivings can create new topological effects, while a strong driving leads to e.g. Anderson localization physics. In this work, we focus on the intermediate regime to observe a quantum chaos transport mechanism called chaos-assisted tunneling which provides new possibilities of control for quantum simulation. Indeed, this regime generates a rich classical phase space where stable trajectories form islands surrounded by a large sea of unstable chaotic orbits. This mimics an effective superlattice for the quantum states localized in the regular islands, with new controllable tunneling properties. Besides the standard textbook tunneling through a potential barrier, chaos-assisted tunneling corresponds to a much richer tunneling process where the coupling between quantum states located in neighboring regular islands is mediated by other states spread over the chaotic sea. This process induces sharp resonances where the tunneling rate varies by orders of magnitude over a short range of parameters. We experimentally demonstrate and characterize these resonances for the first time in a quantum system. This opens the way to new kinds of quantum simulations with long-range transport and new types of control of quantum systems through complexity.
- arXiv:2003.10390 [pdf, other]
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Title: Generalized $f$-Sum Rules and Kohn formulas on Non-linear ConductivitiesComments: 8 pages, 1 figure. This work supersedes our previous submission arXiv:1907.01212 with substantial new resultsSubjects: Strongly Correlated Electrons (cond-mat.str-el); Other Condensed Matter (cond-mat.other); Quantum Gases (cond-mat.quant-gas); Statistical Mechanics (cond-mat.stat-mech)
The $f$-sum rule and the Kohn formula are well-established general constraints on the electric conductivity in quantum many-body systems. We present their generalization to non-linear conductivities at all orders of the response in a unified manner, by considering two limiting quantum time-evolution processes: a quench process and an adiabatic process. Our generalized formulas are valid in any stationary state, including the ground state and finite temperature Gibbs states, regardless of the details of the system such as the specific form of the kinetic term, the strength of the many-body interactions, or the presence of disorders.
- arXiv:2003.10394 [pdf, other]
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Title: Orientational Distribution of an Active Brownian Particle: an analytical studyAuthors: Supurna SinhaComments: Submitted for publication; three figures added; references addedSubjects: Statistical Mechanics (cond-mat.stat-mech)
We use the Fokker Planck equation as a starting point for studying the orientational probability distribution of an Active Brownian Particle (ABP) in $(d+1)$ dimensions. This Fokker Planck equation admits an exact solution in series form which is, however, unwieldly to use because of poor convergence for short and intermediate times. A truncated version of this series is a reasonable approximation for long times. In this paper, we present an analytical closed form expression, which gives a good approximate orientational probability distribution, which is derived using saddle point methods for short times. However, it works well even for intermediate times. Thus, we have simple analytical forms for the ${\it entire}$ range of time scales for the orientational probability distribution of an ABP. Our predictions can be tested against future experiments and simulations probing orientational probability distribution of an ABP.
- arXiv:2003.10417 [pdf, other]
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Title: Fully Anharmonic, Non-Perturbative Theory of Vibronically Renormalized Electronic Band StructuresSubjects: Materials Science (cond-mat.mtrl-sci)
We develop a first-principles approach for the treatment of vibronic interactions in solids that overcomes the main limitations of state-of-the-art electron-phonon coupling formalisms. In particular, anharmonic effects in the nuclear dynamics are accounted to all orders via ab initio molecular dynamics simulations. This non-perturbative, self-consistent approach evaluates the response of the wave functions along the computed anharmonic trajectory; thus it fully considers the coupling between nuclear and electronic degrees of freedom. We validate and demonstrate the merits of the concept by calculating temperature-dependent, momentum-resolved spectral functions for silicon and the cubic perovskite SrTiO3, a strongly anharmonic material featuring soft modes. In the latter case, our approach reveals that anharmonicity and higher-order vibronic couplings contribute substantially to the electronic-structure at finite-temperatures, noticeably affecting band gaps and effective masses, and hence macroscopic properties such as transport coefficients.
- arXiv:2003.10418 [pdf, ps, other]
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Title: Monopole-limited nucleation of magnetism in Eu$_{2}$Ir$_{2}$O$_{7}$Comments: 9 pages, 4 figuresJournal-ref: Phys. Rev. B 101, 174435 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el)
We present an in-depth analysis of muon-spin spectroscopy measurements of Eu$_{2}$Ir$_{2}$O$_{7}$ under the effect of the Eu$_{1-x}$Bi$_{x}$ isovalent and diamagnetic substitution as well as of external pressure. Our results evidence an anomalously slow increase of the magnetic volume fraction upon decreasing temperature only for stoichiometric Eu$_{2}$Ir$_{2}$O$_{7}$, pointing towards highly unconventional properties of the magnetic phase developing therein. We argue that magnetism in Eu$_{2}$Ir$_{2}$O$_{7}$ develops based on the nucleation of magnetic droplets at $T_{N}$, whose successive growth is limited by the need of a continuous generation of magnetic hedgehog monopoles.
- arXiv:2003.10426 [pdf]
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Title: Towards Chemical Kinetics for Operando Electron Microscopy of Catalysts: 3D Modeling of Gas and Temperature Distributions During Catalytic ReactionsSubjects: Materials Science (cond-mat.mtrl-sci)
$\textit{In situ}$ environmental transmission electron microscopy (ETEM) is a powerful tool for observing structural modifications taking place in heterogeneous catalysts under reaction conditions. However, to strengthen the link between catalyst structure and functionality, an $\textit{operando}$ measurement must be performed in which reaction kinetics and catalyst structure are simultaneously determined. To determine chemical kinetics for gas-phase catalysis, it is necessary to develop a reliable chemical engineering model to describe catalysis as well as heat and mass transport processes within the ETEM cell. Here, we establish a finite element model to determine the gas and temperature profiles during catalysis in the ETEM. The model is applied to a $SiO_2$-supported Ru catalyst performing CO oxidation. Good agreement is achieved between simulated conversions and those measured experimentally across a temperature range of 25 - 350 {\deg}C. In general, the simulations show that the temperature and gas are relatively homogeneous within the hot zone of the TEM holder where the catalyst is located. The uniformity of gas and temperature across the catalyst indicates that the ETEM reactor system behavior approximates that of a continuously stirred tank reactor. These findings indicate that one can reliably evaluate the temperature and steady-state reaction rate of the catalyst that is imaged during an operando electron microscopy experiment.
- arXiv:2003.10430 [pdf]
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Title: Tracking ultrafast solid-state dynamics using high harmonic spectroscopyAuthors: Mina R. Bionta, Elissa Haddad, Adrien Leblanc, Vincent Gruson, Philippe Lassonde, Heide Ibrahim, Jérémie Chaillou, Nicolas Émond, Martin R. Otto, Bradley J. Siwick, Mohamed Chaker, François LégaréComments: 20 pages and 4 figures main text, 8 pages and 4 figures supplementary informationSubjects: Optics (physics.optics); Materials Science (cond-mat.mtrl-sci)
We establish time-resolved high harmonic generation (tr-HHG) as a powerful spectroscopy for photoinduced dynamics in strongly correlated materials through a detailed investigation of the insulator-to-metal transitions in vanadium dioxide. We benchmark our technique by comparing our measurements to established momentum-resolved ultrafast electron diffraction, and theoretical density functional calculations. Tr-HHG allows distinguishing of individual dynamic channels, including a transition to a thermodynamically hidden phase. In addition, the HHG yield is shown to be modulated at a frequency characteristic of a coherent phonon in the equilibrium monoclinic phase over a wide range of excitation fluences. These results demonstrate that tr-HHG is capable of tracking complex dynamics in solids through its sensitivity to the band structure.
Replacements
- arXiv:1409.6389 (replaced) [pdf, ps, other]
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Title: Spin filter of electrons through a zeeman splitting single quantum dotComments: 7 pages, 8 figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Electron spin filter induced by Zeeman splitting in a few-electron quantum dot coupled to two normal electrodes is studied considering Coulomb blockade effect. Based on the Anderson model and Liouville-von Neumann equation, equation of motion of the system is derived and analytical solutions are achieved. Transport windows for perfectly polarized current, partially polarized current and non-polarized current induced by the Zeeman splitting energy and Coulomb blockade potential are exploited. We will give the relations of voltage, magnetic field and temperature for high quality spin filtering.
- arXiv:1604.07144 (replaced) [pdf]
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Title: Effects of the Electronic Structure, Phase Transition and Localized Dynamics of Atoms in the Formation of Tiny Particles of GoldSubjects: Materials Science (cond-mat.mtrl-sci)
In addition to the self-governing properties, tiny-sized particles of metallic colloids are the building blocks of large-sized particles. This topic has been the subject of many studies. The development of a tiny-sized particle on the solution surface depends on the attained dynamics of atoms. When nano-energy supplied to the transitional behavior atoms of monolayer assembly, atoms bound in the shape and size of nano-energy. In such tiny particles, atoms of arrays can elongate uniformly to form structures of smooth elements. Impinging electron streams at a fixed angle can result in elongating further the already elongated atoms of arrays. Travelling photons along the air-solution interface can further shape arrays of elongated atoms through forcing energy. Inside the solution or near the air-solution interface, gold atoms also develop tiny particles of different features, where in addition to their attained dynamics, miscellaneous factors also contribute. Here, atoms in groups can bind to form a tiny-sized particle. In the formation process of 3rd type of tiny particle, amalgamated atoms can bind through the execution of inter-state electron dynamics. This study highlights the fundamental process of formation of different tiny-sized particles, where electronic structure, phase transition and localized dynamics of gold atoms exert influence in different manners. Such a tool of processing materials opens several possibilities to develop materials...
- arXiv:1609.08047 (replaced) [pdf]
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Title: Tiny-Shaped Particles Developing Mono Layer Shape Dealing with Localized Gravity in Solution SurfaceAuthors: Mubarak AliSubjects: Materials Science (cond-mat.mtrl-sci)
In different materials, orientationally controlled assembling of building blocks results in the development of nanoparticles and particles of geometrical shapes. Coalescences of tiny particles to a larger particle is pronounced in atoms of metallic behavior. In the developmental process of nanoparticles and particles, atoms configure in monolayer assembly at first place where they mainly deal with re-crystallization state. At air-solution interface, when triangle-shaped packets of nano-energy were supplied to atoms of compact monolayer assembly, atoms bound in the shape and size of nano-energy. Blocks of joined triangular shaped tiny particles developed when tuned bipolar pulses were examined. On the exertion of uneven force to electrons of atoms at contact point, a block of joined tiny-sized particles separated into two tiny particles of equilateral triangular shape. On electronically flat solution surface, atoms of tiny particles in re-crystallization state elongate at equal rate. From the centre of each transitional behavior atom, electrons of east-west poles deal with the even exertion of surface force along their opposite poles. Thus, arrays of bound atoms formed a tiny-shaped particle developed in its structures of smooth elements. Such structures of smooth elements flatten by the forced energy of traveled photons along the air-solution interface. Originally, binding of solid atoms in neutral state is to be anticipated under the execution of confined inter-state electron dynamics, where they possess ground point below the ground surface. Nevertheless, such developed tiny particles come from suitable zones of solution surface; they pack through the assembling of their structures of smooth elements to develop a shaped mono layer of developing nanoparticle or particle in geometrical shape. In solution surface, a shaped mono layer adheres to the underneath shaped mono layer...
- arXiv:1611.01255 (replaced) [pdf]
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Title: Structure Evolution in Atoms of Those Elements Executing Confined Inter-State Electron DynamicsAuthors: Mubarak AliSubjects: Materials Science (cond-mat.mtrl-sci)
A structure evolution in original format of exerting force at electron level in atoms of gas, semi-solid and solid behaviors does not obey the conventional insights falling under the Bravais crystal systems. This study deals with structure evolutions in atoms of those elements executing confined inter-state dynamics of their electrons. A structure gets evolved on amalgamation of atoms due to significantly attained dynamics. Structures evolve in different formats of exerting forces as per mechanism of electron dynamics in their atoms. In the neutral state, atoms transform heat energy into binding energy having shapes like tick, integral or Gaussian distribution symbol. The shape of binding energy depends on the inter-state gap of filled to unfilled state, which is related to outer ring in an atom. The evolving structure of atoms having identical ground points deals with forced exertions to suitable electrons at the same level, too. In atoms of space format, the structure evolves above the suitable level of ground surface. In atoms of grounded format, the structure evolves below the suitable level of ground surface. Dimensions of evolving structure depend on the number of electrons in the outer ring (of an atom) executing dynamics. When the execution of inter-state dynamics is only for one electron, one-dimensional structure is evolved. When the execution of inter-state dynamics is for two electrons, two-dimensional structure is evolved. In the atoms of those elements where three electrons of their outer rings simultaneously execute dynamics, a bit complex mechanism of structure evolution in those atoms is observed. An atom binds to the targeted atom at the points of their generated energy. In the structure evolution of space format and grounded format, amalgamating atoms bind to...
- arXiv:1611.05392 (replaced) [pdf]
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Title: Atoms of None of the Elements Ionize While Atoms of Inert Behavior Split by Photonic CurrentAuthors: Mubarak AliSubjects: Materials Science (cond-mat.mtrl-sci)
The phenomenon whereby atoms deal with the positive or negative charge by losing or gaining the electron forms the basis of familiar processes. In the elements where atoms comprise unfilled states, they are eligible to execute electron dynamics indicating that they do not ionize. At suitable level of ground surface, atoms of solid and gas both deal with transitional behaviors as per engaged force under involved energy. Transitional behaviors of such atoms are based on infinitesimal displacements of electrons. So, electrons remain clamped within their energy knots. In inert gas atoms, a different mechanism is involved. Under the excessive population of photons, inert behavior atoms split distorting into the electron (streams). As a result, progressing photons of forcing energy leave distorting inter-state electron gaps of splitting atoms entering the air medium. Hence, characteristics of photons under lowered forcing energy become obvious to reveal the glow of light known as plasma. On splitting inert gas atoms, their electrons carry forcing energy of chasing photons. When forced energy electrons impinge on underneath elongated atoms of solid at suitable inclination, they elongate them further. When carrying forced energy electrons do not impinge at suitable inclination, instead of elongating those atoms further, impinging electrons deform them by enabling non-orientationally based stretching of energy knots. The splitting of inert gas atoms into electrons, carrying of photons by electrons to impinge and the phenomenon of light glow reveal that photonic current is a source of power rather than electric current. As per set feature, a microscopic analysis is due to the resolving power of working photons. So, a photonic current is due to photonic propagation, where a consistent inter-state electron gap of structure is...
- arXiv:1806.06677 (replaced) [pdf, other]
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Title: Bulk-Boundary Correspondence for Topological Insulators with Quantized Magneto-Electric EffectComments: 29 pages, 6 figures; final version submitted for journal publicationJournal-ref: J. Phys. A: Math. Theor. 53, 205203 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el); Mathematical Physics (math-ph)
We study bulk-boundary correspondences and related surface phenomena stabilized by the second Chern number in three-dimensional insulators driven in adiabatic cycles. Magnetic fields and disorder effects are incorporated in our analysis using operator algebraic methods. We use the connecting maps between the $K$-theories of bulk and boundary algebras as engines for the bulk-boundary correspondences. We discovered that both the exponential and the index connecting maps are relevant for the context considered here as they lead to distinct experimentally observable surface phenomena, such as pumping and transfer of quantum surface Hall states or proximity induced Hall effect. The surface Hall physics of time-reversal symmetric topological insulators is also investigated using the new tools, which can model irrational magnetic fluxes and arbitrary large surface disorder.
- arXiv:1808.05656 (replaced) [pdf, other]
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Title: Classification of symmetry-protected topological many-body localized phases in one dimensionComments: Version to appear in Journal of Physics: Condensed MatterJournal-ref: J. Phys.: Cond. Mat. 32, 305601 (2020)Subjects: Disordered Systems and Neural Networks (cond-mat.dis-nn)
We provide a classification of symmetry-protected topological (SPT) phases of many-body localized (MBL) spin and fermionic systems in one dimension. For spin systems, using tensor networks we show that all eigenstates of these phases have the same topological index as defined for SPT ground states. For unitary on-site symmetries, the MBL phases are thus labeled by the elements of the second cohomology group of the symmetry group. A similar classification is obtained for anti-unitary on-site symmetries, time-reversal symmetry being a special case with a $\mathbb{Z}_2$ classification (cf. [Phys. Rev. B 98, 054204 (2018)]). For the classification of fermionic MBL phases, we propose a fermionic tensor network diagrammatic formulation. We find that fermionic MBL systems with an (anti-)unitary symmetry are classified by the elements of the (generalized) second cohomology group if parity is included into the symmetry group. However, our approach misses a $\mathbb{Z}_2$ topological index expected from the classification of fermionic SPT ground states. Finally, we show that all found phases are stable to arbitrary symmetry-preserving local perturbations. Conversely, different topological phases must be separated by a transition marked by delocalized eigenstates. Finally, we demonstrate that the classification of spin systems is complete in the sense that there cannot be any additional topological indices pertaining to the properties of individual eigenstates, but there can be additional topological indices that further classify Hamiltonians.
- arXiv:1810.02300 (replaced) [pdf, other]
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Title: Anisotropic electrical and thermal magnetotransport in the magnetic semimetal GdPtBiAuthors: Clemens Schindler, Stanislaw Galeski, Walter Schnelle, Rafał Wawrzyńczak, Wajdi Abdel-Haq, Satya N. Guin, Johannes Kroder, Nitesh Kumar, Chenguang Fu, Horst Borrmann, Chandra Shekhar, Claudia Felser, Tobias Meng, Adolfo G. Grushin, Yang Zhang, Yan Sun, Johannes GoothComments: 11 figuresJournal-ref: Phys. Rev. B 101, 125119 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Theory (hep-th)
The half-Heusler rare-earth intermetallic GdPtBi has recently gained attention due to peculiar magnetotransport phenomena that have been associated with the possible existence of Weyl fermions, thought to arise from the crossings of spin-split conduction and valence bands. On the other hand, similar magnetotransport phenomena observed in other rare-earth intermetallics have often been attributed to the interaction of itinerant carriers with localized magnetic moments stemming from the $4f$-shell of the rare-earth element. In order to address the origin of the magnetotransport phenomena in GdPtBi, we performed a comprehensive study of the magnetization, electrical and thermal magnetoresistivity on two single-crystalline GdPtBi samples. In addition, we performed an analysis of the Fermi surface via Shubnikov-de Haas oscillations in one of the samples and compared the results to \emph{ab initio} band structure calculations. Our findings indicate that the electrical and thermal magnetotransport in GdPtBi cannot be solely explained by Weyl physics and is strongly influenced by the interaction of both itinerant charge carriers and phonons with localized magnetic Gd-ions and possibly also paramagnetic impurities.
- arXiv:1812.04842 (replaced) [pdf, other]
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Title: Calculated Curie temperatures for rare-earth permanent magnets: ab initio inspection on localized magnetic moments in d-electron ferromagnetismComments: 5 pages, 7 figures, to be published on Phys. Rev. BJournal-ref: Phys. Rev. B 101, 144402 (2020)Subjects: Materials Science (cond-mat.mtrl-sci)
We present a data set of calculated Curie temperatures for the main-phase compounds of rare-earth permanent magnets. We employ ab initio electronic structure calculations for the itinerant ferromagnetism and an effective spin model for the finite-temperature magnetism. Curie temperatures are derived on the basis of a classical Heisenberg model mapped via Liechtenstein's formula for atomic-pair-wise exchange couplings. Relative trends with respect to the species of rare-earth elements in calculated Curie temperatures for R2Fe14B are in agreement with experimental trends. Quantitative comparison between calculation and experimental data found in the literature point to an effective range of the exchange couplings imposing a limit on the validity range of the effective spin model.
- arXiv:1812.05086 (replaced) [pdf, other]
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Title: Arbitrary Lagrangian--Eulerian finite element method for curved and deforming surfaces. I. General theory and application to fluid interfacesComments: 59 pages, 16 figuresJournal-ref: Journal of Computational Physics 407 (2020) 109253Subjects: Computational Physics (physics.comp-ph); Soft Condensed Matter (cond-mat.soft); Biological Physics (physics.bio-ph); Fluid Dynamics (physics.flu-dyn)
An arbitrary Lagrangian--Eulerian (ALE) finite element method for arbitrarily curved and deforming two-dimensional materials and interfaces is presented here. An ALE theory is developed by endowing the surface with a mesh whose in-plane velocity need not depend on the in-plane material velocity, and can be specified arbitrarily. A finite element implementation of the theory is formulated and applied to curved and deforming surfaces with in-plane incompressible flows. Numerical inf--sup instabilities associated with in-plane incompressibility are removed by locally projecting the surface tension onto a discontinuous space of piecewise linear functions. The general isoparametric finite element method, based on an arbitrary surface parametrization with curvilinear coordinates, is tested and validated against several numerical benchmarks. A new physical insight is obtained by applying the ALE developments to cylindrical fluid films, which are computationally and analytically found to be stable to non-axisymmetric perturbations, and unstable with respect to long-wavelength axisymmetric perturbations when their length exceeds their circumference. A Lagrangian scheme is attained as a special case of the ALE formulation. Though unable to model fluid films with sustained shear flows, the Lagrangian scheme is validated by reproducing the cylindrical instability. However, relative to the ALE results, the Lagrangian simulations are found to have spatially unresolved regions with few nodes, and thus larger errors.
- arXiv:1812.07245 (replaced) [pdf, other]
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Title: Low-energy optical phonons induce glassy-like vibrational and thermal anomalies in ordered crystalsJournal-ref: J. Phys. Mater. 3, 015004 (2020)Subjects: Materials Science (cond-mat.mtrl-sci); Soft Condensed Matter (cond-mat.soft)
It is widely accepted that structural glasses and disordered crystals exhibit anomalies in the their thermal, mechanical and acoustic properties as manifestations of the breakdown of the long-wavelength approximation in a disordered dissipative environment. However, the same type of glassy-like anomalies (i.e. boson peak in the vibrational density of states (VDOS) above the Debye level, peak in the normalized specific heat at $T\simeq10 K$ etc) have been recently observed also in perfectly ordered crystals, including thermoelectric compounds. Here we present a theory that predicts these surprising effects in perfectly ordered crystals as a result of low-lying (soft) optical phonons. In particular, it is seen that a strong boson peak anomaly (low-energy excess of modes) in the VDOS can be due almost entirely to the presence of low-energy optical phonons, provided that their energy is comparable to that of the acoustic modes at the Brillouin zone boundary. The boson peak is predicted also to occur in the heat capacity at low $T$. In presence of strong damping (which might be due to anharmonicities in the ordered crystals), these optical phonons contribute to the low-$T$ deviation from Debye's $T^{3}$ law, producing a linear-in-$T$ behavior which is typical of glasses, even though no assumptions of disorder whatsoever are made in the model. These findings are relevant for understanding and tuning thermal transport properties of thermoelectric compounds, and possibly for the enhancement of electron-phonon superconductivity.
- arXiv:1812.09948 (replaced) [pdf, other]
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Title: Matter-wave interferometry using a levitated magnetic nanoparticleAuthors: A T M Anishur RahmanSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Quantum Physics (quant-ph)
The superposition principle is one of the bizarre predictions of quantum mechanics. Nevertheless, it has been experimentally verified using electrons, photons, atoms, and molecules. In this article, using a $20~$nm levitated ferromagnetic FePt nanoparticle, an exotic all optical spin polarization technique and the matter-wave interferometry, we show that a mesoscopic spatial Schrodinger cat can be created. Additionally, we argue that the maximum spatial separation between the delocalized wavepackets can be $25~\mu m$ and is significantly larger than the object itself.
- arXiv:1901.00019 (replaced) [pdf, other]
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Title: One-dimensional few-electron effective Wigner crystal in quantum and classical regimesComments: Updated final published versionJournal-ref: Phys. Rev. B 101, 125113 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Strongly Correlated Electrons (cond-mat.str-el)
A system of confined charged electrons interacting via the long-range Coulomb force can form a Wigner crystal due to their mutual repulsion. This happens when the potential energy of the system dominates over its kinetic energy, i.e., at low temperatures for a classical system and at low densities for a quantum one. At $T=0$, the system is governed by quantum mechanics, and hence, the spatial density peaks associated with crystalline charge localization are sharpened for a lower average density. Conversely, in the classical limit of high temperatures, the crystalline spatial density peaks are suppressed (recovered) at a lower (higher) average density. In this paper, we study those two limits separately using an exact diagonalization of small one-dimensional (1D) systems containing few ($<10$) electrons and propose an approximate method to connect them into a unified effective phase diagram for Wigner few-electron crystallization. The result is a qualitative quantum-classical crossover phase diagram of an effective 1D Wigner crystal. We show that the spatial density peaks associated with the quasi-crystallization should be experimentally observable in a few-electron 1D system. We find that the effective crystalline structure slowly disappears with both the crossover average density and crossover temperature for crystallization decreasing with increasing particle number, consistent with the absence of any true long-range 1D order. In fact, one peculiar aspect of the effective finite-size nature of 1D Wigner crystallization we find is that even a short-range interaction would lead to a finite-size 1D crystal, except that the crystalline order vanishes much faster with increasing system size in the short-range interacting system compared with the long-range interacting one.
- arXiv:1902.02514 (replaced) [pdf, other]
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Title: Magnetoelectric Effects in Gyrotropic SuperconductorsComments: 5 pages, 1 figure, plus supplementary material. Comments are welcomeJournal-ref: Phys. Rev. Research 2, 012073 (2020)Subjects: Superconductivity (cond-mat.supr-con); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
The magnetoelectric effect (or Edelstein effect) in noncentrosymmetric superconductors states that a supercurrent can induce spin magnetization. This is an intriguing phenomenon which has potential applications in superconducting spintronic devices. However, the original Edelstein effect only applies to superconductors with polar point group symmetry. In recent years, many new noncentrosymmetric superconductors have been discovered, such as superconductors with chiral lattice symmetry and superconducting transition metal dichalcogenides with various lattice structures. In this Rapid Communication, we provide a general framework to describe the supercurrent-induced magnetization in these recently discovered superconductors with gyrotropic point groups.
- arXiv:1902.06649 (replaced) [pdf, other]
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Title: Phase transition in complex-time Loschmidt echo of short and long range spin chainComments: v2: several improvements made, final version; 37 pages, 8 figuresSubjects: Statistical Mechanics (cond-mat.stat-mech); Mathematical Physics (math-ph); Quantum Physics (quant-ph)
We explain and exploit the random matrix formulation of the Loschmidt echo for the XX spin chain, valid for multiple domain wall initial states and also for a XX spin chain generalized with additional interactions to more neighbours. For models with interactions decaying as $e^{-\alpha \left\vert l-j\right\vert }/\left\vert l-j\right\vert ^{p+1}$, with $p$ integer or natural number and $\alpha \geq 0$, we show that there are third order phase transitions in a double scaling limit of the complex-time Loschmidt echo amplitudes. For the long-range version of the chain, we use an exact result for Toeplitz determinants with a pure Fisher-Hartwig singularity, to obtain exactly the Loschmidt echo for complex times and discuss the associated Stokes phenomena. We also study the case of a finite chain for one of the generalized XX models.
- arXiv:1902.10516 (replaced) [pdf, ps, other]
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Title: No anomalous canonical commutators induced by Berry's phaseComments: 29 pages and 3 figures. Substantially expanded and a detailed account of the absence of no anomalous cononical commutators induced by Berry's phase is given. The title has also been changed accordingly. This version is to be published in Ann. of PhysSubjects: High Energy Physics - Theory (hep-th); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); High Energy Physics - Phenomenology (hep-ph)
The monopole-like singularity of Berry's adiabatic phase in momentum space and associated anomalous Poisson brackets have been recently discussed in various fields. With the help of the results of an exactly solvable version of Berry's model, we show that Berry's phase does not lead to the deformation of the principle of quantum mechanics in the sense of anomalous canonical commutators. If one should assume Berry's phase of genuine Dirac monopole-type, which is assumed to hold not only in the adiabatic limit but also in the non-adiabatic limit, the deformation of the principle of quantum mechanics could take place. But Berry's phase of the genuine Dirac monopole-type is not supported by the exactly solvable version of Berry's model nor by a generic model of Berry's phase. Besides, the monopole-like Berry's phase in momentum space has a magnetic charge $e_{M}=2\pi\hbar$, for which the possible anomalous term in the canonical commutator $[x_{k},x_{l}]=i\hbar\Omega_{kl}$ would become of the order $O(\hbar^{2})$.
- arXiv:1904.10867 (replaced) [pdf, other]
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Title: The Dyck bound in the concave 1-dimensional random assignment modelComments: 31 pages, 5 figuresJournal-ref: Journal of Physics A: Mathematical and Theoretical, 2020, 53.6: 064001Subjects: Disordered Systems and Neural Networks (cond-mat.dis-nn)
We consider models of assignment for random $N$ blue points and $N$ red points on an interval of length $2N$, in which the cost for connecting a blue point in $x$ to a red point in $y$ is the concave function $|x-y|^p$, for $0<p<1$. Contrarily to the convex case $p>1$, where the optimal matching is trivially determined, here the optimization is non-trivial. The purpose of this paper is to introduce a special configuration, that we call the \emph{Dyck matching}, and to study its statistical properties. We compute exactly the average cost, in the asymptotic limit of large $N$, together with the first subleading correction. The scaling is remarkable: it is of order $N$ for $p<\frac{1}{2}$, order $N \ln N$ for $p=\frac{1}{2}$, and $N^{\frac{1}{2}+p}$ for $p>\frac{1}{2}$, and it is universal for a wide class of models. We conjecture that the average cost of the Dyck matching has the same scaling in $N$ as the cost of the optimal matching, and we produce numerical data in support of this conjecture. We hope to produce a proof of this claim in future work.
- arXiv:1904.12005 (replaced) [pdf, other]
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Title: Classifying integrable spin-1/2 chains with nearest neighbour interactionsComments: Published versionSubjects: Mathematical Physics (math-ph); Statistical Mechanics (cond-mat.stat-mech); High Energy Physics - Theory (hep-th); Exactly Solvable and Integrable Systems (nlin.SI)
We classify all fundamental integrable spin chains with two-dimensional local Hilbert space which have regular R-matrices of difference form. This means that the R-matrix underlying the integrable structures is of the form R(u,v)=R(u-v) and reduces to the permutation operator at some particular point. We find a total of 14 independent solutions, 8 of which correspond to well-known eight or lower vertex models. The remaining 6 models appear to be new and some have peculiar properties such as not being diagonalizable or being nilpotent. Furthermore, for even R-matrices, we find a bijection between solutions of the Yang-Baxter equation and the graded Yang-Baxter equation which extends our results to the graded two-dimensional case.
- arXiv:1905.01702 (replaced) [pdf]
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Title: $Z_3$-vestigial nematic order due to superconducting fluctuations in the doped topological insulator Nb$_x$Bi$_2$Se$_3$ and Cu$_x$Bi$_2$Se$_3$Authors: Chang-woo Cho, Junying Shen, Jian Lyu, Omargeldi Atanov, Qianxue Chen, Seng Huat Lee, Yew San Hor, Dariusz Jakub Gawryluk, Ekaterina Pomjakushina, Marek Bartkowiak, Matthias Hecker, Jörg Schmalian, Rolf LortzSubjects: Superconductivity (cond-mat.supr-con)
A state of matter with a multi-component order parameter can give rise to vestigial order. In the vestigial phase, the primary order is only partially melted, leaving a remaining symmetry breaking behind, an effect driven by strong classical or quantum fluctuations. Vestigial states due to primary spin and charge-density-wave order have been discussed in the context of iron-based and cuprate materials. Here we present the observation of a partially melted superconductor in which pairing fluctuations condense at a separate phase transition and form a nematic state with broken Z3, i.e. three-state Potts-model symmetry. High-resolution thermal expansion, specific heat and magnetization measurements of the doped topological insulator NbxBi2Se3 reveal that this symmetry breaking occurs at Tnem=3.8 K above Tc=3.25 K, along with an onset of superconducting fluctuations. Thus, before Cooper pairs establish long-range coherence at Tc, they fluctuate in a way that breaks the rotational invariance at Tnem and induces a distortion of the crystalline lattice. Similar results are found for CuxBi2Se3.
- arXiv:1905.12377 (replaced) [pdf, other]
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Title: Enhancement in performance of quantum battery by ordered and disordered interactionsComments: 12 pages, 11 figures, close to published versionJournal-ref: Phys. Rev. A 101, 032115 (2020)Subjects: Quantum Physics (quant-ph); Disordered Systems and Neural Networks (cond-mat.dis-nn); Strongly Correlated Electrons (cond-mat.str-el)
Considering ground state of a quantum spin model as the initial state of the quantum battery, we show that both ordered and disordered interaction strengths play a crucial role to increase the extraction of power from it. In particular, we demonstrate that exchange interactions in the xy-plane and in the z-direction, leading to the XYZ spin chain, along with local charging field in the x-direction substantially enhance the efficiency of the battery compared to the model without interactions. Moreover, such an advantage in power obtained due to interactions is almost independent of the system size. We find that the behavior of the power, although measured during dynamics, can faithfully mimic the equilibrium quantum phase transitions present in the model. We observe that with the proper tuning of system parameters, initial state prepared at finite temperature can generate higher power in the battery than that obtained with zero-temperature. Finally, we report that defects or impurities, instead of reducing the performance, can create larger amount of quenched averaged power in the battery in comparison with the situation when the initial state is produced from the spin chain without disorder, thereby showing the disorder-induced order in dynamics.
- arXiv:1906.07670 (replaced) [pdf, other]
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Title: Intrinsic dimension estimation for locally undersampled dataJournal-ref: Scientific Reports volume 9, Article number: 17133 (2019)Subjects: Machine Learning (cs.LG); Disordered Systems and Neural Networks (cond-mat.dis-nn); Machine Learning (stat.ML)
High-dimensional data are ubiquitous in contemporary science and finding methods to compress them is one of the primary goals of machine learning. Given a dataset lying in a high-dimensional space (in principle hundreds to several thousands of dimensions), it is often useful to project it onto a lower-dimensional manifold, without loss of information. Identifying the minimal dimension of such manifold is a challenging problem known in the literature as intrinsic dimension estimation (IDE). Traditionally, most IDE algorithms are either based on multiscale principal component analysis (PCA) or on the notion of correlation dimension (and more in general on k-nearest-neighbors distances). These methods are affected, in different ways, by a severe curse of dimensionality. In particular, none of the existing algorithms can provide accurate ID estimates in the extreme locally undersampled regime, i.e. in the limit where the number of samples in any local patch of the manifold is less than (or of the same order of) the ID of the dataset. Here we introduce a new ID estimator that leverages on simple properties of the tangent space of a manifold to overcome these shortcomings. The method is based on the full correlation integral, going beyond the limit of small radius used for the estimation of the correlation dimension. Our estimator alleviates the extreme undersampling problem, intractable with other methods. Based on this insight, we explore a multiscale generalization of the algorithm. We show that it is capable of (i) identifying multiple dimensionalities in a dataset, and (ii) providing accurate estimates of the ID of extremely curved manifolds. In particular, we test the method on manifolds generated from global transformations of high-contrast images, relevant for invariant object recognition and considered a challenge for state-of-the-art ID estimators.
- arXiv:1907.00003 (replaced) [pdf, ps, other]
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Title: A charged finitely extensible dumbbell model: Explaining rheology of dilute polyelectrolyte solutionsComments: 36 pages, 8 figuresJournal-ref: Phys. Fluids 32, 063101 (2020)Subjects: Soft Condensed Matter (cond-mat.soft); Fluid Dynamics (physics.flu-dyn)
A robust non-Newtonian fluid model of dilute polyelectrolyte solutions is derived from kinetic theory arguments. Polyelectrolyte molecules are modeled as finitely elongated nonlinear elastic dumbbells, where effective charges (interacting through a simple Coulomb force) are added to the beads in order to model the repulsion between the charged sections of polyelectrolyte chains. It is shown that the relative strength of this repulsion is regulated by the electric-to-elastic energy ratio, $E$, which is one of the key parameters of the model. In particular, $E$ accounts for the intrinsic rigidity of polyelectrolyte molecules and can be used to explain the impact of solvent salinity on polyelectrolyte rheology. With two preaveraging approximations, the constitutive equations of the resulting fluid model are formulated in closed form. Material functions predicted by the model for steady shear flow, steady extensional flow, small-amplitude oscillatory shear flow, and start-up and cessation of steady shear flow are obtained and investigated using a combination of analytical and numerical methods. In particular, it is shown how these material functions depend on $E$. The two limiting cases of the model -- uncharged dumbbells ($E=0$) and rigid dumbbells ($E\to \infty$) -- are included in the analysis. It is found that despite its simplicity, the model predicts most of experimentally observed rheological features of polyelectrolyte solutions.
- arXiv:1907.11154 (replaced) [pdf, other]
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Title: Learning the dynamics of open quantum systems from their steady statesComments: 12 pages, 7 figuresJournal-ref: New J. Phys. 22, 032001 (2020)Subjects: Quantum Physics (quant-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Quantum Gases (cond-mat.quant-gas); Strongly Correlated Electrons (cond-mat.str-el)
Recent works have shown that generic local Hamiltonians can be efficiently inferred from local measurements performed on their eigenstates or thermal states. Realistic quantum systems are often affected by dissipation and decoherence due to coupling to an external environment. This raises the question whether the steady states of such open quantum systems contain sufficient information allowing for full and efficient reconstruction of the system's dynamics. We find that such a reconstruction is possible for generic local Markovian dynamics. We propose a recovery method that uses only local measurements; for systems with finite-range interactions, the method recovers the Lindbladian acting on each spatial domain using only observables within that domain. We numerically study the accuracy of the reconstruction as a function of the number of measurements, type of open-system dynamics and system size. Interestingly, we show that couplings to external environments can in fact facilitate the reconstruction of Hamiltonians composed of commuting terms.
- arXiv:1908.02248 (replaced) [pdf, other]
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Title: Provable bounds for the Korteweg-de Vries reduction in multi-component Nonlinear Schrodinger EquationComments: 21 pages, 2 FiguresJournal-ref: J. Phys. A: Math. Theor. 53 (2020) 135206Subjects: Mathematical Physics (math-ph); Quantum Gases (cond-mat.quant-gas); Exactly Solvable and Integrable Systems (nlin.SI); Optics (physics.optics)
We study the dynamics of multi-component Bose gas described by the Vector Nonlinear Schr\"{o}dinger Equation (VNLS), aka the Vector Gross--Pitaevskii Equation (VGPE) . Through a Madelung transformation, the VNLS can be reduced to coupled hydrodynamic equations in terms of multiple density and velocity fields. Using a multi-scaling and a perturbation method along with the Fredholm alternative, we reduce the problem to a Korteweg de-Vries (KdV) system. This is of great importance to study more transparently, the obscure features hidden in VNLS. This ensures that hydrodynamic effects such as dispersion and nonlinearity are captured at an equal footing. Importantly, before studying the KdV connection, we provide a rigorous analysis of the linear problem. We write down a set of theorems along with proofs and associated corollaries that shine light on the conditions of existence and nature of eigenvalues and eigenvectors of the linear problem. This rigorous analysis is paramount for understanding the nonlinear problem and the KdV connection. We provide strong evidence of agreement between VNLS systems and KdV equations by using soliton solutions as a platform for comparison. Our results are expected to be relevant not only for cold atomic gases, but also for nonlinear optics and other branches where VNLS equations play a defining role.
- arXiv:1908.09268 (replaced) [pdf, ps, other]
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Title: Effects of random fields on the reversal of magnetisation of Ising ferromagnetComments: 12 pages Latex and 19 captioned figures, To appear in Physica A (2020)Journal-ref: Physica A 551 (2020) 124583Subjects: Statistical Mechanics (cond-mat.stat-mech)
We have studied the reversal time of the magnetisation in two dimensional Ising ferromagnet in the presence of externally applied uniform magnetic field using Monte Carlo simulation based on Metropolis single spin flip algorithm. Then we have investigated the change in reversal time due to the presence of quenched random field in addition to the uniform magnetic field. We report the results of statistical distribution of reversal times in the presence of three different types of the distributions (namely, uniform, bimodal and normal) of random fields and compared the results with those obtained for uniform field only. We have observed that the reversal time decreases due to the presence of any kind (of distribution) of the random fields. The metastable volume fraction is observed to follow the Avrami's law. Dependence of reversal times on temperature and different widths of the distributions of random fields are also reported. We have also checked whether the system obeyed Becker-Doring theory of classical nucleation in presence of additional random field and tried to investigate the range of the width of the distribution of random field. For larger width of the distribution of random field, the system fails to show the reversal via the nucleation of a single droplet (for small values of uniform field only). The possible reason is analysed.
- arXiv:1909.00396 (replaced) [pdf]
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Title: Phonon Gravity, Non-equilibrium QFT, and the Tolman Thermal Equivalence PrincipleAuthors: Alyx JourjineComments: 16 pages. Extended edition. Some minor typos fixed. The Quantum Steady State definition augmented. To appear in the Journal of Theoretical and Mathematical Physics, RussiaSubjects: High Energy Physics - Theory (hep-th); Statistical Mechanics (cond-mat.stat-mech); Strongly Correlated Electrons (cond-mat.str-el); General Relativity and Quantum Cosmology (gr-qc)
We describe an extension of the Keldysh method for fermions from constant temperature to steady state case with spatially varying temperature field.This is done with the use on the imaginary section of the Keldysh path of a thermal Hamiltonian obtained from the zero temperature relativistic Hamiltonian by coupling its density multiplicatively to the temperature field. We show that the two Hamiltonians commute, provided appropriate boundary conditions are imposed. A microscopical equation on the temperature field and the corresponding microscopical Fourier law of heat transfer are derived for the relativistic and the non-relativistic cases. We discuss application of the proposed method to the thermoelectric effect and point out a remarkable correspondence between the non-equilibrium thermal Hamiltonian and the zero temperature fermionic Hamiltonian in general relativity for the metric obtained from the Minkowski metric by rescaling time with the inverse temperature.Our results suggest the existence of the correspondence principle between gravitating equilibrium and non-gravitating non-equilibrium quantum field theories, which we call the Tolman thermal equivalence principle in honor of his pioneering work.
- arXiv:1909.06095 (replaced) [pdf, ps, other]
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Title: Collective dynamics of phase-repulsive oscillators solves graph coloring problemJournal-ref: Chaos 30, 033128 (2020)Subjects: Chaotic Dynamics (nlin.CD); Statistical Mechanics (cond-mat.stat-mech); Combinatorics (math.CO); Optimization and Control (math.OC)
We show how to couple phase-oscillators on a graph so that collective dynamics "searches" for the coloring of that graph as it relaxes toward the dynamical equilibrium. This translates a combinatorial optimization problem (graph coloring) into a functional optimization problem (finding and evaluating the global minimum of dynamical non-equilibrium potential, done by the natural system's evolution). Using a sample of graphs, we show that our method can serve as a viable alternative to the traditional combinatorial algorithms. Moreover, we show that, with the same computational cost, our method efficiently solves the harder problem of improper coloring of weighed graphs.
- arXiv:1909.06438 (replaced) [pdf, other]
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Title: Influence of nuclear spin polarization on spin echo signal of NV center qubitComments: Presentation thoroughly improved, changed titleJournal-ref: Phys. Rev. B 101, 155412 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Quantum Physics (quant-ph)
We consider the spin echo dynamics of a nitrogen-vacancy center qubit based the $S\!= \! 1$ ground state spin manifold, caused by a dynamically polarized nuclear environment. We show that the echo signal acquires then a nontrivially time-dependent phase shift. This effect should be observable for polarization $\approx \! 0.5$ of nuclei within $\sim \! 1$ nm from the qubit, and for the NV center initialized in a superposition of $m\! = \! 0$ and either $m\! =\! 1$ or $m\! =\! -1$ states. This phase shift is much smaller when the NV center is prepared in a superposition of $m\! = \! 1$ and $m\! =\! -1$ states, i.e. when the qubit couples to the spin environment in a way analogous to that of spin-$1/2$. For nuclear environment devoid of spins strongly coupled to the qubit, the phase shift is well described within Gaussian approximation, which provides an explanation for the dependence of the shift magnitude on the choice of states on which the qubit is based, and makes it clear that its presence is related to the linear response of the environment perturbed by an evolving qubit. Consequently, its observation signifies the presence environment-mediated self-interaction of the qubit, and hence, it invalidates the notion that the nuclear environment acts as a source of external noise driving the qubit. We also show how a careful comparison of the echo signal from qubits based on $m\! = \! 0,1$ and $m\! =\! \pm 1$ manifolds, can distinguish between effectively Gaussian and non-Gaussian environment.
- arXiv:1910.00285 (replaced) [pdf, other]
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Title: Blind calibration for compressed sensing: State evolution and an online algorithmSubjects: Statistical Mechanics (cond-mat.stat-mech); Disordered Systems and Neural Networks (cond-mat.dis-nn); Information Theory (cs.IT)
Compressed sensing, allows to acquire compressible signals with a small number of measurements. In applications, a hardware implementation often requires a calibration as the sensing process is not perfectly known. Blind calibration, that is performing at the same time calibration and compressed sensing is thus particularly appealing. A potential approach was suggested by Sch\"ulke and collaborators in Sch\"ulke et al. 2013 and 2015, using approximate message passing (AMP) for blind calibration (cal-AMP). Here, the algorithm is extended from the already proposed offline case to the online case, where the calibration is refined step by step as new measured samples are received. Furthermore, we show that the performance of both the offline and the online algorithms can be theoretically studied via the State Evolution (SE) formalism. Through numerical simulations, the efficiency of cal-AMP and the consistency of the theoretical predictions are confirmed.
- arXiv:1910.00476 (replaced) [pdf, other]
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Title: Inferring entropy production from short experimentsComments: Main text- 4 pages and 7 figures. Supplementary material- 5 pages, 3 Figures Version published onlineJournal-ref: Phys. Rev. Lett. 124, 120603 (2020)Subjects: Statistical Mechanics (cond-mat.stat-mech)
We provide a strategy for an exact inference of the average as well as the fluctuations of the entropy production in non-equilibrium systems in the steady state, from the measurements of arbitrary current fluctuations. Our results are built upon the finite time generalization of the thermodynamic uncertainty relation, and require only very short time series data from experiments. We illustrate our results with exact and numerical solutions for two colloidal heat engines.
- arXiv:1910.02518 (replaced) [pdf, other]
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Title: Self-similar dynamics of order parameter fluctuations in pump-probe experimentsJournal-ref: Phys. Rev. B 101, 174306 (2020)Subjects: Other Condensed Matter (cond-mat.other)
Upon excitation by a laser pulse, broken-symmetry phases of a wide variety of solids demonstrate similar order parameter dynamics characterized by a dramatic slowing down of relaxation for stronger pump fluences. Motivated by this recurrent phenomenology, we develop a simple non-perturbative effective model of dynamics of collective bosonic excitations in pump-probe experiments. We find that as the system recovers after photoexcitation, it shows universal prethermalized dynamics manifesting a power-law, as opposed to exponential, relaxation, explaining the slowing down of the recovery process. For strong quenches, long-wavelength over-populated transverse modes dominate the long-time dynamics; their distribution function exhibits universal scaling in time and space, whose universal exponents can be computed analytically. Our model offers a unifying description of order parameter fluctuations in a regime far from equilibrium, and our predictions can be tested with available time-resolved techniques.
- arXiv:1910.07369 (replaced) [pdf, other]
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Title: FQHE and $tt^{*}$ geometryAuthors: Riccardo BergaminComments: Doctoral thesis, SISSA, Trieste, Italy (2019)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); High Energy Physics - Theory (hep-th); Mathematical Physics (math-ph)
Cumrun Vafa proposed a new unifying model for the principal series of FQHE which predicts non-Abelian statistics of the quasi-holes. The many-body Hamiltonian supporting these topological phases of matter is invariant under four supersymmetries. In the thesis we study the geometrical properties of this Landau-Ginzburg theory. The emerging picture is in agreement with the Vafa's predictions. The $4$-SQM Vafa Hamiltonian is shown to capture the topological order of FQHE and the $tt^{*}$ monodromy representation of the braid group factors through a Temperley-Lieb/Hecke algebra with $q = \pm \exp(\pi i/\nu)$. In particular, the quasi-holes have the same non-Abelian braiding properties of the degenerate field $\phi_{1,2}$ in Virasoro minimal models. Part of the thesis is dedicated to minor results about the geometrical properties of the Vafa model for the case of a single electron. In particular, we study a special class of models which reveal a beautiful connection between the physics of quantum Hall effect and the geometry of modular curves. Despite it is not relevant for phenomenological purposes, this class of theories has remarkable properties which enlarge further the rich mathematical structure of FQHE.
- arXiv:1910.07530 (replaced) [pdf, other]
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Title: $T$-linear resistivity in models with local self-energySubjects: Strongly Correlated Electrons (cond-mat.str-el)
A theoretical understanding of the enigmatic linear-in-temperature ($T$) resistivity, ubiquitous in strongly correlated metallic systems, has been a long sought-after goal. Furthermore, the slope of this robust $T$-linear resistivity is also observed to stay constant through crossovers between different temperature regimes: a phenomenon we dub "slope invariance". Recently, several solvable models with $T$-linear resistivity have been proposed, putting us in an opportune moment to compare their inner workings in various explicit calculations. We consider two strongly correlated models with local self-energies that demonstrate $T$-linearity: a lattice of coupled Sachdev-Ye-Kitaev (SYK) models and the Hubbard model in single-site dynamical mean-field theory (DMFT). We find that the two models achieve $T$-linearity through distinct mechanisms at intermediate temperatures. However, we also find that these mechanisms converge to an identical form at high temperatures. Surprisingly, both models exhibit "slope invariance" across the two temperature regimes. We thus not only reveal some of the diversity in the theoretical inner workings that can lead to $T$-linear resistivity, but we also establish that different mechanisms can result in "slope invarance".
- arXiv:1910.12189 (replaced) [pdf, ps, other]
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Title: Revisiting weak measurement in light of thermodynamicsComments: 8 pagesSubjects: Statistical Mechanics (cond-mat.stat-mech); Quantum Gases (cond-mat.quant-gas); Quantum Physics (quant-ph)
We investigate a weak measurement described by a von Neumann type interaction $\hat{A}\otimes \hat{p}^2$, where $\hat{A}$ is a system observable and $\hat{p}^2$ is a measurement pointer observable. We consider the weak measurement in terms of thermodynamics by adopting a mixed Gaussian state as a quantum state of the measurement pointer. We show that Maxwell's demon appears as a measure who carries out post-selections. It is found that, even if the demon only knows the weak value, a difference in the von Neumann entropy between the initial and final system can be the QC mutual information contents, which is the maximum amount of obtainable information by a measurement. Besides, our study indicates that a temperature of the system described by this interaction is amplified by weak value amplification. In addition, we show that this demon can be realized in an atomic system.
- arXiv:1910.13266 (replaced) [pdf, other]
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Title: Steady one-dimensional domain wall motion in biaxial ferromagnets: mapping of the Landau-Lifshitz equation to the sine-Gordon equationJournal-ref: Phys. Rev. B 101, 094416 (2020)Subjects: Materials Science (cond-mat.mtrl-sci); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Motivated by the difference between the dynamics of magnetization textures in ferromagnets and antiferromagnets, the Landau-Lifshitz equation of motion is explored. A typical one-dimensional domain wall in a bulk ferromagnet with biaxial magnetic anisotropy is considered. In the framework of Walker-type of solutions of steady-state ferromagnetic domain wall motion, the reduction of the non-linear Landau-Lifshitz equation to a Lorentz-invariant sine-Gordon equation typical for antiferromagnets is formally possible for velocities lower than a critical velocity of the topological soliton. The velocity dependence of the domain wall energy and the domain wall width are expressed in the relativistic-like form in the limit of large ratio of the easy-plane/easy-axis anisotropy constants. It is shown that the mapping of the Landau-Lifshitz equation of motion to the sine-Gordon equation can be performed only by going beyond the steady-motion Walker-type of solutions.
- arXiv:1910.14433 (replaced) [pdf, other]
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Title: A binary mixture of Bose-Einstein-condensates in a double-well potential: Berry phase and two-mode entanglementAuthors: Mehmet GünayComments: 7 pages, 3 figuresJournal-ref: Phys. Rev. A 101, 043608 (2020)Subjects: Quantum Gases (cond-mat.quant-gas); Atomic and Molecular Clusters (physics.atm-clus); Atomic Physics (physics.atom-ph); Optics (physics.optics); Quantum Physics (quant-ph)
A binary mixtures of Bose-Einstein condensate structures exhibit an incredible richness in terms of holding different kinds of phases. Depending on the ratio of the inter- and intra-atomic interactions, the transition from mixed to separated phase, which is also known as the miscibility-immiscibility transition, has been reported in different setups and by different groups. Here, we describe such type of quantum phase transition in an effective Hamiltonian approach, by applying Holstein-Primakoff transformation in the limit of large number of particles. We demonstrate that non-trivial geometric phase near the critical coupling is present, which confirms the connection between Berry phase and quantum phase transition. We also show that, by using the spin form of Hillery & Zubairy criterion, a two mode entanglement accompanies this transition in the limit of large, but not infinite number of particles.
- arXiv:1910.14470 (replaced) [pdf, ps, other]
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Title: Coherent spin pumping in a strongly coupled magnon-magnon hybrid systemAuthors: Yi Li, Wei Cao, Vivek P. Amin, Zhizhi Zhang, Jonathan Gibbons, Joseph Sklenar, John Pearson, Paul M. Haney, Mark D. Stiles, William E. Bailey, Valentine Novosad, Axel Hoffmann, Wei ZhangJournal-ref: Phys. Rev. Lett. 124, 117202 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We experimentally identify coherent spin pumping in the magnon-magnon hybrid modes of permalloy/yttrium iron garnet (Py/YIG) bilayers. Using broadband ferromagnetic resonance, an "avoided crossing" is observed between the uniform mode of Py and the spin wave mode of YIG due to the fieldlike interfacial exchange coupling. We also identify additional linewidth suppression and enhancement for the in-phase and out-of-phase hybrid modes, respectively, \textcolor{black}{which can be interpreted as concerted dampinglike torque from spin pumping}. Our analysis predicts inverse proportionality of both fieldlike and dampinglike torques to the square root of the Py thickness, which quantitatively agrees with experiments.
- arXiv:1910.14621 (replaced) [pdf, other]
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Title: Ferromagnetic fluctuations in the Rashba-Hubbard modelComments: 7 pages, 5 figuresJournal-ref: Phys. Rev. B 101, 174420 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el); Superconductivity (cond-mat.supr-con)
We study the occurrence and the origin of ferromagnetic fluctuations in the longitudinal spin susceptibility of the $t$-$t'$-Rashba-Hubbard model on the square lattice. The combined effect of the second-neighbor hopping $t'$ and the spin-orbit coupling leads to ferromagnetic fluctuations in a broad filling region. The spin-orbit coupling splits the energy bands, leading to two van Hove fillings, where the sheets of the Fermi surface change their topology. Between these two van Hove fillings the model shows ferromagnetic fluctuations. We find that these ferromagnetic fluctuations originate from interband contributions to the spin susceptibility. These interband contributions only arise if there is one holelike and one electronlike Fermi surface, which is the case for fillings in between the two van Hove fillings. We discuss implications for experimental systems and propose a test on how to identify these types of ferromagnetic fluctuations in experiments.
- arXiv:1911.00998 (replaced) [pdf, other]
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Title: Thermal Efficiency of Quantum Memory CompressionComments: 7 pages, 3 figures; Supplementary material: 8 pages, 1 figure; this http URLSubjects: Quantum Physics (quant-ph); Statistical Mechanics (cond-mat.stat-mech); Information Theory (cs.IT)
Quantum coherence allows for reduced-memory simulators of classical processes. Using recent results in single-shot quantum thermodynamics, we derive a minimal work cost rate for quantum simulators that is quasistatically attainable in the limit of asymptotically-infinite parallel simulation. Comparing this cost with the classical regime reveals that quantizing classical simulators not only results in memory compression but also in reduced dissipation. We explore this advantage across a suite of representative examples.
- arXiv:1911.01439 (replaced) [pdf, other]
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Title: New integrable 1D models of superconductivityComments: typos and referencesSubjects: Mathematical Physics (math-ph); Statistical Mechanics (cond-mat.stat-mech); High Energy Physics - Theory (hep-th); Exactly Solvable and Integrable Systems (nlin.SI)
In this paper we find new integrable one-dimensional lattice models of electrons. We classify all such nearest-neighbour integrable models with su(2)xsu(2) symmetry following the procedure first introduced in arXiv:1904.12005. We find 12 R-matrices of difference form, some of which can be related to known models such as the XXX spin chain and the free Hubbard model, and some are new models. In addition, integrable generalizations of the Hubbard model are found by keeping the kinetic term of the Hamiltonian and adding all terms which preserve fermion number. We find that most of the new models can not be diagonalized using the standard nested Bethe Ansatz.
- arXiv:1911.03177 (replaced) [pdf, other]
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Title: Core-level x-ray photoemission and Raman spectroscopy studies on electronic structures in Mott-Hubbard type nickelate oxide NdNiO$_2$Authors: Ying Fu, Le Wang, Hu Cheng, Shenghai Pei, Xuefeng Zhou, Jian Chen, Shaoheng Wang, Ran Zhao, Wenrui Jiang, Cai Liu, Mingyuan Huang, XinWei Wang, Yusheng Zhao, Dapeng Yu, Fei Ye, Shanmin Wang, Jia-Wei MeiComments: 7 pages, 5 figuresSubjects: Superconductivity (cond-mat.supr-con); Strongly Correlated Electrons (cond-mat.str-el)
We perform core-level X-ray photoemission spectroscopy (XPS) and electronic Raman scattering studies of electronic structures and spin fluctuations in the bulk samples of the nickelate oxide NdNiO$_2$. According to Nd $3d$ and O $1s$ XPS spectra, we conclude that NdNiO$_2$ has a large transfer energy. From the analysis of the main line of the Ni $2p_{3/2}$ XPS, we confirm the NiO$_2$ planes in NdNiO$_2$ are of Mott-Hubbard type in the Zaanen-Sawatzky-Allen scheme. The two-magnon peak in the Raman scattering provides direct evidence for the strong spin-fluctuation in NdNiO$_2$. The peak position determines the antiferromagnetic exchange $J=25$~meV. Our experimental results agree well with our previous theoretical results.
- arXiv:1911.03643 (replaced) [pdf, ps, other]
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Title: Periodically-driven facilitated high-efficiency dissipative entanglement with Rydberg atomsComments: 9 pages, 7 figures, accepted by Physical Review AJournal-ref: Phys. Rev. A 101, 042328 (2020)Subjects: Atomic Physics (physics.atom-ph); Quantum Gases (cond-mat.quant-gas); Quantum Physics (quant-ph)
A time-dependent periodical field can be utilized to efficiently modify the Rabi coupling of system, exhibiting nontrivial dynamics. We propose a scheme to show that this feature can be applied for speeding up the formation of dissipative steady entanglement based on Rydberg anti-blockade mechanism in a simplified configuration, fundamentally stemming from a frequency match between the external-field modulation frequency and the systematic characteristic frequency. In the presence of an optimal modulation frequency that is exactly equal to the central frequency of driving field, it enables a sufficient residence time of the two-excitation Rydberg state for an irreversible spontaneous decay onto the target state, leading to an accelerated high-fidelity steady entanglement ~0.98, with a shorter formation time <400\mu s. We show that, a global maximal fidelity benefits from a consistence of microwave-field coupling and spontaneous decay strengths, by which the scheme promises a robust insensitivity to the initial population distributions. This simple approach to facilitate the generation of dissipative entangled two-qubit states by using periodic drivings may guide a new experimental direction in Rydberg quantum technology and quantum information.
- arXiv:1911.05057 (replaced) [pdf, other]
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Title: Interaction-induced lattices for bound states: Designing flat bands, quantized pumps and higher-order topological insulators for doublonsComments: 10 pages,7 figuresJournal-ref: Phys. Rev. Research 2, 013348 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Quantum Gases (cond-mat.quant-gas)
Bound states of two interacting particles moving on a lattice can exhibit remarkable features that are not captured by the underlying single-particle picture. Inspired by this phenomenon, we introduce a novel framework by which genuine interaction-induced geometric and topological effects can be realized in quantum-engineered systems. Our approach builds on the design of effective lattices for the center-of-mass motion of two-body bound states (\emph{doublons}), which can be created through long-range interactions. This general scenario is illustrated on several examples, where flat-band localization, topological pumps and higher-order topological corner modes emerge from genuine interaction effects. Our results pave the way for the exploration of interaction-induced topological effects in a variety of platforms, ranging from ultracold gases to interacting photonic devices.
- arXiv:1911.07138 (replaced) [pdf, other]
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Title: Theory of two-dimensional nonlinear spectroscopy for the Kitaev spin liquidComments: 5 pages, 2 figures + Supplemental Materials(6 pages, 2 figures)Journal-ref: Phys. Rev. Lett. 124, 117205 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Unambiguous identification of fractionalized excitations in quantum spin liquids has been a long-standing issue in correlated topological phases. Conventional spectroscopic probes, such as the dynamical spin structure factor, can only detect composites of fractionalized excitations, leading to a broad continuum in energy. Lacking a clear signature in conventional probes has been the biggest obstacle in the field. In this work, we theoretically investigate what kinds of distinctive signatures of fractionalized excitations can be probed in two-dimensional nonlinear spectroscopy by considering the exactly solvable Kitaev spin liquids. We demonstrate the existence of a number of salient features of the Majorana fermions and fluxes in two-dimensional nonlinear spectroscopy, which provide crucial information about such excitations.
- arXiv:1911.08982 (replaced) [pdf, other]
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Title: Parabolic Hall Effect due to Co-Propagating Surface ModesAuthors: Maxim BreitkreizComments: 5 pages + 4 pages Supplemental Material, 3 figuresJournal-ref: Phys. Rev. Research 2, 012071 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Real-space separations of counter-moving states to opposite surfaces or edges are associated with different types of Hall effects, such as the quantum-, spin-, or the anomalous Hall effect. Some systems provide the possibility to separate a fraction of countermovers in a completely different fashion: Surface states propagating all in the same direction, balanced by counter-moving bulk states, realized, e.g., in Weyl metals with intrinsically or extrinsically broken inversion and time-reversal symmetries. In this work we show that these co-propagating surface modes are associated with a novel Hall effect --- a parabolic potential profile in the direction perpendicular to and in its magnitude linear in the applied field. While in 2D systems the parabolic potential profile is measurable directly, in 3D the resulting voltage between bulk and surface is measurable in the geometry of a hollow cylinder. Moreover, the parabolic Hall effect leads to characteristic signatures in the longitudinal conductivity.
- arXiv:1911.09203 (replaced) [pdf, other]
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Title: $\mathbb{Z}_{n}$ superconductivity of composite bosons and the $7/3$ fractional quantum Hall effectComments: 17 pages, 7 figures, published versionJournal-ref: Phys. Rev. Research 2, 013349 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); High Energy Physics - Theory (hep-th)
The topological $p$-wave pairing of composite fermions, believed to be responsible for the 5/2 fractional quantum Hall effect (FQHE), has generated much exciting physics. Motivated by the parton theory of the FQHE, we consider the possibility of a new kind of emergent "superconductivity" in the 1/3 FQHE, which involves condensation of clusters of $n$ composite bosons. From a microscopic perspective, the state is described by the $n\bar{n}111$ parton wave function ${\cal P}_{\rm LLL} \Phi_n\Phi_n^*\Phi_1^3$, where $\Phi_n$ is the wave function of the integer quantum Hall state with $n$ filled Landau levels and ${\cal P}_{\rm LLL}$ is the lowest-Landau-level projection operator. It represents a $\mathbb{Z}_{n}$ superconductor of composite bosons, because the factor $\Phi_1^3\sim \prod_{j<k}(z_j-z_k)^3$, where $z_j=x_j-iy_j$ is the coordinate of the $j$th electron, binds three vortices to electrons to convert them into composite bosons, which then condense into the $\mathbb{Z}_{n}$ superconducting state $|\Phi_n|^2$. From a field theoretical perspective, this state can be understood by starting with the usual Laughlin theory and gauging a $\mathbb{Z}_n$ subgroup of the $U(1)$ charge conservation symmetry. We find from detailed quantitative calculations that the $2\bar{2}111$ and $3\bar{3}111$ states are at least as plausible as the Laughlin wave function for the exact Coulomb ground state at filling $\nu=7/3$, suggesting that this physics is possibly relevant for the 7/3 FQHE. The $\mathbb{Z}_{n}$ order leads to several observable consequences, including quasiparticles with fractionally quantized charges of magnitude $e/(3n)$ and the existence of multiple neutral collective modes. It is interesting that the FQHE may be a promising venue for the realization of exotic $\mathbb{Z}_{n}$ superconductivity.
- arXiv:1911.11443 (replaced) [pdf, other]
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Title: Macroscopic Matter Wave Quantum TunnellingComments: 22 Pages, 6 figuresJournal-ref: Commun Phys 3, 101 (2020)Subjects: Quantum Gases (cond-mat.quant-gas)
Quantum tunneling is a phenomenon of non-equilibrium quantum dynamics and its detailed process is largely unexplored. We report the experimental observation of macroscopic quantum tunneling of Bose-Einstein Condensate in a hybrid trap. By exerting a non-adiabatic kick to excite a collective rotation mode of the trapped condensate, a periodic pulse train, which remains as condensate, is then out-coupled by quantum tunneling. This non-equilibrium dynamics is analogue to tunneling ionization. The imaged tunneling process shows the splitting of matter-wave packet by the potential barrier. The controversial "tunneling time" question is found inadequate, from the point of view of wave propagation. The realized matter-wave pulse train can also be a passive pulsed atom laser for atom interferometer applications.
- arXiv:1912.00970 (replaced) [pdf, other]
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Title: $\sqrt{2}$$\times$$\sqrt{2}R45^\circ$ surface reconstruction and electronic structure of BaSnO$_3$ filmAuthors: Shoresh Soltani, Sungyun Hong, Bongju Kim, Donghan Kim, Jong Keun Jun, Byungmin Sohn, Tae Won Noh, Kookrin Char, Changyoung KimComments: 7 pages, 4 figures, JournalJournal-ref: Phys. Rev. Materials 4, 055003 (2020)Subjects: Materials Science (cond-mat.mtrl-sci)
We studied surface and electronic structures of barium stannate (BaSnO$_3$) thin-film by low energy electron diffraction (LEED), and angle-resolved photoemission spectroscopy (ARPES) techniques. BaSnO$_3$/Ba$_{0.96}$La$_{0.04}$SnO$_3$/SrTiO$_3$ (10 nm/100 nm/0.5 mm) samples were grown using pulsed-laser deposition (PLD) method and were \emph{ex-situ} transferred from PLD chamber to ultra-high vacuum (UHV) chambers for annealing, LEED and ARPES studies. UHV annealing starting from 300$^{\circ}$C up to 550$^{\circ}$C, followed by LEED and ARPES measurements show 1$\times$1 surfaces with non-dispersive energy-momentum bands. The 1$\times$1 surface reconstructs into a $\sqrt{2}$$\times$$\sqrt{2}R45^\circ$ one at the annealing temperature of 700$^{\circ}$C where the ARPES data shows clear dispersive bands with valence band maximum located around 3.3 eV below Fermi level. While the $\sqrt{2}$$\times$$\sqrt{2}R45^\circ$ surface reconstruction is stable under further UHV annealing, it is reversed to 1$\times$1 surface by annealing the sample in 400 mTorr oxygen at 600$^{\circ}$C. Another UHV annealing at 600$^{\circ}$C followed by LEED and ARPES measurements, suggests that LEED $\sqrt{2}$$\times$$\sqrt{2}R45^\circ$ surface reconstruction and ARPES dispersive bands are reproduced. Our results provide a better picture of electronic structure of BaSnO$_3$ surface and are suggestive of role of oxygen vacancies in the reversible $\sqrt{2}$$\times$$\sqrt{2}R45^\circ$ surface reconstruction.
- arXiv:1912.02564 (replaced) [pdf, other]
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Title: Melting of excitonic dispersion in LaCoO$_3$: theory and experimentAuthors: Atsushi Hariki, Ru-Pan Wang, Andrii Sotnikov, Keisuke Tomiyasu, Davide Betto, Nicholas B. Brookes, Yohei Uemura, Mahnaz Ghiasi, Frank M. F. de Groot, Jan KunešSubjects: Strongly Correlated Electrons (cond-mat.str-el); Materials Science (cond-mat.mtrl-sci)
We present Co $L_3$-edge resonant inelastic x-ray scattering (RIXS) of bulk LaCoO$_3$ across the thermally-induced spin-state crossover around 100K. Owing to a high energy resolution of 25meV, we observe unambiguously the dispersion of the intermediate-spin (IS) excitations in the low temperature regime. Approaching the intermediate temperature regime, the IS excitations are damped and the bandwidth reduced. The observed behavior can be well described by a model of mobile IS excitons with strong attractive interaction, which we solve using dynamical mean-field theory for hard-core bosons. Our results provide a detailed mechanism of how HS and IS excitations interact to establish the physical properties of cobaltite perovskites.
- arXiv:1912.03292 (replaced) [pdf, ps, other]
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Title: A large deviation perspective on ratio observables in reset processes: robustness of rate functionsComments: 17 pages, 15 figuresJournal-ref: J Stat Phys 179 (2020)Subjects: Statistical Mechanics (cond-mat.stat-mech)
We study large deviations of a ratio observable in discrete-time reset processes. The ratio takes the form of a current divided by the number of reset steps and as such it is not extensive in time. A large deviation rate function can be derived for this observable via contraction from the joint probability density function of current and number of reset steps. The ratio rate function is differentiable and we argue that its qualitative shape is 'robust', i.e. it is generic for reset processes regardless of whether they have short- or long-range correlations. We discuss similarities and differences with the rate function of the efficiency in stochastic thermodynamics.
- arXiv:1912.06440 (replaced) [pdf, other]
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Title: Thermal conductivity of Bi$_2$Se$_3$ from bulk to thin films: theory and experimentAuthors: Lorenzo Paulatto, Danièle Fournier, Massimiliano Marangolo, Mahmoud Eddrief, Paola Atkinson, Matteo CalandraSubjects: Materials Science (cond-mat.mtrl-sci)
We calculate the lattice-driven in-plane $(\kappa_{\parallel})$ and out-of-plane $(\kappa_{\perp})$ thermal conductivities of Bi$_2$Se$_3$ bulk, and of films of different thicknesses, using the Boltzmann equation with phonon scattering times obtained from anharmonic third order density functional perturbation theory.
We compare our results for the lattice component of the thermal conductivity with published data for $\kappa_{\parallel}$ on bulk samples and with our room-temperature thermoreflectance measurements of $\kappa_{\perp}$ on films of thickness (L) ranging from 18~nm to 191~nm, where the lattice component has been extracted via the Wiedemann-Franz law. Ab-initio theoretical calculations on bulk samples, including an effective model to account for finite sample thickness and defect scattering, compare favorably both for the bulk case (from literature) and thin films (new measurements). In the low-T limit the theoretical in-plane lattice thermal conductivity of bulk Bi$_2$Se$_3$ agrees with previous measurements by assuming the occurrence of intercalated Bi$_2$ layer defects. The measured thermal conductivity monotonically decreases by reducing $L$, its value is $\kappa_{\perp}\approx 0.39\pm 0.08$~W/m$\cdot$K for $L=18$ nm and $\kappa_{\perp}=0.68\pm0.14$~W/m$\cdot$K for $L=191$ nm. We show that the decrease of room-temperature $\kappa_{\perp}$ in Bi$_2$Se$_3$ thin films as a function of sample thickness can be explained by the incoherent scattering of out-of-plane momentum phonons with the film surface. Our work outlines the crucial role of sample thinning in reducing the out-of-plane thermal conductivity. - arXiv:1912.08121 (replaced) [pdf]
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Title: Modeling Escape from a One-Dimensional Potential Well at Zero or Very Low TemperaturesAuthors: Chungho Cheng, Gaetano Salina, Niels Grønbech-Jensen, James A. Blackburn, Massimiliano Lucci, Matteo CirilloComments: 25 pages and 13 FiguresJournal-ref: J. Appl. Phys. 127, 143901 (2020);Subjects: Statistical Mechanics (cond-mat.stat-mech); Chaotic Dynamics (nlin.CD)
The process of activation out a one-dimensional potential is investigated systematically in zero and nonzero temperature conditions. The features of the potential are traced through statistical escape out of its wells whose depths are tuned in time by a forcing term. The process is carried out on the damped pendulum system imposing specific initial conditions on the potential variable. While for relatively high values of the dissipation the statistical properties follow a behavior that can be derived from the standard Kramers model, decreasing the dissipation we observe responses/deviations which have regular dependencies on initial conditions, temperature, and loss parameter itself. It is shown that failures of the thermal activation model are originated at low temperatures, and very low dissipation, by the initial conditions and intrinsic, namely T=0, characteristic oscillations of the potential-generated dynamical equation.
- arXiv:1912.09292 (replaced) [pdf, other]
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Title: How capillarity affects the propagation of elastic waves in soft gelsJournal-ref: Phys. Rev. E 101, 032609 (2020)Subjects: Soft Condensed Matter (cond-mat.soft)
Elastic waves propagating at the interface of soft solids can be altered by the presence of external forces such as capillarity or gravity. We measure the dispersion relation of waves at the free surface of agarose gels with great accuracy, revealing the existence of multiple modes as well as an apparent dispersion. We disentangle the role of capillarity and elasticity by considering the 3D nature of mechanical waves, achieving quantitative agreement between theoretical predictions and experiments. Notably, our results show that capillarity plays an important role for wavenumbers much smaller than expected from balancing elastic and capillary forces. We further confirm the efficiency of our approach by including the effect of gravity in our predictions and quantitatively comparing it to experiments.
- arXiv:1912.09832 (replaced) [pdf, ps, other]
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Title: Electron-phonon interaction and zero-field charge carrier transport in the nodal-line semimetal ZrSiSComments: Final version. 10 pages incl. Supplemental Material, 10 figuresJournal-ref: Phys. Rev. B 101, 115127 (2020)Subjects: Materials Science (cond-mat.mtrl-sci)
We study electron-phonon interaction and related transport properties of nodal-line semimetal ZrSiS using first-principles calculations. We find that ZrSiS is characterized by a weak electron-phonon coupling on the order of 0.1, which is almost energy independent. The main contribution to the electron-phonon coupling originates from long-wavelength optical phonons, causing no significant renormalization of the electron spectral function. At the charge neutrality point, we find that electrons and holes provide a comparable contribution to the scattering rate. The phonon-limited resistivity calculated within the Boltzmann transport theory is found to be strongly direction-dependent with the ratio between out-of-plane and in-plane directions being $\rho_{zz}/\rho_{xx}\sim 7.5$, mainly determined by the anisotropy of carrier velocities. We estimate zero-field resistivity to be $\rho_{xx}\approx12$ $\mu\Omega$ cm at 300 K, which is in good agreement with experimental data. Relatively small resistivity in ZrSiS can be attributed to a combination of weak electron-phonon coupling and high carrier velocities.
- arXiv:2001.01811 (replaced) [pdf, other]
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Title: Topologically controlled emergent dynamics in flow networksSubjects: Soft Condensed Matter (cond-mat.soft); Disordered Systems and Neural Networks (cond-mat.dis-nn); Pattern Formation and Solitons (nlin.PS)
Flow networks are essential for both living organisms and enginneered systems. These networks often present complex dynamics controlled, at least in part, by their topology. Previous works have shown that topologically complex networks interconnecting explicitly oscillatory or excitable elements can display rich emerging dynamics. Here we present a model for complex flow networks with non-linear conductance that allows for internal accumulation/depletion of volume, without any inherent oscillatory or excitable behavior at the nodes. In the absence of any time dependence in the pressure input and output we observe emerging dynamics in the form of self-sustained waves, which travel through the system. The frequency of these waves depends strongly on the network architecture and it can be explained with a topological metric.
- arXiv:2001.03175 (replaced) [pdf, other]
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Title: Crystal field Hamiltonian and anisotropy in KErSe2 and CsErSe2Comments: 5 pages 4 figures in main text, with 4 pages and 5 figures in appendicesJournal-ref: Phys. Rev. B 101, 144432 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el)
We use neutron scattering and bulk property measurements to determine the single-ion crystal-field Hamiltonians of delafossites $\rm KErSe_2$ and $\rm CsErSe_2$. These two systems contains planar equilateral triangular Er lattices arranged in two stacking variants: rhombohedral (for K) or hexagonal (Cs).
Our analysis shows that regardless the stacking order both compound exhibit an easy-plane ground state doublet with large $J_z=1/2$ terms and the potential for significant quantum effects, making them candidates for quantum spin liquid or other exotic ground states. - arXiv:2001.07929 (replaced) [pdf, other]
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Title: Fine structure of negatively charged and neutral excitons in monolayer MoS$_{2}$Authors: Joanna Jadczak, Joanna Kutrowska-Girzycka, Maciej Bieniek, Tomasz Kazimierczuk, Piotr Kossacki, Janina Schindler, Jörg Debus, Kenji Watanabe, Takashi Taniguchi, Ching-Hwa Ho, Arkadiusz Wójs, Paweł Hawrylak, Leszek BryjaSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci)
We present experimental and theoretical results on the high-quality single-layer MoS$_{2}$ which reveal the fine structure of charged excitons, i.e., trions. In the emission spectra we resolve and identify two trion peaks, T$_{1}$ and T$_{2}$, resembling the pair of singlet and triplet trion peaks (T$_S$ and T$_{T}$) in tungsten-based materials. However, in polarization-dependent photoluminescence measurements we identify these peaks as novel intra- and inter-valley singlet trions, constituting the trion fine structure distinct from that already known in bright and dark 2D materials with large conduction-band splitting induced by the spin-orbit coupling. We show that the trion energy splitting in MoS$_{2}$ is a sensitive probe of inter- and intra-valley carrier interaction. With additional support from theory we claim that the existence of these singlet trions combined with an anomalous excitonic g-factor and the characteristic temperature dependence of the emission spectra together suggest that monolayer MoS$_{2}$ has a dark excitonic ground state, despite having "bright" single-particle arrangement of spin-polarized conduction bands.
- arXiv:2001.08933 (replaced) [pdf]
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Title: Adaptive hard and tough mechanical response in single-crystal B1 VNx ceramics via control of anion vacanciesSubjects: Materials Science (cond-mat.mtrl-sci)
High hardness and toughness are generally considered mutually exclusive properties for single-crystal ceramics. Combining experiments and ab initio molecular dynamics (AIMD) atomistic simulations at room temperature, we demonstrate that both the hardness and toughness of single-crystal NaCl-structure VNx/MgO(001) thin films are simultaneously enhanced through the incorporation of anion vacancies. Nanoindentation results show that VN0.8, here considered as representative understoichiometric VNx system, is ~20% harder, as well as more resistant to fracture than stoichiometric VN samples. AIMD modeling of VN and VN0.8 supercells subjected to [001] and [110] elongation reveal that the tensile strengths of the two materials are similar. Nevertheless, while the stoichiometric VN phase systematically cleaves in a brittle manner at tensile yield points, the understoichiometric compound activates transformation-toughening mechanisms that dissipate accumulated stresses. AIMD simulations also show that VN0.8 exhibits an initially greater resistance to both {110}<1-10> and {111}<1-10> shear deformation than VN. However, for progressively increasing shear strains, the VN0.8 mechanical behavior gradually evolves from harder to more ductile than VN. The transition is mediated by anion vacancies, which facilitate {110}<1-10> and {111}<1-10> lattice slip by reducing activation shear stresses by as much as 35%. Electronic-structure analyses show that the two-regime hard/tough mechanical response of VN0.8 primarily stems from its intrinsic ability to transfer d electrons between 2nd-neighbor and 4th-neighbor (i.e., across vacancy sites) V-V metallic states. Our work offers a route for electronic-structure design of hard materials in which a plastic mechanical response is triggered with loading.
- arXiv:2001.09833 (replaced) [pdf]
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Title: Conditioning of Superconductive Properties in Graph-Shaped ReticlesComments: 18 pages and 6 figuresSubjects: Superconductivity (cond-mat.supr-con); Statistical Mechanics (cond-mat.stat-mech)
We report on phenomena observed in planar integrated networks obtained connecting superconducting island by Josephson tunnel junctions. These networks, identifiable as tree-like graphs, have branches consisting of series arrays of Josephson junctions which can be individually current biased and characterized. Both Josephson supercurrents and gap parameters of the arrays embedded in the graph structures display properties significantly different from those of reference arrays fabricated on the same chips and having identical geometrical shape. The temperature and magnetic field dependencies of the Josephson current of the embedded arrays both show a singular behavior when a critical value is reached by the Josephson characteristic energy. The gap parameter of the junctions generating the embedded arrays is higher than that of the junctions forming the reference geometrical arrays.
- arXiv:2001.10153 (replaced) [pdf, other]
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Title: A C/V$_2$O$_5$ core-sheath nanofibrous cathode with mixed-ion intercalation for aluminium-ion batteriesComments: Nano Express (2020)Subjects: Applied Physics (physics.app-ph); Materials Science (cond-mat.mtrl-sci); Chemical Physics (physics.chem-ph)
A new nanofibrous material, consisting of a conductive carbon core and an external layer made of vanadium oxide, has been studied as a cathode for aluminium-ion batteries. The material enables a mixed-ion intercalation mechanism, resulting in the alternating insertion of $\text{Al}^{3+}$ and $\text{AlCl}_4^-$ in the $\text{V}_2\text{O}_5$ and carbon layers, respectively. This is a highly desirable feature for cathode materials which may increase the energy density of future batteries by optimising the utilisation of the electrolyte.
- arXiv:2001.10653 (replaced) [pdf, other]
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Title: Dark-soliton molecules in an exciton-polariton superfluidAuthors: Anne Maître, Giovanni Lerario, Adrià Medeiros, Ferdinand Claude, Quentin Glorieux, Elisabeth Giacobino, Simon Pigeon, Alberto BramatiSubjects: Quantum Gases (cond-mat.quant-gas); Quantum Physics (quant-ph)
The general theory of dark solitons relies on repulsive interactions and therefore predicts the impossibility to form dark-soliton bound states. One important exception to this prediction is the observation of bound solitons in non-local nonlinear media. Here, we report that exciton-polariton superfluids can also sustain dark-soliton molecules although the interactions are fully local. With a novel all optical technique, we create two dark solitons and bind them to each other to form an unconventional dark-soliton molecule. We demonstrate that the stability of this structure and the separation distance between two dark-solitons is tightly connected to the driven-dissipative nature of the polariton fluid.
- arXiv:2001.10918 (replaced) [pdf, other]
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Title: Efficient orbital imaging based on ultrafast momentum microscopy and sparsity-driven phase retrievalAuthors: G. S. M. Jansen, M. Keunecke, M. Düvel, C. Möller, D. Schmitt, W. Bennecke, F. J. S. Kappert, D. Steil, D. R. Luke, S. Steil, S. MathiasSubjects: Materials Science (cond-mat.mtrl-sci); Chemical Physics (physics.chem-ph)
We present energy-resolved photoelectron momentum maps for orbital tomography that have been collected with a novel and efficient time-of-flight momentum microscopy setup. This setup is combined with a 0.5 MHz table-top femtosecond extreme-ultraviolet light source, which enables unprecedented speed in data collection and paves the way towards time-resolved orbital imaging experiments in the future. Moreover, we take a significant step forward in the data analysis procedure for orbital imaging, and present a sparsity-driven approach to the required phase retrieval problem, which uses only the number of non-zero pixels in the orbital. Here, no knowledge of the object support is required, and the sparsity number can easily be determined from the measured data. Used in the relaxed averaged alternating reflections algorithm, this sparsity constraint enables fast and reliable phase retrieval for our experimental as well as noise-free and noisy simulated photoelectron momentum map data.
- arXiv:2001.11313 (replaced) [pdf]
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Title: Neutron inelastic scattering study of rare-earth orthoferrite HoFeO$_3$Subjects: Materials Science (cond-mat.mtrl-sci); Strongly Correlated Electrons (cond-mat.str-el)
By the single crystal inelastic neutron scattering the orthoferrite HoFeO3 was studied. We show that the spin dynamics of the Fe subsystem does not change through the spin-reorientation transitions. The observed spectrum of magnetic excitations was analyzed in the frames of linear spin-wave theory. Within this approach the antiferromagnetic exchange interactions of nearest neighbors and next nearest neighbors were obtained for Fe subsystem. Parameters of Dzyaloshinskii-Moriya interactions at Fe subsystem were refined. The temperature dependence of the gap in Fe spin-wave spectrum indicates the temperature evolution of the anisotropy parameters. The estimations for the values of Fe-Ho and Ho-Ho exchange interaction were made as well.
- arXiv:2001.11638 (replaced) [pdf, ps, other]
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Title: Electron and Light Induced Stimulated Raman Spectroscopy for Nanoscale Molecular MappingComments: 7 pages, 4 figures, Amr A. E. Saleh and Daniel K. Angell contributed equally to this workSubjects: Optics (physics.optics); Materials Science (cond-mat.mtrl-sci)
We propose and theoretically analyze a new vibrational spectroscopy, termed electron- and light-induced stimulated Raman (ELISR) scattering, that combines the high spatial resolution of electron microscopy with the molecular sensitivity of surface-enhanced Raman spectroscopy. With ELISR, electron-beam excitation of plasmonic nanoparticles is utilized as a spectrally-broadband but spatially-confined Stokes beam in the presence of a diffraction-limited pump laser. To characterize this technique, we develop a numerical model and conduct full-field electromagnetic simulations to investigate two distinct nanoparticle geometries, nanorods and nanospheres, coated with a Raman-active material. Our results show the significant ($10^6$-$10^7$) stimulated Raman enhancement that is achieved with dual electron and optical excitation of these nanoparticle geometries. Importantly, the spatial resolution of this vibrational spectroscopy for electron microscopy is solely determined by the nanoparticle geometry and the plasmon mode volume. Our results highlight the promise of ELISR for simultaneous high-resolution electron microscopy with sub-diffraction-limited Raman spectroscopy, complementing advances in superresolution microscopy, correlated light and electron microscopy, and vibrational electron energy loss spectroscopy.
- arXiv:2002.03000 (replaced) [pdf, other]
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Title: Parallel PERMSubjects: Statistical Mechanics (cond-mat.stat-mech); Soft Condensed Matter (cond-mat.soft)
We develop and implement a parallel flatPERM algorithm \cite{G97,PK04} with mutually interacting parallel flatPERM sequences and use it to sample self-avoiding walks in 2 and 3 dimensions. Our data show that the parallel implementation accelerates the convergence of the flatPERM algorithm. Moreover, increasing the number of interacting flatPERM sequences (rather than running longer simulations) improves the rate of convergence. This suggests that a more efficient implementation of flatPERM will be a massively parallel implementation, rather than long simulations of one, or a few parallel sequences. We also use the algorithm to estimate the growth constant of the self-avoiding walk in two and in three dimensions using simulations over 12 parallel sequences. Our best results are \[ \mu_d = \cases{ 2.6381585(1), & \hbox{if $d=2$}; \cr 4.684039(1), & \hbox{if $d=3$}. } \]
- arXiv:2002.05251 (replaced) [pdf]
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Title: A Step Forward from High-Entropy Ceramics to Compositionally Complex Ceramics: A New PerspectiveComments: 32 pages, 6 figuresJournal-ref: The Special 1000th Issue of the Journal of Materials Science (2020)Subjects: Materials Science (cond-mat.mtrl-sci)
High-entropy ceramics (HECs) have quickly gained attention since 2015. To date, nearly all work has focused on five-component, equimolar compositions. This perspective article briefly reviews different families of HECs and selected properties. Following a couple of our most recent studies, we propose a step forward to expand HECs to Compositionally Complex ceramics (CCCs) to include medium-entropy and non-equimolar compositions. Using defective fluorite and ordered pyrochlore oxides as two primary examples, we further consider the complexities of aliovalent cations and anion vacancies as well as ordered structures with two cation sublattices. Better thermally-insulating yet stiff CCCs have been found in non-equimolar compositions with optimal amounts of oxygen vacancies and in ordered pyrochlores with substantial size disorder. It is demonstrated that medium-entropy ceramics (MECs) can prevail over their high-entropy counterparts. The diversifying classes of CCCs provide even more possibilities than HECs to tailor the composition, defects, disorder/order, and, consequently, various properties.
- arXiv:2002.05312 (replaced) [pdf]
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Title: Polar state of 0.67BiFeO3-0.33BaTiO3 near the morphotropic phase boundarySubjects: Materials Science (cond-mat.mtrl-sci)
The symmetric studies on the structure-property relationship of the unpoled and poled states of 0.67BiFeO3-0.33BaTiO3 (0.67BF-0.33BT) were conducted to understand the origin of the morphotropic phase boundary (MPB) in BF-BT. A typical relaxor-type dielectric anomaly was observed (Tf, ~627 K). The remnant polarization (Pr) and maximum value of electro-strain (Sm) increase clearly during heating (Pr, ~40 uC/cm2; Sm, 0.191 % under 40 kV/cm at 453 K). The first-cycle electro-strain loops indicate the difference in the polar state between 0.67BF-0.33BT and 0.94BiNaTiO3-0.06BaTiO3. Both the unpoled and poled samples have the similar frequency dispersion behaviors. Even in the poled samples, the transition between the ergodic relaxor state and ferroelectric-like state does not involve a clear dielectric anomaly. Analyses based on the Rietveld refinement of XRD patterns, bright-field images and selected-area electron diffractions (SAED) demonstrated that the formation of the long-range ferroelectric domains was difficult under the poling field.
- arXiv:2002.06167 (replaced) [pdf, other]
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Title: Tuning the electronic structure and magnetoresistance in a semi-metallic system by dimensional confinementAuthors: Shouvik Chatterjee, Shoaib Khalid, Hadass S. Inbar, Taozhi Guo, Yu-Hao Chang, Elliot Young, Alexei V. Fedorov, Dan Read, Anderson Janotti, Christopher J. PalmstrømComments: 7 pages, 4 figures, Supplementary Information 8 pages, 10 figuresSubjects: Materials Science (cond-mat.mtrl-sci); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Observation of large, non-saturating magnetoresistance, tunable magnetic structure and possible realization of topologically non-trivial states make semi-metallic rare-earth monopnictides an attractive material system for basic and applied sciences. Here, utilizing a combination of angle-resolved photoemission spectroscopy, magneto-transport measurements and first-principles calculations we show that the electronic structure and material properties of these compounds can be significantly modified in few atomic layer geometries. Our observation reveals that dimensional confinement in heteroepitaxial LuSb thin films lifts the carrier compensation and differentially affects the mobility of the electron and hole-like carriers leading to a strong modification in the magnetoresistance behavior from its bulk limit, thus establishing the role of electron-hole compensation in its magnetoresistance behavior. We unambiguously establish that LuSb remains semi-metallic at least till the ultra-thin limit of 3 unit cells (1.8 nm). Observed upturn in resistivity at low temperatures in few atomic layer geometries results from strong electron-electron interaction effects and should not be construed as indicative of opening of a bulk band gap.
- arXiv:2002.06210 (replaced) [pdf, other]
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Title: Scaling of variational quantum circuit depth for condensed matter systemsComments: 11 + 4 pages, 5 figuresJournal-ref: Quantum 4, 272 (2020)Subjects: Quantum Physics (quant-ph); Statistical Mechanics (cond-mat.stat-mech); High Energy Physics - Theory (hep-th)
We benchmark the accuracy of a variational quantum eigensolver based on a finite-depth quantum circuit encoding ground state of local Hamiltonians. We show that in gapped phases, the accuracy improves exponentially with the depth of the circuit. When trying to encode the ground state of conformally invariant Hamiltonians, we observe two regimes. A finite-depth regime, where the accuracy improves slowly with the number of layers, and a finite-size regime where it improves again exponentially. The cross-over between the two regimes happens at a critical number of layers whose value increases linearly with the size of the system. We discuss the implication of these observations in the context of comparing different variational ansatz and their effectiveness in describing critical ground states.
- arXiv:2002.09965 (replaced) [pdf, ps, other]
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Title: Brownian flights over a circleComments: 7 pages, 1 figureSubjects: Probability (math.PR); Statistical Mechanics (cond-mat.stat-mech)
The stationary radial distribution, $P(\rho)$, of the random walk with the diffusion coefficient $D$, which winds with the tangential velocity $V$ around the impenetrable disc of radius $R$ for $R\gg 1$ converges to the distribution involving the Airy function. Typical trajectories are localized in the circular strip $[R, R+ \delta R^{1/3}]$, where $\delta$ is the constant which depends on the parameters $D$ and $V$ and is independent on $R$.
- arXiv:2002.11690 (replaced) [pdf, other]
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Title: Many faces of nonequilibrium: anomalous transport phenomena in driven periodic systemsComments: in press in the special issue of Acta Physica Polonica BJournal-ref: Acta Physica Polonica B 51, 1131 (2020)Subjects: Statistical Mechanics (cond-mat.stat-mech); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Soft Condensed Matter (cond-mat.soft)
We consider a generic system operating under non-equilibrium conditions. Explicitly, we consider an inertial classical Brownian particle dwelling a periodic structure with a spatially broken reflection symmetry. The particle is coupled to a bath at the temperature $T$ and is driven by an unbiased time-periodic force. In the asymptotic long time regime the particle operates as a Brownian motor exhibiting finite directed transport although no net biasing force acts on the system. Here we review and interpret in further detail recent own research on the peculiar transport behaviour for this setup. The main focus is put on those different emerging Brownian diffusion anomalies. Particularly, within the transient, time-dependent domain the particle is able to exhibit anomalous diffusive motion which eventually crosses over into normal diffusion only in the asymptotic long-time limit. In the latter limit this normal diffusion coefficient may even show a non-monotonic temperature dependence, meaning that it is not monotonically increasing with increasing temperature, but may exhibit instead an extended, intermediate minimum before growing again with increasing temperature.
- arXiv:2002.12230 (replaced) [pdf, other]
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Title: Nickelate superconductors -- a renaissance of the one-band Hubbard modelComments: 6+10 pages. In the second version we also compare to the experimental phase diagram [arXiv:2003.08506] in the Supplemetary Information Section S.6Subjects: Superconductivity (cond-mat.supr-con); Strongly Correlated Electrons (cond-mat.str-el)
Following the discovery of superconductivity in the cuprates and the seminal work by Anderson, the theoretical efforts to understand high-temperature superconductivity have been focusing to a large extent on a simple model: the one-band Hubbard model. However, superconducting cuprates need to be doped, and the doped holes go into the oxygen orbitals. This requires a more elaborate multi-band model such as the three-orbital Emery model. The recently discovered nickelate superconductors appear, at first glance, to be even more complicated multi-orbital systems. Here, we analyse this multi-orbital system and find that it is instead the nickelates which can be described by a one-band Hubbard model, albeit with an additional electron reservoir and only around the superconducting regime. Our calculations of the critical temperature Tc are in good agreement with experiment, and show that optimal doping is slightly below the 20% Sr-doping of Ref. 11. Even more promising than 3d nickelates are 4d palladates.
- arXiv:2002.12310 (replaced) [pdf, other]
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Title: Visualizing Correlations in the 2D Fermi-Hubbard Model with AIAuthors: Ehsan Khatami, Elmer Guardado-Sanchez, Benjamin M. Spar, Juan Felipe Carrasquilla, Waseem S. Bakr, Richard T. ScalettarComments: 26 pages, 20 figures; added Figs. 3 & 16, updated the text and referencesSubjects: Strongly Correlated Electrons (cond-mat.str-el); Disordered Systems and Neural Networks (cond-mat.dis-nn); Quantum Gases (cond-mat.quant-gas)
Strongly correlated phases of matter are often described in terms of straightforward electronic patterns. This has so far been the basis for studying the Fermi-Hubbard model realized with ultracold atoms. Here, we show that artificial intelligence (AI) can provide an unbiased alternative to this paradigm for phases with subtle, or even unknown, patterns. Long and short range spin correlations spontaneously emerge in filters of a convolutional neural network trained on snapshots of single atomic species. In the less well-understood strange metallic phase of the model, we find that a more complex network trained on snapshots of local moments produces an effective order parameter for the non-Fermi liquid behavior. Our technique can be employed to characterize correlations unique to other phases with no obvious order parameters or signatures in projective measurements, and has implications for science discovery through AI beyond strongly correlated systems.
- arXiv:2003.00165 (replaced) [pdf, other]
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Title: Entanglement transfer from quantum matter to classical geometry in an emergent holographic dual description of a scalar field theorySubjects: High Energy Physics - Theory (hep-th); Strongly Correlated Electrons (cond-mat.str-el)
Applying recursive renormalization group transformations to a scalar field theory, we obtain an effective quantum gravity theory with an emergent extra dimension, described by a dual holographic Einstein-Klein-Gordon action. In the large $N$ limit, where $N$ is the flavor number of the original scalar fields, quantum fluctuations of both dynamical metric and dual scalar fields are suppressed, leading to a classical field theory of the Einstein-scalar type in $(D+1)$-spacetime dimensions. We show that this emergent background gravity describes the renormalization group flows of coupling functions in the UV quantum field theory through the extra dimension. More precisely, the IR boundary conditions of the Einstein equations, given by the Gibbons-Hawking-York action, correspond to the renormalization group $\beta$-functions of the quantum field theory, where the infinitesimal distance in the extra-dimensional space is identified with an energy scale for the renormalization group transformation. Finally, we also show that this dual holographic formulation describes quantum entanglement in a geometrical way, encoding the transfer of quantum entanglement from quantum matter to classical gravity in the large $N$ limit. We claim that this entanglement transfer serves as a microscopic foundation for the emergent holographic duality description.
- arXiv:2003.01019 (replaced) [pdf, other]
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Title: Simulating the Shastry-Sutherland Ising Model using Quantum AnnealingAuthors: Paul Kairys, Andrew D. King, Isil Ozfidan, Kelly Boothby, Jack Raymond, Arnab Banerjee, Travis S. HumbleComments: 16 pages, 4 figures, code available at this https URLSubjects: Quantum Physics (quant-ph); Materials Science (cond-mat.mtrl-sci); Statistical Mechanics (cond-mat.stat-mech)
Frustration represents an essential feature in the behavior of magnetic materials when constraints on the microscopic Hamiltonian cannot be satisfied simultaneously. This gives rise to exotic phases of matter including spin liquids, spin ices, and stripe phases. Here we demonstrate an approach to understanding the microscopic effects of frustration by computing the phases of a 468-spin Shastry-Sutherland Ising Hamiltonian using a quantum annealer. Our approach uses mean-field boundary conditions to mitigate effects of finite size and defects alongside an iterative quantum annealing protocol to simulate statistical physics. We recover all phases of the Shastry-Sutherland Ising model -- including the well-known fractional magnetization plateau -- and the static structure factor characterizing the critical behavior at these transitions. These results establish quantum annealing as an emerging method in understanding the effects of frustration on the emergence of novel phases of matter and pave the way for future comparisons with real experiments.
- arXiv:2003.03800 (replaced) [pdf, ps, other]
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Title: One or two small points in thermodynamicsAuthors: Walter F. WreszinskiComments: 33 pages, important conceptual additions and corrections in section 5Subjects: Statistical Mechanics (cond-mat.stat-mech); Mathematical Physics (math-ph)
I present my recollections of what I used to find to be "one or two small points in thermodynamics", following Sommerfeld's famous quote, and review them on the light of present knowledge.
- arXiv:2003.04324 (replaced) [pdf, ps, other]
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Title: Intertwined Order in Fractional Chern Insulators from Finite-Momentum Pairing of Composite FermionsComments: 15 pages, 11 figures. v2: updated references and acknowledgmentsSubjects: Strongly Correlated Electrons (cond-mat.str-el)
We investigate the problem of intertwined orders in fractional Chern insulators by considering lattice fractional quantum Hall (FQH) states arising from pairing of composite fermions in the square-lattice Hofstadter model. At certain filling fractions, magnetic translation symmetry ensures the composite fermions form Fermi surfaces with multiple pockets, leading to the formation of finite-momentum Cooper pairs in the presence of attractive interactions. We obtain mean-field phase diagrams exhibiting a rich array of striped and topological phases, establishing paired lattice FQH states as an ideal platform to investigate the intertwining of topological and conventional broken symmetry order.
- arXiv:2003.05401 (replaced) [pdf, other]
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Title: Correlated Disorder in the SYK$_{2}$ modelComments: 27 pages, 13 figures, minor changes, reference addedSubjects: High Energy Physics - Theory (hep-th); Statistical Mechanics (cond-mat.stat-mech); Quantum Physics (quant-ph)
We study the SYK$_{2}$ model of $N$ Majorana fermions with random quadratic interactions through a detailed spectral analysis and by coupling the model to 2- and 4-point sources. In particular, we define the generalized spectral form factor and level spacing distribution function by generalizing from the partition function to the generating function. For $N=2$, we obtain an exact solution of the generalized spectral form factor. It exhibits qualitatively similar behavior to the higher $N$ case with a source term, this exact solution helps to understand the behavior of the generalized spectral form factor. We calculate the generalized level spacing distribution function and the mean value of the adjacent gap ratio defined by the generating function. We find a Gaussian unitary ensemble for the SYK$_2$ model with a 4-point source term in a near-integrable region of the theory indicating a transition to chaos. This chaotic property might be expected to be more evident with stronger source terms. On the contrary, we find a departure from random matrix behavior as the source term is enhanced.
- arXiv:2003.07400 (replaced) [pdf, ps, other]
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Title: Impressive Electronic Transport in Be$_2$C Monolayer Limited by PhononComments: 19 pages, 7 figuresSubjects: Materials Science (cond-mat.mtrl-sci)
We present thermoelectric properties of Be$_2$C monolayer based on density functional theory combined with semi-classical Boltzmann transport theory. First principles calculations show the material is direct band gap semiconductor with band gap of 2.0 eV obtained with Gaussian-attenuating Perdew-Burke-Ernzerhof (Gau-PBE) hybrid functionals. Kohn-Sham eigen-states obtained with Gau-PBE are fed into Boltzmann transport equation which is solved under constant relaxation time approximation resulting into thermoelectric (TE) coefficient in terms of the relaxation time ($\tau$). In this work, we have explicitly determined the relaxation time by studying the electron-phonon interactions from first principles using Wannier functions to obtain the absolute TE coefficients for the Be$_2$C monolayer along the armchair and zigzag directions. Our results show that the Be$_2$C monolayer has high TE coefficients like Seebeck coefficient ($\alpha$) and electrical conductivity ($\sigma$) leading to high power factor ($\alpha^2\sigma$ $\sim$ 3.44 mW/mK$^2$) along the zigzag direction with p-type doping which is of the similar order observed for the commercial TE materials like doped-Bi$_2$Te$_3$ (J. Appl. Phys. 2003 (93) 368-374; J. Appl. Phys. 2008 (104) 053713-1-053713-5). Further, third-order anharmonic theory yields the slightly high lattice thermal conductivity ($\sim$ 66 W/mK) at 300 K giving rise to moderate figure of merit (ZT $\sim$ 0.1) optimized with p-type doping along the zigzag direction. Our results suggest that Be$_2$C monolayer is promising material for thermoelectric applications as far as high power factor is concerned. Additionally, the dynamical stability of the Be$_2$C monolayer up to 14 \% bi-axial strain shows that phonon tranport in the Be$_2$C monolayer can be further improved through strain engineering.
- arXiv:2003.07643 (replaced) [pdf, other]
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Title: Solution landscape of a reduced Landau-de Gennes model on a hexagonComments: 15 pages, 10 figuresSubjects: Mathematical Physics (math-ph); Soft Condensed Matter (cond-mat.soft)
We investigate the solution landscape of a reduced Landau--de Gennes model for nematic liquid crystals on a two-dimensional hexagon at a fixed temperature, as a function of $\lambda$---the edge length. This is a generic example for reduced approaches on regular polygons. We apply the high-index optimization-based shrinking dimer method to systematically construct the solution landscape consisting of multiple defect solutions and relationships between them. We report a new stable T state with index-$0$ that has an interior $-1/2$ defect; new classes of high-index saddle points with multiple interior defects referred to as H class and TD class; changes in the Morse index of saddle points with $\lambda^2$ and novel pathways mediated by high-index saddle points that can control and steer dynamical pathways. The range of topological degrees, locations and multiplicity of defects offered by these saddle points can be used to navigate through complex solution landscapes of nematic liquid crystals and other related soft matter systems.
- arXiv:2003.07875 (replaced) [pdf, ps, other]
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Title: Statistics of work performed by optical tweezers with general time-variation of their stiffnessComments: 21 pages, 4 figuresSubjects: Statistical Mechanics (cond-mat.stat-mech)
We derive an exact expression for the probability density of work done on a particle that diffuses in a parabolic potential with a stiffness varying by an arbitrary piecewise constant protocol. Based on this result, the work distribution for time-continuous protocols of the stiffness can be determined up to any degree of accuracy. This is achieved by replacing the continuous driving by a piecewise constant one with a number $n$ of positive or negative steps of increasing or decreasing stiffness. With increasing $n$, the work distributions for the piecewise protocols approach that for the continuous protocol. The moment generating function of the work is given by the inverse square root of a polynomial of degree $n$, whose coefficients are efficiently calculated from a recurrence relation. The roots of the polynomials are real and positive (negative) steps of the protocol are associated with negative (positive) roots. Using these properties the inverse Laplace transform of the moment generating function is carried out explicitly. Fluctuation theorems are used to derive further properties of the polynomials and their roots.
- arXiv:2003.08140 (replaced) [pdf]
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Title: Experimental discovery of bulk-disclination correspondenceSubjects: Materials Science (cond-mat.mtrl-sci); Optics (physics.optics)
The past decade has witnessed the emergence of abundant topological phases protected by crystalline symmetries, such as topological crystalline insulators (TCIs) [1-3]. Recent discoveries of higher-order [4-7] and fragile [8-11] TCIs illustrate that gapless edge states may not be a universal feature of TCIs, and thus request alternative experimental signatures. Here, we demonstrate that disclinations, i.e., rotational topological defects in crystals, can serve as a novel probe of TCIs without invoking edge boundaries. Using photonic crystals, i.e., artificial periodic structures giving access to versatile manipulations of light [12], we observe topologically-protected photonic modes localized at disclinations in photonic TCIs. We create physical realizations of photonic TCIs and disclinations using macroscopic dielectric structures based on hexagonal lattices. By driving the photonic system across a topological transition through tuning the unit-cell geometry, we find that the topological disclination modes disappear in the trivial phase. The experimental discovery of the bulk-disclination correspondence unveils a new horizon in topological physics, while its photonic realization provides a pathway toward topological photonics [13-23] beyond the bulk-edge correspondence.
- arXiv:2003.08868 (replaced) [pdf]
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Title: Ostwald growth rate in controlled Covid-19 epidemic spreading as in arrested growth in quantum complex matterComments: 2 figures, 7 pagesJournal-ref: Condens. Matter 2020, 5, 23Subjects: Physics and Society (physics.soc-ph); Other Condensed Matter (cond-mat.other); Populations and Evolution (q-bio.PE)
Here, we focus on the data analysis of the growth of epidemic spread of Covid-19 in countries where different policies of containment were activated. It is known that the growth of pandemic spread at its threshold is exponential, but it is not known how to quantify the success of different containment policies. We identify that a successful approach gives an arrested phase regime following the Ostwald growth, where, over the course of time, one phase transforms into another metastable phase with a similar free energy as observed in oxygen interstitial diffusion in quantum complex matter and in crystallization of proteins. We introduce the s factor which provides a quantitative measure of the efficiency and speed of the adopted containment policy, which is very helpful not only to monitor the Covid-19 pandemic spread but also for other countries to choose the best containment policy. The results show that a policy based on joint confinement, targeted tests, and tracking positive cases is the most rapid pandemic containment policy; in fact, we found values of 9, 5, and 31 for the success s factor for China, South Korea, and Italy, respectively, where the lowest s factor indicates the best containment policy
- arXiv:1712.08932 (replaced) [pdf, ps, other]
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Title: Universal shape characteristics for the mesoscopic star-shaped polymer via dissipative particle dynamics simulationsJournal-ref: J. Phys.: Cond.Matt. vol. 30 (2018) 215101Subjects: Soft Condensed Matter (cond-mat.soft)
In this paper we study the shape characteristics of star-like polymers in various solvent quality using a mesoscopic level of modeling. The dissipative particle dynamics simulations are performed for the homogeneous and four different heterogeneous star polymers with the same molecular weight. We analyse the gyration radius and asphericity at the bad, good and $\theta$-solvent regimes. Detailed explanation based on interplay between enthalpic and entropic contributions to the free energy and analyses on of the asphericity of individual branches are provided to explain the increase of the apsphericity in $\theta$-solvent regime.
- arXiv:1806.02569 (replaced) [pdf, other]
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Title: Classical phase transitions in a one-dimensional short-range spin model induced by entropy depletion or complex fieldsComments: 29 pages, 11 figuresJournal-ref: Journ. Phys. A vol. 51 (2018) 505001Subjects: Statistical Mechanics (cond-mat.stat-mech)
Ising's solution of a classical spin model famously demonstrated the absence of a positive-temperature phase transition in one-dimensional equilibrium systems with short-range interactions. No-go arguments established that the energy cost to insert domain walls in such systems is outweighed by entropy excess so that symmetry cannot be spontaneously broken. An archetypal way around the no-go theorems is to augment interaction energy by increasing the range of interaction. Here we introduce new ways around the no-go theorems by investigating entropy depletion instead. We implement this for the Potts model with invisible states.Because spins in such a state do not interact with their surroundings, they contribute to the entropy but not the interaction energy of the system. Reducing the number of invisible states to a negative value decreases the entropy by an amount sufficient to induce a positive-temperature classical phase transition. This approach is complementary to the long-range interaction mechanism. Alternatively, subjecting positive numbers of invisible states to imaginary or complex fields can trigger such a phase transition. We also discuss potential physical realisability of such systems.
- arXiv:1811.05514 (replaced) [pdf]
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Title: Symmetry-protected hierarchy of anomalous multipole topological band gaps in nonsymmorphic metacrystalsAuthors: Xiujuan Zhang, Zhi-Kang Lin, Hai-Xiao Wang, Zhan Xiong, Yuan Tian, Ming-Hui Lu, Yan-Feng Chen, Jian-Hua JiangComments: 5 figures. Accepted by Nature CommunicationsJournal-ref: Nature Communications 11, 65 (2020)Subjects: Materials Science (cond-mat.mtrl-sci); Classical Physics (physics.class-ph)
Symmetry and topology are two fundamental aspects of many quantum states of matter. Recently, new topological materials, higher-order topological insulators, were discovered, featuring, e.g., bulk-edge-corner correspondence that goes beyond the conventional topological paradigms. Here, we discover experimentally that the nonsymmorphic $p4g$ acoustic metacrystals host a symmetry-protected hierarchy of topological multipoles: the lowest band gap has a quantized Wannier dipole and can mimic the quantum spin Hall effect, while the second band gap exhibits quadrupole topology with anomalous Wannier bands. Such a topological hierarchy allows us to observe experimentally distinct, multiplexing topological phenomena and to reveal a topological transition triggered by the geometry-transition from the $p4g$ group to the $C_{4v}$ group which demonstrates elegantly the fundamental interplay between symmetry and topology. Our study demonstrates an instance that classical systems with controllable geometry can serve as powerful simulators for the discovery of novel topological states of matter and their phase transitions.
- arXiv:1811.06750 (replaced) [pdf, ps, other]
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Title: Itô vs Stratonovich in the presence of absorbing statesComments: Accepted in the Journal of Mathematical PhysicsJournal-ref: J. Math. Phys. 60, 123301 (2019)Subjects: Probability (math.PR); Statistical Mechanics (cond-mat.stat-mech); Mathematical Physics (math-ph)
It is widely assumed that there exists a simple transformation from the It\^o interpretation to the one by Stratonovich and back for any stochastic differential equation of applied interest. While this transformation exists under suitable conditions, and transforms one interpretation into the other at the price of modifying the drift of the equation, it cannot be considered universal. We show that a class of stochastic differential equations, characterized by the presence of absorbing states and of interest in applications, does not admit such a transformation. In particular, formally applying this transformation may lead to the disappearance of some absorbing states. In turn, this modifies the long-time, and even the intermediate-time, behavior of the solutions. The number of solutions can also be modified by the unjustified application of the mentioned transformation, as well as by a change in the interpretation of the noise. We discuss how these facts affect the classical debate on the It\^o vs Stratonovich dilemma.
- arXiv:1812.05978 (replaced) [pdf]
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Title: Experimental evidence of monolayer arsenene: An exotic two-dimensional semiconducting materialJournal-ref: 2D Mater. 7, 025013 (2020)Subjects: Materials Science (cond-mat.mtrl-sci)
Group V element analogues of graphene have attracted a lot attention recently due to their semiconducting band structures, which make them promising for next generation electronic and optoelectronic devices based on two-dimensional materials. Theoretical investigations predict high electron mobility, large band gaps, band gap tuning by strain, formation of topological phases, quantum spin Hall effect at room temperature, and superconductivity amongst others. Here, we report a successful formation of freestanding like monolayer arsenene on Ag(111). This was concluded from our experimental atomic and electronic structure data by comparing to results of our theoretical calculations. Arsenene forms a buckled honeycomb layer on Ag(111) with a lattice constant of 3.6 {\AA} showing an indirect band gap of about 1.4 eV as deduced from the position of the Fermi level pinning.
- arXiv:1812.11799 (replaced) [pdf, other]
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Title: Disordered contacts can localize chiral edge electronsComments: 8 pages, 7 figuresJournal-ref: Journal of Physics and Chemistry of Solids 139, 109313 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Chiral integer quantum Hall (QH) edge modes are immune to backscattering and therefore are non-localized and show a vanishing longitudinal as well as non-local resistance along with quantized 2-terminal and Hall resistance even in the presence of sample disorder. However, this is not the case for contact disorder, which refers to the possibility that a contact can reflect edge modes either partially or fully. This paper shows that when all contacts are disordered in a N-terminal quantum Hall bar, then transport via chiral QH edge modes can have a significant localization correction. The Hall and 2-terminal resistance in an N-terminal quantum Hall sample deviate from their values derived while neglecting the phase acquired at disordered contacts, and this deviation is called the quantum localization correction. This correction term increases with the increase of disorderedness of contacts but decreases with the increase in the number of contacts in an N-terminal Hall bar. The presence of inelastic scattering, however, can completely destroy the quantum localization correction.
- arXiv:1902.06573 (replaced) [pdf]
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Title: Expanding the horizon of automated metamaterials discovery via quantum annealingComments: 26pages, 5 figuresJournal-ref: Phys. Rev. Research 2, 013319 (2020)Subjects: Applied Physics (physics.app-ph); Materials Science (cond-mat.mtrl-sci); Computational Physics (physics.comp-ph)
Complexity of materials designed by machine learning is currently limited by the inefficiency of classical computers. We show how quantum annealing can be incorporated into automated materials discovery and conduct a proof-of-principle study on designing complex thermofunctional metamaterials consisting of SiO2, SiC, and Poly(methyl methacrylate). Empirical computing time of our quantum-classical hybrid algorithm involving a factorization machine, a rigorous coupled wave analysis, and a D-Wave 2000Q quantum annealer was insensitive to the problem size, while a classical counterpart experienced rapid increase. Our method was used to design complex structures of wavelength selective radiators showing much better concordance with the thermal atmospheric transparency window in comparison to existing human-designed alternatives. Our result shows that quantum annealing provides scientists gigantic computational power that may change how materials are designed.
- arXiv:1904.02929 (replaced) [pdf, other]
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Title: Simulation of dense non-Brownian suspensions with the lattice Boltzmann method: Shear jammed and fragile statesJournal-ref: Soft Matter, 2020,16, 945-959Subjects: Soft Condensed Matter (cond-mat.soft)
Dense non-Brownian suspensions including both the hydrodynamic interactions and the frictional contacts between particles are numerically studied under simple and oscillatory shears in terms of the lattice Boltzmann method. We successfully reproduce the discontinuous shear thickening (DST) under a simple shear for bulk three-dimensional systems. For our simulation of an oscillatory shear in a quasi-two-dimensional system, we measure the mechanical response when we reduce the strain amplitude after the initial oscillations with a larger strain amplitude. Here, we find the existence of the shear-jammed state under this protocol in which the storage modulus $G^{\prime}$ is only finite for high initial strain amplitude $\gamma_0^{I}$. We also find the existence of the fragile state in which both fluid-like and solid-like responses can be detected for an identical area fraction and an initial strain amplitude $\gamma_0^{I}$ depending on the initial phase $\Theta$ (or the asymmetricity of the applied strain) of the oscillatory shear. We also observe the DST-like behavior under the oscillatory shear in the fragile state. Moreover, we find that the stress anisotropy becomes large in the fragile state. Finally, we confirm that the stress formula based on the angular distribution of the contact force recovers the contact contributions to the stress tensors for both simple and oscillatory shears with large strains.
- arXiv:1904.05241 (replaced) [pdf, other]
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Title: Rate dependence of current and fluctuations in jump models with negative differential mobilitySubjects: Statistical Mechanics (cond-mat.stat-mech)
Negative differential mobility is the phenomenon in which the velocity of a particle decreases when the force driving it increases. We study this phenomenon in Markov jump models where a particle moves in the presence of walls that act as traps. We consider transition rates that obey local detailed balance but differ in normalisation, the inclusion of a rate to cross a wall and a load factor. We illustrate the full counting statistics for different choices of the jumping rates. We also show examples of thermodynamic uncertainty relations. The variety of behaviours we encounter highlights that negative differential mobility depends crucially on the chosen rates and points out the necessity that such choices should be based on proper coarse-graining studies of a more microscopic description.
- arXiv:1906.04696 (replaced) [pdf]
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Title: Thermal conductivity and thermal rectification of nanoporous graphene: A molecular dynamics simulationComments: 17 pages, 8 figuresJournal-ref: International Journal of Heat and Mass Transfer 146 (2020): 118884Subjects: Computational Physics (physics.comp-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Using non-equilibrium molecular dynamics (NEMD) simulation, we study thermal properties of the so-called nanoporous graphene (NPG) sheet which contains a series of nanoporous in an ordered way and was synthesized recently (Science 360 (2018), 199). The dependence of thermal conductivity on sample size, edge chirality, and porosity concentration are investigated. Our results indicate that the thermal conductivity of NPG is about two orders smaller compared with of pristine graphene. Therefore this sheet can be used as a thermoelectric material. Also, the porosity concentration helps us to tune the thermal conductivity. Moreover, the results show that the thermal conductivity increases with growing sample length due to ballistic transport. On the other hand, along the armchair direction, the thermal conductivity is larger than zigzag direction. We also examined the thermal properties of the interface of NPG and graphene. The temperature drops significantly through the interface leading to the thermal resistance. The thermal resistance changes with imposed heat flux direction, and this difference cause significantly large thermal rectification factor, and heat current prefers one direction to another. Besides, to investigate those quantities fundamentally, we study the phonon density of states and scattering of them.
- arXiv:1908.05158 (replaced) [pdf, other]
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Title: Criticality of Spin Systems with Weak Long-Range InteractionsComments: 24 pages, 5 figures, Submitted to the special issue of J. Phys. A on 'Long-range Interactions and Synchronization'Journal-ref: J. Phys. A: Math. Theor. 53 143001 (2020)Subjects: Statistical Mechanics (cond-mat.stat-mech); Quantum Gases (cond-mat.quant-gas); Quantum Physics (quant-ph)
The study of critical properties of systems with long-range interactions has attracted in the last decades a continuing interest and motivated the development of several analytical and numerical techniques, in particular in connection with spin models. From the point of view of the investigation of their criticality, a special role is played by systems in which the interactions are long-range enough that their universality class is different from the short-range case and, nevertheless, they maintain the extensivity of thermodynamical quantities. Such interactions are often called weak long-range. In this paper we focus on the study of the critical behaviour of spin systems with weak-long range couplings using renormalization group, and we review their remarkable properties. For the sake of clarity and self-consistency, we start from the classical $O(N)$ spin models and we then move to quantum spin systems.
- arXiv:1909.07337 (replaced) [pdf, ps, other]
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Title: Advantages of $q$-logarithm representation over $q$-exponential representation from the sense of scale and shift on nonlinear systemsComments: 13 pages, 3 figuresJournal-ref: Eur. Phys. J. Special Topics, vol.229, pp.773--785 (2020)Subjects: Mathematical Physics (math-ph); Statistical Mechanics (cond-mat.stat-mech)
Addition and subtraction of observed values can be computed under the obvious and implicit assumption that the scale unit of measurement should be the same for all arguments, which is valid even for any nonlinear systems. This paper starts with the distinction between exponential and non-exponential family in the sense of the scale unit of measurement. In the simplest nonlinear model ${dy}/{dx}=y^{q}$, it is shown how typical effects such as rescaling and shift emerge in the nonlinear systems and affect observed data. Based on the present results, the two representations, namely the $q$-exponential and the $q$-logarithm ones, are proposed. The former is for rescaling, the latter for unified understanding with a fixed scale unit. As applications of these representations, the corresponding entropy and the general probability expression for unified understanding with a fixed scale unit are presented. For the theoretical study of nonlinear systems, $q$-logarithm representation is shown to have significant advantages over $q$-exponential representation.
- arXiv:1909.09008 (replaced) [pdf]
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Title: Formation of a Te-Ag Honeycomb Alloy: A New Type of Two-Dimensional MaterialComments: 7 pages, 3 figures and 2 figures in supplementaryJournal-ref: J. Phys. Chem. Lett. 11, 1609 (2020)Subjects: Materials Science (cond-mat.mtrl-sci)
Inspired by the unique properties of graphene, the focus in the literature is now on investigations of various two-dimensional (2D) materials with the aim to explore their properties for future applications. The group IV analogues of graphene, i.e., silicene, germanene and stanene have been intensively studied in recent years. However, their semi-metallic band structures hamper their use in electronic applications. Hence, the synthesis of 2D materials with band gaps of various sizes has attracted a large interest. Here, we report a successful preparation of a 2D Te-Ag binary alloy with a honeycomb structure. Angle-resolved photoelectron spectroscopy (ARPES) in combination with first-principles calculations using density functional theory (DFT) confirmed the formation of this binary alloy. The semiconducting property is verified by the ARPES data and a direct gap of ~0.7 eV is predicted by the DFT calculations.
- arXiv:1909.09830 (replaced) [pdf, other]
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Title: d-SEAMS: Deferred Structural Elucidation Analysis for Molecular SimulationsComments: At this https URL 2 documents submitted: Main - 14 pages, 52 references, 10 figures Supplementary - 8 pages, 12 references, 3 figuresJournal-ref: Goswami, R., Goswami, A., & Singh, J. K. (2020). d-SEAMS: Deferred Structural Elucidation Analysis for Molecular Simulations. Journal of Chemical Information and Modeling. https://doi.org/10.1021/acs.jcim.0c00031Subjects: Computational Physics (physics.comp-ph); Materials Science (cond-mat.mtrl-sci); Atomic and Molecular Clusters (physics.atm-clus); Chemical Physics (physics.chem-ph)
Structural analyses are an integral part of computational research on nucleation and supercooled water, whose accuracy and efficiency can impact the validity and feasibility of such studies. The underlying molecular mechanisms of these often elusive and computationally expensive processes can be inferred from the evolution of ice-like structures, determined using appropriate structural analysis techniques. We present d-SEAMS, a free and open-source post-processing engine for the analysis of molecular dynamics trajectories, which is specifically able to qualitatively classify ice structures, in both strong confinement and bulk systems. For the first time, recent algorithms for confined ice structure determination have been implemented, along with topological network criteria for bulk ice structure determination. Recognizing the need for customization in structural analysis, d-SEAMS has a unique code architecture, built with `nix`, employing a `YAML`-`Lua` scripting pipeline. The software has been designed to be user-friendly and easy to extend. The engine outputs are compatible with popular graphics software suites, allowing for immediate visual insights into the systems studied. We demonstrate the features of d-SEAMS by using it to analyze nucleation in the bulk regime and for quasi-one and quasi-two-dimensional systems. Structural time evolution and quantitative metrics are determined for heterogenous ice nucleation on a silver-exposed $\beta$-AgI surface, homogenous ice nucleation, flat monolayer square ice formation and freezing of an ice nanotube.
- arXiv:1910.00771 (replaced) [pdf]
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Title: Resonantly driven singlet-triplet spin qubit in siliconComments: 12 pages, 4 figuresJournal-ref: Phys. Rev. Lett. 124, 117701 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We report implementation of a resonantly driven singlet-triplet spin qubit in silicon. The qubit is defined by the two-electron anti-parallel spin states and universal quantum control is provided through a resonant drive of the exchange interaction at the qubit frequency. The qubit exhibits long $T_2^*$ exceeding 1 $\mu$s that is limited by dephasing due to the $^{29}$Si nuclei rather than charge noise thanks to the symmetric operation and a large micro-magnet Zeeman field gradient. The randomized benchmarking shows 99.6 % single gate fidelity which is the highest reported for singlet-triplet qubits.
- arXiv:1910.02456 (replaced) [pdf, ps, other]
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Title: Ground-State Phase Diagram of an Anisotropic S=1 Ferromagnetic-Antiferromagnetic Bond-Alternating ChainComments: to be published in JPS Conf. SerSubjects: Strongly Correlated Electrons (cond-mat.str-el)
By using mainly numerical methods, we investigate the ground-state phase diagram (GSPD) of an $S=1$ ferromagnetic-antiferromagnetic bond-alternating chain with the $XXZ$ and the on-site anisotropies. This system can be mapped onto an anisotropic spin-2 chain when the ferromagnetic interaction is much stronger than the antiferromagnetic interaction. Since there are many quantum parameters in this system, we numerically obtained the GSPD on the plane of the magnitude of the antiferromagnetic coupling versus its $XXZ$ anisotropy, by use of the exact diagonalization, the level spectroscopy as well as the phenomenological renormalization group. The obtained GSPD consists of six phases. They are the $XY$1, the large-$D$ (LD), the intermediate-$D$ (ID), the Haldane (H), the spin-1 singlet dimer (SD), and the N\'eel phases. Among them, the LD, the H, and the SD phases are the trivial phases, while the ID phase is the symmetry-protected topological phase. The former three are smoothly connected without any quantum phase transitions. It is also emphasized that the ID phase appears in a wider region compared with the case of the GSPD of the anisotropic spin-2 chain with the $XXZ$ and the on-site anisotropies. We also compare the obtained GSPD with the result of the perturbation theory.
- arXiv:1910.02582 (replaced) [pdf, ps, other]
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Title: Spin Nematic Liquids of the $S=1$ Spin Ladder in Magnetic FieldComments: to be published in JPS Conference ProceedingsSubjects: Strongly Correlated Electrons (cond-mat.str-el)
The magnetization process of the $S=1$ spin ladder system is investigated using the numerical exact diagonalization of finite-size clusters. The field-induced spin nematic liquid phase was predicted to appear by our previous work. Several ground-state phase diagrams in the plane of the single-ion anisotropy and the external magnetic field are obtained in the present study.
- arXiv:1910.02585 (replaced) [pdf, ps, other]
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Title: Magnetization Plateau of the Distorted Diamond Spin ChainComments: to be published in JPS Conference ProceedingsSubjects: Strongly Correlated Electrons (cond-mat.str-el)
The frustrated quantum spin system on the distorted diamond chain lattice is investigated using the numerical diagonalization of finite-size clusters and the level spectroscopy analysis. In the previous work this system was revealed to exhibit the 1/3 magnetization plateau due to two different mechanisms depending on the coupling parameters, and the phase diagram at the 1/3 magnetization was obtained. In the present work it is found that the 1/3 magnetization plateau vanishes for sufficiently large $XY$-like coupling anisotropy. The phase diagram based on the level spectroscopy analysis is also presented.
- arXiv:1910.02587 (replaced) [pdf]
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Title: Quantum Phase Transition of the Twisted Spin TubeComments: to be published in JPS Conference ProceedingsSubjects: Strongly Correlated Electrons (cond-mat.str-el)
The $S=1/2$ twisted three-leg spin tube with the lattice distortion from the regular triangle to the isosceles one is investigated using the numerical diagonalization of finite-size clusters and the phenomenological renormalization group analysis. It is found that the quantum phase transition occurs from the spin gap phase to another one with respect to this lattice distortion.
- arXiv:1910.07991 (replaced) [pdf]
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Title: Magneto-dielectric Effect in Relaxor Dipolar Glassy Tb2CoMnO6 FilmComments: 19 pages, 6 figuresJournal-ref: Phys. Rev. B 101, 094426 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el)
We report magneto-dielectric properties of partially B-site ordered monoclinic Tb2CoMnO6 double perovskite thin film epitaxially grown by metalorganic aerosol deposition technique. Transmission electron microscopy and electron energy loss spectroscopy mapping shows the presence and distribution of both Co2+ and Co3+ ions in the film, evidencing a partial B-site disorder, which was further confirmed by the observation of reduced saturation magnetization at low temperatures. The ferromagnetic Curie temperature, TC=110 K, is slightly higher as compared to the bulk value (100 K) probably due to an in plane tensile strain. Remarkably, a short range ordering of spins at T*~190 K>>TC was established and assigned to the B-site disorder in the film. Two different dielectric relaxation peaks have been observed; they merge at the same temperature T* of short range spin correlations. Moreover, an unexpected high temperature dipolar relaxor-glass-like transition at T~T* was observed, at which a coupling to short range magnetic correlations results in a 4% magneto-dielectric coupling.
- arXiv:1910.10907 (replaced) [pdf, other]
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Title: Angle-resolved photoemission spectroscopy study of crystal electric field in heavy fermion compound CePt2In7Authors: Yang Luo, Chen Zhang, Qi-Yi Wu, Fan-Ying Wu, Jiao-Jiao Song, W. Xia, Yanfeng Guo, Jan Rusz, Peter M. Oppeneer, Tomasz Durakiewicz, Yin-Zou Zhao, Hao Liu, Shuang-Xing Zhu, Ya-Hua Yuan, Jun He, Shi-Yong Tan, Y. B. Huang, Zhe Sun, Yi Liu, H. Y. Liu, Yu-Xia Duan, Jian-Qiao MengComments: 6 pages, 4 figuresJournal-ref: Phys. Rev. B 101, 115129 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el); Superconductivity (cond-mat.supr-con)
The three-dimensional electronic structure and Ce 4f electrons of the heavy fermion superconductor CePt2In7 is investigated. Angle-resolved photoemission spectroscopy using variable photon energy establishes the existence of quasi-two and three dimensional Fermi surface topologies. Temperature-dependent 4d-4f on-resonance photoemission spectroscopies reveal that heavy quasiparticle bands begin to form at a temperature well above the characteristic (coherence) temperature T*. T* emergence may be closely related to crystal electric field splitting, particularly the low-lying heavy band formed by crystal electric field splitting.
- arXiv:1910.14362 (replaced) [pdf, other]
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Title: Optical properties of graphene quantum dots: the role of chiral symmetryJournal-ref: 2D Materials 7 (2020) 025041Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci)
We analyse the electronic and optical properties of graphene quantum dots (GQD) using accurate \textit{ab initio} many-body $GW$ and Bethe-Salpeter calculations. We show that most pristine GQD, including structures with irregular shapes, are characterized by dark low energy singlet excitations that quench fluorescence. We rationalizqe this property by exploiting the chiral symmetry of the low energy electronic states in graphene. Edge \textit{sp}$^3$ functionalization is shown to efficiently brighten these low lying excitations by distorting the \textit{sp}$^2$ backbone planar symmetry. Such findings reveal an original indirect scenario for the influence of functionalization on the photoluminescence properties.
- arXiv:1911.00342 (replaced) [pdf, other]
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Title: Microscopic model of stacking-fault potential and exciton wave function in GaAsAuthors: Mikhail V. Durnev, Mikhail M. Glazov, Xiayu Linpeng, Maria L. K. Viitaniemi, Bethany Matthews, Steven R. Spurgeon, P.V. Sushko, Andreas D. Wieck, Arne Ludwig, Kai-Mei C. FuComments: 12 pages, 10 figuresJournal-ref: Phys. Rev. B 101, 125420 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci)
Two-dimensional stacking fault defects embedded in a bulk crystal can provide a homogeneous trapping potential for carriers and excitons. Here we utilize state-of-the-art structural imaging coupled with density functional and effective-mass theory to build a microscopic model of the stacking-fault exciton. The diamagnetic shift and exciton dipole moment at different magnetic fields are calculated and compared with the experimental photoluminescence of excitons bound to a single stacking fault in GaAs. The model is used to further provide insight into the properties of excitons bound to the double-well potential formed by stacking fault pairs. This microscopic exciton model can be used as an input into models which include exciton-exciton interactions to determine the excitonic phases accessible in this system.
- arXiv:1911.00890 (replaced) [pdf, other]
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Title: Mean-field inference methods for neural networksAuthors: Marylou GabriéJournal-ref: JPhysA 2020Subjects: Disordered Systems and Neural Networks (cond-mat.dis-nn); Machine Learning (cs.LG); Machine Learning (stat.ML)
Machine learning algorithms relying on deep neural networks recently allowed a great leap forward in artificial intelligence. Despite the popularity of their applications, the efficiency of these algorithms remains largely unexplained from a theoretical point of view. The mathematical description of learning problems involves very large collections of interacting random variables, difficult to handle analytically as well as numerically. This complexity is precisely the object of study of statistical physics. Its mission, originally pointed towards natural systems, is to understand how macroscopic behaviors arise from microscopic laws. Mean-field methods are one type of approximation strategy developed in this view. We review a selection of classical mean-field methods and recent progress relevant for inference in neural networks. In particular, we remind the principles of derivations of high-temperature expansions, the replica method and message passing algorithms, highlighting their equivalences and complementarities. We also provide references for past and current directions of research on neural networks relying on mean-field methods.
- arXiv:1911.02456 (replaced) [pdf, other]
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Title: Anomalous Behavior of Magnetic Susceptibility Obtained by Quench Experiments in Isolated Quantum SystemsComments: 7 pages, 2 figures and Supplemental MaterialJournal-ref: Phys. Rev. Lett. 124, 110609 (2020)Subjects: Statistical Mechanics (cond-mat.stat-mech); Quantum Physics (quant-ph)
We examine how the magnetic susceptibility obtained by the quench experiment on isolated quantum systems is related to the isothermal and adiabatic susceptibilities defined in thermodynamics. Under the conditions similar to the eigenstate thermalization hypothesis, together with some additional natural ones, we prove that for translationally invariant systems the quench susceptibility as a function of wave vector k is discontinuous at k=0. Moreover, its values at k=0 and the k to 0 limit coincide with the adiabatic and the isothermal susceptibilities, respectively. We give numerical predictions on how these particular behaviors can be observed in experiments on the XYZ spin chain with tunable parameters, and how they deviate when the conditions are not fully satisfied.
- arXiv:1911.02575 (replaced) [pdf, other]
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Title: Entanglement and classical fluctuations at finite-temperature critical pointsComments: 28 pages, 19 figuresJournal-ref: J. Stat. Mech. (2020) 033105Subjects: Statistical Mechanics (cond-mat.stat-mech); Quantum Gases (cond-mat.quant-gas); Strongly Correlated Electrons (cond-mat.str-el); High Energy Physics - Theory (hep-th)
We investigate several entanglement-related quantities at finite-temperature criticality in the three-dimensional quantum spherical model, both as a function of temperature $T$ and of the quantum parameter $g$, which measures the strength of quantum fluctuations. While the von Neumann and the R\'enyi entropies exhibit the volume-law for any $g$ and $T$, the mutual information obeys an area law. The prefactors of the volume-law and of the area-law are regular across the transition, reflecting that universal singular terms vanish at the transition. This implies that the mutual information is dominated by nonuniversal contributions. This hampers its use as a witness of criticality, at least in the spherical model. We also study the logarithmic negativity. For any value of $g,T$, the negativity exhibits an area-law. The negativity vanishes deep in the paramagnetic phase, it is larger at small temperature, and it decreases upon increasing the temperature. For any $g$, it exhibits the so-called sudden death, i.e., it is exactly zero for large enough $T$. The vanishing of the negativity defines a "death line", which we characterise analytically at small $g$. Importantly, for any finite $T$ the area-law prefactor is regular across the transition, whereas it develops a cusp-like singularity in the limit $T\to 0$. Finally, we consider the single-particle entanglement and negativity spectra. The vast majority of the levels are regular across the transition. Only the larger ones exhibit singularities. These are related to the presence of a zero mode, which reflects the symmetry breaking. This implies the presence of sub-leading singular terms in the entanglement entropies. Interestingly, since the larger levels do not contribute to the negativity, sub-leading singular corrections are expected to be suppressed for the negativity.
- arXiv:1911.06539 (replaced) [pdf, ps, other]
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Title: Quantum Phase Transitions of the Distorted Diamond Spin ChainComments: to be published in JPS Conf. SerSubjects: Strongly Correlated Electrons (cond-mat.str-el)
The frustrated quantum spin system on the distorted diamond chain lattice suitable for the alumoklyuchevskite is investigated using the numerical diagonalization of finite-size clusters and the level spectroscopy analysis. It is found that this model exhibits three quantum phases; the ferrimagnetic phase, the spin gap one, and the gapless Tomonaga-Luttinger liquid depending on the exchange coupling parameters. The ground state phase diagram is presented.
- arXiv:1911.10264 (replaced) [pdf, other]
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Title: Orbital Tuning of Tunnel Coupling in InAs/InP Nanowire Quantum DotsAuthors: Zahra Sadre Momtaz, Stefano Servino, Valeria Demontis, Valentina Zannier, Daniele Ercolani, Francesca Rossi, Francesco Rossella, Lucia Sorba, Fabio Beltram, Stefano RoddaroComments: 7 pages, 5 figures, plus SIJournal-ref: Nano Lett. 2020, 20, 3, 1693-1699Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We report results on the control of barrier transparency in InAs/InP nanowire quantum dots via the electrostatic control of the device electron states. Recent works demonstrated that barrier transparency in this class of devices displays a general trend just depending on the total orbital energy of the trapped electrons. We show that a qualitatively different regime is observed at relatively low filling numbers, where tunneling rates are rather controlled by the axial configuration of the electron orbital. Transmission rates versus filling are further modified by acting on the radial configuration of the orbitals by means of electrostatic gating, and the barrier transparency for the various orbitals is found to evolve as expected from numerical simulations. The possibility to exploit this mechanism to achieve a controlled continuous tuning of the tunneling rate of an individual Coulomb blockade resonance is discussed.
- arXiv:1911.10366 (replaced) [pdf, other]
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Title: LDA+DMFT approach to resonant inelastic x-ray scattering in correlated materialsJournal-ref: Phys. Rev. B 101, 115130 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el); Materials Science (cond-mat.mtrl-sci)
We present a computational study of $L$-edge resonant inelastic x-ray scattering (RIXS) in correlated 3$d$ transition-metal oxides using an $ab$ $initio$ method based on local density approximation + dynamical mean-field theory (DMFT). The present method, building on Anderson impurity model with an optimized continuum bath within DMFT, is an extension of the cluster model to include unbound electron-hole pair excitations as well as material-specific charge-transfer excitations with less empirical parameters. We find a good agreement with available experimental data. The relationship between correlated bands and fluorescence-like feature in the RIXS spectra is discussed.
- arXiv:1911.10858 (replaced) [pdf, other]
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Title: Physicist's approach to public transportation networks: between data processing and statistical physicsComments: 18 pages, 9 figures, submitted to the Festschrift devoted to Prof.Dr. Jurij Kozicki on the occasion of his 70th birthdayJournal-ref: Annales UMCS A vol. LXXIV (2019) pp. 65-82Subjects: Physics and Society (physics.soc-ph); Statistical Mechanics (cond-mat.stat-mech)
In this paper we aim to demonstrate how physical perspective enriches usual statistical analysis when dealing with a complex system of many interacting agents of non-physical origin. To this end, we discuss analysis of urban public transportation networks viewed as complex systems. In such studies, a multi-disciplinary approach is applied by integrating methods in both data processing and statistical physics to investigate the correlation between public transportation network topological features and their operational stability. The studies incorporate concepts of coarse graining and clusterization, universality and scaling, stability and percolation behavior, diffusion and fractal analysis.
- arXiv:1911.12180 (replaced) [pdf, other]
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Title: How spin-orbital entanglement depends on the spin-orbit coupling in a Mott insulatorAuthors: Dorota Gotfryd, Ekaterina M. Paerschke, Jiri Chaloupka, Andrzej M. Oles, Krzysztof WohlfeldComments: 16 pages, 8 figures; accepted in Physical Review ResearchJournal-ref: Phys. Rev. Research 2, 013353 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el)
The concept of the entanglement between spin and orbital degrees of freedom plays a crucial role in understanding various phases and exotic ground states in a broad class of materials, including orbitally ordered materials and spin liquids. We investigate how the spin-orbital entanglement in a Mott insulator depends on the value of the spin-orbit coupling of the relativistic origin. To this end, we numerically diagonalize a 1D spin-orbital model with the 'Kugel-Khomskii' exchange interactions between spins and orbitals on different sites supplemented by the on-site spin-orbit coupling. In the regime of small spin-orbit coupling w.r.t. the spin-orbital exchange, the ground state to a large extent resembles the one obtained in the limit of vanishing spin-orbit coupling. On the other hand, for large spin-orbit coupling the ground state can, depending on the model parameters, either still show negligible spin-orbital entanglement, or can evolve to a highly spin-orbitally entangled phase with completely distinct properties that are described by an effective XXZ model. The presented results suggest that: (i) the spin-orbital entanglement may be induced by large on-site spin-orbit coupling, as found in the 5d transition metal oxides, such as the iridates; (ii) for Mott insulators with weak spin-orbit coupling of Ising-type, such as e.g. the alkali hyperoxides, the effects of the spin-orbit coupling on the ground state can, in the first order of perturbation theory, be neglected.
- arXiv:1912.02603 (replaced) [pdf, ps, other]
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Title: Iron-based superconductors: tales from the nucleiComments: Review article, accepted for publication in "La Rivista del Nuovo Cimento"Journal-ref: La Rivista del Nuovo Cimento 43, 1 (2020)Subjects: Superconductivity (cond-mat.supr-con); Strongly Correlated Electrons (cond-mat.str-el)
High-temperature superconductivity in Fe-based pnictides and chalcogenides has been one of the most significant recent discoveries in condensed matter physics and has attracted remarkable attention in the last decade. These materials are characterized by a complex fermiology and, as a result, feature a wide range of electronic properties as a function of different tuning parameters such as chemical doping, temperature and pressure. Along the path towards the comprehension of the physical mechanisms underlying this rich phenomenology, NMR (nuclear magnetic resonance) and NQR (nuclear quadrupole resonance) have played a role of capital importance that we review in this work. In particular, we address how NMR has contributed to the current understanding of the main regions of the electronic phase diagram of Fe-based pnictides, that is, the -- sometimes coexisting -- antiferromagnetic spin-density wave and superconducting states. We evidence the unique capability of NMR as local-probe technique of investigating the effect of quenched disorder and chemical impurities. Then, we review the NMR signatures of low-frequency fluctuations associated with the development of electronic nematicity as well as with the motion of superconducting flux lines. Finally, we discuss recent contributions of NMR and NQR which evidence an intrinsically inhomogeneous electronic charge distribution as well as an orbitally-selective behaviour.
- arXiv:1912.03094 (replaced) [pdf, other]
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Title: Universal bottleneck for thermal relaxation in disordered metallic filmsComments: accepted in JETP LettersJournal-ref: JETP Letters 111 (2), 104 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci)
We study the heat relaxation in current biased metallic films in the regime of strong electron-phonon coupling. A thermal gradient in the direction normal to the film is predicted, with a spatial temperature profile determined by the temperature-dependent heat conduction. In the case of strong phonon scattering the heat conduction occurs predominantly via the electronic system and the profile is parabolic. This regime leads to the linear dependence of the noise temperature as a function of voltage bias, in spite of the fact that all the dimensions of the film are large compared to the electron-phonon relaxation length. This is in stark contrast to the conventional scenario of relaxation limited by the electron-phonon scattering rate. A preliminary experimental study of a 200 nm thick NbN film indicates the relevance of our model for materials used in superconducting nanowire single-photon detectors.
- arXiv:1912.04267 (replaced) [pdf, other]
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Title: Non-adiabatic effects and exciton-like states during insulator-to-metal transition in warm dense hydrogenComments: 7 pages, 4 figures, Supplemental Material (10 pages)Journal-ref: Phys. Rev. B 101, 100101 (2020)Subjects: Materials Science (cond-mat.mtrl-sci)
Transition of molecular hydrogen to atomic ionized state with increase of temperature and pressure poses still unresolved problems for experimental methods and theory. Here we analyze the dynamics of this transition and show its nonequilibrium non-adiabatic character overlooked in both interpreting experimental data and in theoretical models. The non-adiabatic mechanism explains the strong isotopic effect [Zaghoo, Husband, and Silvera, Phys. Rev. B 98, 104102 (2018)] and the large latent heat [Houtput, Tempere, and Silvera, Phys. Rev. B 100, 134106 (2019)] reported recently. We demonstrate the possibility of formation of intermediate exciton-like molecular states at heating of molecular hydrogen that can explain puzzling experimental data on reflectivity and conductivity during the insulator-to-metal transition.
- arXiv:1912.06367 (replaced) [pdf]
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Title: Strength, transformation toughening and fracture dynamics of rocksalt-structure Ti1-xAlxN (0 <= x <= 0.75) alloysJournal-ref: Phys. Rev. Materials 4, 033605 (2020)Subjects: Materials Science (cond-mat.mtrl-sci)
Ab initio-calculated ideal strength and toughness describe the upper limits for mechanical properties attainable in real systems and can, therefore, be used in selection criteria for materials design. We employ density-functional ab initio molecular dynamics (AIMD) to investigate the mechanical properties of defect-free rocksalt-structure (B1) TiN and B1 Ti1-xAlxN (x = 0.25, 0.5, 0.75) solid solutions subject to [001], [110], and [111] tensile deformation at room temperature. We determine the alloys' ideal strength and toughness, elastic responses, and ability to plastically deform up to fracture as a function of the Al content. Overall, TiN exhibits greater ideal moduli of resilience and tensile strengths than TiAlN solid solutions. Nevertheless, AIMD modelingshows that, irrespective of the strain direction, the binary compound systematically fractures by brittle cleavage at its yield point. The simulations also indicate that Ti0.5Al0.5N and Ti0.25Al0.75N solid solutions are inherently more resistant to fracture and possess much greater toughness than TiN, due to the activation of local structural transformations (primarily of B1 -> wurtzite type) beyond the elastic-response regime. In sharp contrast, TiAlN alloys with 25% Al exhibit similar brittleness as TiN. The results of this work are examples of the limitations of elasticity-based criteria for prediction of strength, brittleness, ductility, and toughness in materials able to undergo phase transitions with loading. Furthermore, comparing present and previous findings, we suggest a general principle for design of hard ceramic solid solutions that are thermodynamically inclined to dissipate extreme mechanical stresses via transformation toughening mechanisms.
- arXiv:1912.07838 (replaced) [pdf, ps, other]
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Title: Kovtun-Son-Starinets Conjecture and Effects of Mass Imbalance in the Normal State of an Ultracold Fermi Gas in the BCS-BEC Crossover RegionComments: 11 pages, 9 figuresJournal-ref: J. Phys. Soc. Jpn. 89, 044005 (2020)Subjects: Quantum Gases (cond-mat.quant-gas)
We theoretically assess the conjecture proposed by Kovtun, Son, and Starinets, stating that the ratio $\eta/s$ of the shear viscosity $\eta$ to the entropy density $s$ has the lower bound as $\eta/s\ge\hbar/(4\pi k_{\mathrm{B}})$. In the normal state of a mass-imbalanced ultracold Fermi gas, consistently including strong-coupling corrections to both $\eta$ and $s$ within the self-consistent $T$-matrix approximation, we evaluate $\eta/s$ over the entire BCS (Bardeen-Cooper-Schrieffer)-BEC (Bose-Einstein condensation) crossover region, in the presence of mass imbalance. We find that $\eta/s$ achieves the minimum value $4.5\times \hbar/(4\pi k_{\mathrm{B}})$, not at the unitarity, but slightly in the BEC regime, $(k_{\mathrm{F}}a_s)^{-1}\simeq 0.4>0$ (where $a_s$ is the $s$-wave scattering length, and $k_{\mathrm{F}}$ is the Fermi momentum). In contract to the previous expectation, we find that this lower bound is almost independent of mass imbalance: Our results predict that all the mass-balanced $^6$Li-$^6$Li and $^{40}$K-$^{40}$K mixtures and the mass-imbalanced $^{40}$K-$^{161}$Dy mixture give almost the same lower bound of $\eta/s$. We also point out that the two quantum phenomena, Pauli blocking and bound-state formation, are crucial keys for the lower bound of $\eta/s$.
- arXiv:1912.09975 (replaced) [pdf, other]
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Title: Symmetry classes, many-body zero modes, and supersymmetry in the complex Sachdev-Ye-Kitaev modelComments: 10 pages, 3 figures, accepted manuscriptJournal-ref: Phys. Rev. D 101, 066017 (2020)Subjects: High Energy Physics - Theory (hep-th); Disordered Systems and Neural Networks (cond-mat.dis-nn); Strongly Correlated Electrons (cond-mat.str-el)
The complex Sachdev-Ye-Kitaev (cSYK) model is a charge-conserving model of randomly interacting fermions. The interaction term can be chosen such that the model exhibits chiral symmetry. Then, depending on the charge sector and the number of interacting fermions, level spacing statistics suggests a fourfold categorization of the model into the three Wigner-Dyson symmetry classes. In this work, inspired by previous findings for the Majorana Sachdev-Ye-Kitaev model, we embed the symmetry classes of the cSYK model in the Altland-Zirnbauer framework and identify consequences of chiral symmetry originating from correlations across different charge sectors. In particular, we show that for an odd number of fermions, the model hosts exact many-body zero modes that can be combined into a generalized fermion that does not affect the system's energy. This fermion directly leads to quantum-mechanical supersymmetry that, unlike explicitly supersymmetric cSYK constructions, does not require fine-tuned couplings, but only chiral symmetry. Signatures of the generalized fermion, and thus supersymmetry, include the long-time plateau in time-dependent correlation functions of fermion-parity-odd observables: The plateau may take nonzero value only for certain combinations of the fermion structure of the observable and the system's symmetry class. We illustrate our findings through exact diagonalization simulations of the system's dynamics.
- arXiv:2001.10499 (replaced) [pdf, other]
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Title: Vibrational excitation mechanism in tunneling spectroscopy beyond the Franck-Condon modelAuthors: Gaël Reecht, Nils Krane, Christian Lotze, Lei Zhang, Alejandro L. Briseno, Katharina J. FrankeJournal-ref: Phys. Rev. Lett. 124, 116804 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Vibronic spectra of molecules are typically described within the Franck-Condon model. Here, we show that highly resolved vibronic spectra of large organic molecules on a single layer of MoS$_{2}$ on Au(111) show spatial variations in their intensities, which cannot be captured within this picture. We explain that vibrationally mediated perturbations of the molecular wave functions need to be included into the Franck-Condon model. Our simple model calculations reproduce the experimental spectra at arbitrary position of the STM tip over the molecule in great detail.
- arXiv:2002.01683 (replaced) [pdf]
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Title: Direct control of magnetic chirality in NdMn2O5 by external electric fieldAuthors: I.A. Zobkalo, A.N. Matveeva, A. Sazonov, S.N. Barilo, S.V. Shiryaev, B. Pedersen, V. HutanuJournal-ref: Phys. Rev. B 101, 064425 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el); Materials Science (cond-mat.mtrl-sci)
Detailed investigation of the incommensurate magnetic ordering in a single crystal of multiferroic NdMn2O5 has been performed using both non-polarized and polarized neutron diffraction techniques. Below TN = 30.5 K magnetic Bragg reflections corresponding to the non-chiral type magnetic structure with propagation vector k1 = (0.5 0 kz1) occurs. Below about 27 K a new distorted magnetic modulation with a similar vector kz2 occurs, which is attributed to the magnetization of the Nd3+ ions by the Mn-sub-lattice. Strong temperature hysteresis in the occurrence of the incommensurate magnetic phases in NdMn2O5 was observed depending on the cooling or heating history of the sample. Below about 20 K the magnetic structure became of a chiral type. From spherical neutron polarimetry measurements, the resulting low-temperature magnetic structure kz3 was approximated by the general elliptic helix. The parameters of the magnetic helix-like ellipticity and helical plane orientation in regard to the crystal structure were determined. A reorientation of the helix occurs at an intermediate temperature between 4 K and 18 K. A difference between the population of right- and left-handed chiral domains of about 0.2 was observed in the as-grown crystal when cooling without an external electric field. The magnetic chiral ratio can be changed by the application of an external electric field of a few kV/cm, revealing strong magnetoelectric coupling. A linear dependence of the magnetic chirality on the applied electric field in NdMn2O5 was found. The results are discussed within the frame of the antisymmetric super-exchange model for Dzyaloshinsky-Moria interaction.
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Wed, 25 Mar 2020
- arXiv:2003.10464 [pdf, other]
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Title: Induced Half-Metallicity and Gapless Topological Superconductivity in the CrI$_3$-Pb InterfaceComments: 9 pages, 9 figuresSubjects: Superconductivity (cond-mat.supr-con); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We study a two-dimensional heterostructure comprised of a monolayer of the magnetic insulator chromium triiodide (CrI$_3$) on a superconducting lead (Pb) substrate. Through first-principles computation and a tight-binding model, we demonstrate that charge transfer from the Pb substrate dopes the CrI$_3$ into an effective half-metal, allowing for the onset of a gapless topological superconductivity phase via the proximity effect. This phase, in which there exists a superconducting gap only in part of the Fermi surface, is shown to occur generically in 2D half-metal-superconductor heterostructures which lack two-fold in-plane rotational symmetry. However, a sufficiently large proximity-induced pairing amplitude can bring such a system into a fully-gapped topological superconducting phase. As such, these results are expected to better define the optimal 2D component materials for future proposed TSC heterostructures.
- arXiv:2003.10466 [pdf, other]
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Title: Exotic Symmetries, Duality, and Fractons in 2+1-Dimensional Quantum Field TheoryComments: 56 pages. v2: many local changes and additional referencesSubjects: Strongly Correlated Electrons (cond-mat.str-el); High Energy Physics - Theory (hep-th)
We discuss nonstandard continuum quantum field theories in 2+1 dimensions. They exhibit exotic global symmetries, a subtle spectrum of charged excitations, and dualities similar to dualities of systems in 1+1 dimensions. These continuum models represent the low-energy limits of certain known lattice systems. One key aspect of these continuum field theories is the universal and important role played by discontinuous field configurations. In two companion papers, we will present 3+1-dimensional versions of these systems. In particular, we will discuss continuum quantum field theories of some models of fractons.
- arXiv:2003.10473 [pdf, other]
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Title: Effects of Structural Distortions on the Electronic Structure of T-type Transition Metal DichalcogenidesAuthors: Daniel T. Larson, Wei Chen, Steven B. Torrisi, Jennifer Coulter, Shiang Fang, Efthimios KaxirasComments: 19 pages, 10 figures, 10 tablesSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci)
Single-layer transition metal dichalcogenides (TMDCs) can adopt two distinct structures corresponding to different coordination of the metal atoms. TMDCs adopting the T-type structure exhibit a rich and diverse set of phenomena, including charge density waves (CDW) in a $\sqrt{13}\times\sqrt{13}$ supercell pattern in TaS$_2$ and TaSe$_2$, and a possible excitonic insulating phase in TiSe$_2$. These properties make the T-TMDCs desirable components of layered heterostructure devices. In order to predict the emergent properties of combinations of different layered materials, one needs simple and accurate models for the constituent layers which can take into account potential effects of lattice mismatch, relaxation, strain, and structural distortion. Previous studies have developed ab initio tight-binding Hamiltonians for H-type TMDCs [arXiv:1709.07510]. Here we extend this work to include T-type TMDCs. We demonstrate the capabilities of our model using three example systems: a 1-dimensional sinusoidal ripple, the 2$\times$2 CDW in TiSe$_2$, and the $\sqrt{13}\times\sqrt{13}$ CDW in TaS$_2$. Using the technique of band unfolding we compare the electronic structure of the distorted crystals to the pristine band structure and find excellent agreement with direct DFT calculations, provided the magnitude of the distortions remains in the linear regime.
- arXiv:2003.10475 [pdf, other]
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Title: Exact equivalences and phase discrepancies between random matrix ensemblesComments: 40 pages, 10 figuresSubjects: Mathematical Physics (math-ph); Statistical Mechanics (cond-mat.stat-mech)
We study two types of random matrix ensembles that emerge when considering the same probability measure on partitions. One is the Meixner ensemble with a hard wall and the other are two families of unitary matrix models, with weight functions that can be interpreted as characteristic polynomial insertions. We show that the models, while having the same exact evaluation for fixed values of the parameter, may present a different phase structure. We find phase transitions of the second and third order, depending on the model. Other relationships, via direct mapping, between the unitary matrix models and continuous random matrix ensembles on the real line, of Cauchy-Romanovski type, are presented and studied both exactly and asymptotically. The case of orthogonal and symplectic groups is studied as well and related to Wronskians of Chebyshev polynomials, that we evaluate at large $N$.
- arXiv:2003.10476 [pdf, other]
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Title: The Quantum Zeno effect appears in stagesComments: 6+9 pages, 3+0 figuresSubjects: Quantum Physics (quant-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
In the quantum Zeno effect, quantum measurements can block the coherent oscillation of a two-level system by freezing its state to one of the measurement eigenstates. The effect is conventionally controlled by the measurement frequency. Here we study the development of the Zeno regime as a function of the measurement strength for continuous partial measurement. We show that the onset of the Zeno regime is marked by a cascade of transitions in the system dynamics as the measurement strength is increased. They include the appearance of a region of dynamically inaccessible states and of singularities in the steady-state probability distribution of states. These newly predicted dynamical features, which can be readily observed in current experiments, show the coexistence of fundamentally unpredictable quantum jumps with those continuously monitored and reverted in recent experiments.
- arXiv:2003.10488 [pdf, other]
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Title: Multi-Node Quantum Spin Liquids on the Honeycomb LatticeComments: 7 pages, 6 figures, 2 tablesSubjects: Strongly Correlated Electrons (cond-mat.str-el)
Recently it was realized that the zigzag magnetic order in Kitaev materials can be stabilized by small negative off-diagonal interactions called $\Gamma'$-terms. To fully understand the effect of the $\Gamma'$-interactions, we investigate the quantum $K$-$\Gamma$-$\Gamma'$ model on the honeycomb lattice using variational Monte Carlo method. Interestingly, besides the Kitaev spin liquid, two additional gapless $Z_2$ quantum spin liquids (QSLs) are found when $\Gamma'>0$. These two QSLs, which are proximate to the Kitaev spin liquid, contain 14 and 8 Majorana cones in their spinon excitation spectrum and are named PKSL14 and PKSL8 respectively. The physical properties of these nodal QSLs are studied by applying out-of-plane and in-plane magnetic fields, and the results are dependent on the number of cones. We show that the QSLs in our phase diagram are belonging to a family of multi-node quantum phases which share the same projective symmetry group but contain different number ($6n+2, n\in\mathbb Z$) of Majorana cones in their excitation spectra. Our results may provide guidance for potential experimental realization of non-Kitaev gapless QSLs in relevant materials.
- arXiv:2003.10493 [pdf, other]
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Title: Phase diagrams of the ZGB model on random networksComments: 10 pages, 8 figures, to appear on Journal of Computational ChemistrySubjects: Statistical Mechanics (cond-mat.stat-mech); Materials Science (cond-mat.mtrl-sci)
In this work, we revisited the ZGB model in order to study the behavior of its phase diagram when two well-known random networks play the role of the catalytic surfaces: the Random Geometric Graph and the Erd\"{o}s-R\'{e}nyi network. The connectivity and, therefore, the average number of neighbors of the nodes of these networks can vary according to their control parameters, the neighborhood radius $\alpha$ and the linking probability $p$, respectively. In addition, the catalytic reactions of the ZGB model are governed by the parameter $y$, the adsorption rate of carbon monoxide molecules on the catalytic surface. So, to study the phase diagrams of the model on both random networks, we carried out extensive steady-state Monte Carlo simulations in the space parameters ($y,\alpha$) and ($y,p$) and showed that the continuous phase transition is greatly affected by the topological features of the networks while the discontinuous one remains present in the diagram throughout the interval of study.
- arXiv:2003.10509 [pdf, other]
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Title: Defect dynamics in growing bacterial coloniesSubjects: Biological Physics (physics.bio-ph); Soft Condensed Matter (cond-mat.soft); Populations and Evolution (q-bio.PE)
Colonies of rod-shaped bacteria constitute a system of colloidal active matter with nematic properties. As a single initial bacterium multiplies through repeated divisions, the resulting colony quickly loses long-range orientational order, but retains locally ordered domains. At the boundaries of these domains, topological defects emerge, that themselves move around randomly as the colony grows. In both experiments and simulations, we find that these defects are created at a rate that corresponds to the exponential growth of the colony, resulting in a stable defect density. We also characterize the geometric and topological properties of bacterial colonies, from which we find that the aspect ratio of the rod-shaped particles is the main regulator of both the correlation length and the defect density. Moreover, we find that the defect dynamics are well described by a Gamma distribution, which is due to repeated divisions and subsequent re-orientations of the bacteria.
- arXiv:2003.10515 [pdf, other]
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Title: Influence of Surface Hydrophilicity and Hydration on the Rotational Relaxation of Supercooled Water on Graphene Oxide SurfacesComments: 14 pages, 9 figuresSubjects: Soft Condensed Matter (cond-mat.soft)
Hydration or interfacial water present in biomolecules and inorganic solids have been shown to exhibit a dynamical transition upon supercooling. However, an understanding of the extent of the underlying surface hydrophilicity as well as the local distribution of hydrophilic/hydrophobic patches on the dynamical transition is unexplored. Here, we use molecular dynamics simulations with a TIP4P/2005 water model to study translational and rotational relaxation dynamics of interfacial water on graphene surfaces. The purpose of this study is to investigate the influence of both surface chemistry as well as the extent of hydration on the rotational transitions of interfacial water on graphene oxide (GO) surfaces in the deeply supercooled region. We have considered three graphene-based surfaces; a GO surface with equal proportions of oxidized and pristine graphene regions in a striped topology, a fully oxidized surface and a pristine graphene surface. The dipole relaxation time of interfacial water shows a strong-to-strong, strong, and a fragile-to-strong transition on these surfaces, respectively, in the temperature range of 210-298 K. In contrast, bulk water shows a fragile-to-strong transition upon supercooling. In all these cases at high hydration, interfacial water co-exists with a thick water film with bulk-like properties. To investigate the influence of bulk water on dynamical transitions, we simulated a low hydration regime where only bound water (surface water) is present on the GO surfaces and found that the rotational relaxation of surface water on both the GO and fully oxidized surfaces show a single Arrhenius behavior. Our results indicate that not only does the local extent of surface hydrophilicity play a role in determining the energy landscape explored by the water molecules upon supercooling, but the presence of bulk water also modulates the dynamic transition.
- arXiv:2003.10530 [pdf]
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Title: Understanding the fate of corona virus transmission using a simple modelSubjects: Populations and Evolution (q-bio.PE); Other Condensed Matter (cond-mat.other)
We propose a simple model for understanding the kinetics of corona virus transmission. Our model assume spreading of corona virus can happen from one to another only, if someone without enough protection comes close contact to a person carrying the corona virus. Therefore this virus spreads on a large scale within a short time through chains of such events. Using our model we provide an estimation of the number of people affected by this virus within reasonable duration of time. We choose values of different parameters of our model by non-linear least square fit of the real time data and we predict fate of this corona virus transmission using our model.
- arXiv:2003.10569 [pdf, other]
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Title: Universal conductivity dependence of pure water polyelectrolyte solutionsSubjects: Soft Condensed Matter (cond-mat.soft)
In order to understand how live matter functions one needs to understand the interaction between polyelectrolytes. We discover a general dependence of polyelectrolyte conductivity valid in at least nine decades of polyelectrolyte concentration spanning dilute and semidilute pure water solutions. Furthermore, we showed that current state of the art theories can not explain polyelectrolyte conductivity and suggest the path in transport theories which needs to be taken in order to explain polyelectrolyte conductivity.
- arXiv:2003.10586 [pdf]
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Title: Possible signatures of mixed-parity superconductivity in doped polar SrTiO3 filmsAuthors: Timo Schumann, Luca Galletti, Hanbyeol Jeong, Kaveh Ahadi, William M. Strickland, Salva Salmani-Rezaie, Susanne StemmerJournal-ref: Physical Review B 101, 100503(R) (2020)Subjects: Superconductivity (cond-mat.supr-con); Materials Science (cond-mat.mtrl-sci)
Superconductors that possess both broken spatial inversion symmetry and spin-orbit interactions exhibit a mix of spin singlet and triplet pairing. Here, we report on measurements of the superconducting properties of electron-doped, strained SrTiO3 films. These films have an enhanced superconducting transition temperature and were previously shown to undergo a transition to a polar phase prior to becoming superconducting. We show that some films show signatures of an unusual superconducting state, such as an in-plane critical field that is higher than both the paramagnetic and orbital pair breaking limits. Moreover, nonreciprocal transport, which reflects the ratio of odd versus even pairing interactions, is observed. Together, these characteristics indicate that these films provide a tunable platform for investigations of unconventional superconductivity.
- arXiv:2003.10587 [pdf, ps, other]
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Title: Third Stable Branch and Tristability of Nuclear Spin Polarization in Single Quantum Dot SystemComments: 5 pages, 3 figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Semiconductor quantum dots provide a spin-coupled system of an electron and nuclei via enhanced hyperfine interaction. We showed that the nuclear spin polarization in single quantum dots can have three stable branches under a longitudinal magnetic field. The states were accompanied by hysteresis loops around the boundaries of each branch with a change in the excitation condition. To explain these findings, we incorporated the electron spin relaxation caused by the nuclear spin fluctuation into the previously-studied dynamic nuclear spin polarization mechanism. The model reproduces the new features of nuclear spin polarization and the associated strong reduction in the observed electron spin polarization, and can refer to the tristability of nuclear spin polarization.
- arXiv:2003.10599 [pdf, other]
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Title: Clock-line photoassociation of strongly bound dimers in a magic-wavelength latticeAuthors: Oscar Bettermann, Nelson Darkwah Oppong, Giulio Pasqualetti, Luis Riegger, Immanuel Bloch, Simon FöllingComments: 6 pages, 4 figures; Supplementary MaterialSubjects: Quantum Gases (cond-mat.quant-gas); Atomic Physics (physics.atom-ph)
We report on the direct optical production and spectroscopy of $^1\mathrm{S}_0\mbox{-}^3\mathrm{P}_0$ molecules with large binding energy using the clock transition of $^{171}\mathrm{Yb}$, and on the observation of the associated orbital Feshbach resonance near $1300\,\mathrm{G}$. We measure the magnetic field dependence of the closed-channel dimer and of the open-channel pair state energy via clock-line spectroscopy in a deep optical lattice. In addition, we show that the free-to-bound transition into the dimer can be made first-order insensitive to the trap depth by choice of the lattice wavelength. Finally, we determine the fundamental intra- and interorbital scattering lengths and probe the stability of the corresponding pair states, finding long lifetimes in both interorbital interaction channels. These results are promising both for molecular clocks and for the preparation of strongly-interacting multiorbital Fermi gases.
- arXiv:2003.10603 [pdf, other]
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Title: Where Should You Park Your Car? The $\frac{1}{2}$ RuleComments: 14 pages, 7 figures, IOP format. Version 2 for publication in JSTATSubjects: Physics and Society (physics.soc-ph); Statistical Mechanics (cond-mat.stat-mech); Probability (math.PR)
We investigate parking in a one-dimensional lot, where cars enter at a rate $\lambda$ and each attempts to park close to a target at the origin. Parked cars also depart at rate 1. An entering driver cannot see beyond the parked cars for more desirable open spots. We analyze a class of strategies in which a driver ignores open spots beyond $\tau L$, where $\tau$ is a risk threshold and $L$ is the location of the most distant parked car, and attempts to park at the first available spot encountered closer than $\tau L$. When all drivers use this strategy, the probability to park at the best available spot is maximal when $\tau=\frac{1}{2}$, and parking at the best available spot occurs with probability $\frac{1}{4}$.
- arXiv:2003.10618 [pdf, other]
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Title: Momentum dependent $d_{xz/yz}$ band splitting in LaFeAsOAuthors: S. S. Huh, Y. S. Kim, W. S. Kyung, J. K. Jung, R. Kappenberger, S. Aswartham, B. Büchner, J. M. Ok, J. S. Kim, C. Dong, J. P. Hu, S. H. Cho, D. W. Shen, J. D. Denlinger, Y. K. Kim, C. KimSubjects: Superconductivity (cond-mat.supr-con)
We performed angle-resolved photoemission spectroscopy (ARPES) studies of the electronic structure of the nematic phase in LaFeAsO. Degeneracy breaking between the dxz and dyz hole bands near the {\Gamma} and M point is observed in the nematic phase. Different temperature dependent band splitting behaviors are observed at the {\Gamma} and M points. The energy of the band splitting near the M point decreases as the temperature decreases while it has little temperature dependence near the {\Gamma} point. The nematic nature of the band shift near the M point is confirmed through a detwin experiment using a piezo device. Since a momentum dependent splitting behavior has been observed in other iron based superconductors, our observation confirms that the behavior is a universal one among iron based superconductors.
- arXiv:2003.10619 [pdf, ps, other]
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Title: Occurrence control of charged exciton for a single CdSe quantum dot at cryogenic temperatures on an optical nanofiberSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Quantum Physics (quant-ph)
We discuss photo-luminescence characteristics of CdSe core/shell quantum dots at cryogenic temperatures using a hybrid system of a single quantum dot and an optical nanofiber. The key point is to control the emission species of quantum dot to charged excitons, known as trions, which have superior characteristics to neutral excitons. We investigate the photocharging behavior for the quantum dots by varying the wavelength and intensity of irradiating laser light, and establish a method to create a permanently charged situation which lasts as long as the cryogenic temperature is maintained. The present photocharging method may open a new route to applying the CdSe quantum dots in quantum photonics, and the hybrid system of photocharged quantum-dot and optical nanofiber may readily be applicable to a fiber-in-line single-photon generator.
- arXiv:2003.10625 [pdf]
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Title: Multicolor Graphdiyne Random LasersAuthors: Xiantao Jiang, Xuemei Zhao, Wenli Bao, Rongchao Shi, Jinlai Zhao, Jianlong Kang, Xuefeng Xia, Hualong Chen, Hongbo Li, Jialiang Xu, Han ZhangComments: 19 pages, 5 figuresSubjects: Optics (physics.optics); Materials Science (cond-mat.mtrl-sci)
By breaking the restriction of mirrors, random lasers from a disordered medium have found unique applications spanning from displays, spectroscopy, biomedical treatments, to Li-Fi.Gain media in the form of two-dimension with distinct physical and chemical properties may lead to the next-generation of random lasers. Graphdiyne, a 2D graphene allotrope with intrigued carbon hybridization, atomic lattice, and optoelectronic properties, has attracted increasing attention recently. Herein, the photon emission characteristics and photo-carrier dynamics in graphdiyne are systematically studied, and the multicolor random lasers have been unprecedently realized using graphdiyne nanosheets as the gain. Considering the well bio-compatibility of graphdiyne, these results may look ahead a plethora of potential applications in the nanotechnology platform based on graphdiyne.
- arXiv:2003.10648 [pdf, other]
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Title: Robust Weyl semimetallic phase in face-centered orthogonal C6 with helical carbon chainsComments: 6 pages, 4 figuresSubjects: Materials Science (cond-mat.mtrl-sci)
The exploration of topological phases in carbon allotropes offers a fascinating avenue to realize topological devices based on carbon materials. Here, using first-principles calculations, we propose a novel metastable carbon allotrope, which possesses exotically helical carbon chains bridged by quadrangle-rings. This unique structure with sp2-sp3 bonding networks crystallizes in a noncentrosymmetric face-centered orthogonal (fco) lattice with six atoms in a unit cell, thus named fco-C6. The considerable stability of fco-C6 is confirmed by phonon spectra, elastic constants, and ab initio molecular dynamics simulations. More importantly, fco-C6 exhibits extraordinary electronic properties with the minimum number of Weyl points in a time-reversal preserved Weyl system. The symmetry arguments reveal that the Weyl points are guaranteed to lie along the high-symmetry pathes and thus well separated in momentum space, exhibiting the robustness of topologically protected features. We investigate the topological surface states of fco-C6 projected on a semi-infinite (010) surface. There are only nontrivial Fermi arcs across the Fermi surface, which facilitates their measurements in experiments and further applications in carbon allotropes.
- arXiv:2003.10651 [pdf, other]
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Title: A spiking neuron constructed by the skyrmion-based spin torque nano-oscillatorComments: 5 pages, 5 figuresJournal-ref: Appl. Phys. Lett. 116, 122402 (2020)Subjects: Applied Physics (physics.app-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Magnetic skyrmions are particle-like topological spin configurations, which can carry binary information and thus are promising building blocks for future spintronic devices. In this work, we investigate the relationship between the skyrmion dynamics and the characteristics of injected current in a skyrmion-based spin torque nano-oscillator, where the excitation source is introduced from a point nano-contact at the center of the nanodisk. It is found that the skyrmion will move away from the center of the nanodisk if it is driven by a spin-polarized current; however, it will return to the initial position in the absence of stimulus. Therefore, we propose a skyrmion-based artificial spiking neuron, which can effectively implement the leaky-integrate-fire operation. We study the feasibility of the skyrmion-based spiking neuron by using micromagnetic simulations. Our results may provide useful guidelines for building future magnetic neural networks with ultra-high density and ultra-low energy consumption.
- arXiv:2003.10666 [pdf, other]
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Title: Nonequilibrium reservoir engineering of a biased coherent conductor for hybrid energy transport in nanojunctionsSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We show that a current-carrying coherent electron conductor can be treated as effective bosonic energy reservoir involving different types of electron-hole pair excitation. For weak electron-boson coupling, hybrid energy transport between nonequilibrium electrons and bosons can be described by a Landauer-like formula. This allows for unified account of a variety of heat transport problems in hybrid electron-boson systems. As applications, we study the non-reciprocal heat transport between electrons and bosons, thermoelectric current from a cold-spot and electronic cooling of the bosons. Our unified framework provides an intuitive way of understanding hybrid energy transport between electrons and bosons. It opens the way of nonequilibrium reservoir engineering for efficient energy control between different quasi-particles in the nanoscale.
- arXiv:2003.10668 [pdf, other]
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Title: Studying viral populations with tools from quantum spin chainsSubjects: Statistical Mechanics (cond-mat.stat-mech); Biological Physics (physics.bio-ph)
We study Eigen's model of quasi-species, characterized by sequences that replicate with a specified fitness and mutate independently at single sites. The evolution of the population vector in time is then closely related to that of quantum spins in imaginary time. We employ multiple perspectives and tools from interacting quantum systems to examine growth and collapse of realistic viral populations, specifically certain HIV proteins. All approaches used, including the simplest perturbation theory, give consistent results.
- arXiv:2003.10669 [pdf]
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Title: Statistics of geometric clusters in Potts model: statistical mechanics approachAuthors: P. N. TimoninComments: 14 pages, 4 figures, text rearrangedSubjects: Statistical Mechanics (cond-mat.stat-mech)
The percolation of Potts spins with equal values in Potts model on graphs (networks) is considered. The general method for finding the Potts clusters size distributions is developed. It allows for full description of percolation transition when giant cluster of equal-valued Potts spins appears. The method is applied to the short-ranged q-state ferromagnetic Potts model on the Bethe lattices with the arbitrary coordination number z. The analytical results for the field-temperature percolation phase diagram of geometric spin clusters and their size distribution are obtained. The last appears to be proportional to that of the classical non-correlated bond percolation with the bond probability, which depends on temperature and Potts model parameters.
- arXiv:2003.10671 [pdf, other]
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Title: First-principles study on the bulk and two-dimensional structures of AMnBi(A =K, Rb, Cs)-family materialsAuthors: Ziming Zhu, Chunyan Liao, Si Li, Xiaoming Zhang, Weikang Wu, Zhi-Ming Yu, Rui Yu, Wei Zhang, Shengyuan A. YangSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Magnetic materials with high mobilities are intriguing subject of research from both fundamental and application perspectives. Based on first-principle calculations, we investigate the physical properties of the already synthesized AMnBi(A =K, Rb, Cs)-family materials. We show that these materials are antiferromagnetic (AFM), with Neel temperatures above 300 K. They contain AFM ordered Mn layers, while the interlayer coupling changes from ferromagnetic (FM) for KMnBi to AFM for RbMnBi and CsMnBi. We find that these materials are narrow gap semiconductors. Owing to the small effective mass, the electron carrier mobility can be very high, reaching up to 100,000 cm2/(Vs) for KMnBi. In contrast, the hole mobility is much suppressed, typically lower by two orders of magnitude. We further study their two-dimensional (2D) single layer structures, which are found be AFM with fairly high mobility (1000 cm2/(Vs)). Their Neel temperatures can still reach room temperature. Interesting, we find that the magnetic phase transition is also accompanied by a metal-insulator phase transition, with the paramagnetic metal phase possessing a pair of nonsymmorphic-symmetry-protected 2D spin-orbit Dirac points. Furthermore, the magnetism can be effectively controlled by the applied strain. When the magnetic ordering is turned into FM, the system can become a quantum anomalous Hall insulator with gapless chiral edge states.
- arXiv:2003.10677 [pdf]
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Title: Characteristic Lengths of Interlayer Charge-Transfer in Correlated Oxide HeterostructuresAuthors: Ganesh Ji Omar, Mengsha Li, Xiao Chi, Zhen Huang, Zhi Shiuh Lim, Saurav Prakash, Shengwei Zeng, Changjian Li, Xiaojiang Yu, Chunhua Tang, Dongsheng Song, Andrivo Rusydi, Thirumalai Venkatesan, Stephen John Pennycook, Ariando AriandoComments: 40 Pages, 14 Figures, 1 TableJournal-ref: Nano Lett. 2020, 20, 4, 2493-2499Subjects: Materials Science (cond-mat.mtrl-sci); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Strongly Correlated Electrons (cond-mat.str-el)
Using interlayer interaction to control functional heterostructures with atomic-scale designs has become one of the most effective interface-engineering strategies nowadays. Here, we demonstrate the effect of a crystalline LaFeO3 buffer layer on amorphous and crystalline LaAlO3/SrTiO3 heterostructures. The LaFeO3 buffer layer acts as an energetically favored electron acceptor in both LaAlO3/SrTiO3 systems, resulting in modulation of interfacial carrier density and hence metal-to-insulator transition. For amorphous and crystalline LaAlO3/SrTiO3 heterostructures, the metal-to-insulator transition is found when the LaFeO3 layer thickness crosses 3 and 6 unit cells, respectively. Such different critical LaFeO3 thicknesses are explained in terms of distinct characteristic lengths of the redox-reaction-mediated and polar-catastrophe-dominated charge transfer, controlled by the interfacial atomic contact and Thomas-Fermi screening effect, respectively. Our results not only shed light on the complex interlayer charge transfer across oxide heterostructures but also provides a new route to precisely tailor the charge-transfer process at a functional interface.
- arXiv:2003.10679 [pdf, other]
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Title: Dark-dark soliton breathing patterns in multi-component Bose-Einstein condensatesComments: 14 pages, 12 figuresSubjects: Quantum Gases (cond-mat.quant-gas); Pattern Formation and Solitons (nlin.PS)
In this work, we explore systematically various SO(2)-rotation-induced multiple dark-dark soliton breathing patterns obtained from stationary and spectrally stable multiple dark-bright and dark-dark waveforms in trapped one-dimensional, two-component atomic Bose-Einstein condensates (BECs). The stationary states stem from the associated linear limits (as the eigenfunctions of the quantum harmonic oscillator problem) and are parametrically continued to the nonlinear regimes by varying the respective chemical potentials, i.e., from the low-density linear limits to the high-density Thomas-Fermi regimes. We perform a Bogolyubov-de Gennes (BdG) spectral stability analysis to identify stable parametric regimes of these states. Upon SO(2)-rotation, the stable steady-states, one-, two-, three-, four-, and many dark-dark soliton breathing patterns are observed in the numerical simulations. Furthermore, analytic solutions up to three dark-bright solitons in the homogeneous setting, and three-component systems are also investigated.
- arXiv:2003.10697 [pdf, ps, other]
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Title: $^{31}$P NMR studies of an iron-based superconductor Ba$_{0.5}$Sr$_{0.5}$Fe$_{2}$(As$_{1-x}$P$_{x}$)$_{2}$ with $T_\mathrm{c}$ = 29 KComments: 8 pages, 6 figures, accepted for publication in Journal of Physics: Conf. Series 2020Subjects: Superconductivity (cond-mat.supr-con); Strongly Correlated Electrons (cond-mat.str-el)
We report $^{31}$P NMR studies of an oriented polycrystalline superconductor of Ba$_{0.5}$Sr$_{0.5}$Fe$_{2}$(As$_{1-x}$P$_{x}$)$_{2}$ with $x\sim$ 0.4 ($T_\mathrm{c}$ = 29 K) at $T$ = 14$-$325 K and $B_{0}$ = 1 and 5 T. The $^{31}$P Knight shift $K_{ab}$ at $B_{0}\perp c$ shows a nearly $T$-independent uniform spin susceptibility above $T_\mathrm{c}$ and a spin singlet decrease below $T_\mathrm{c}$. The $^{31}$P nuclear spin-lattice relaxation rate 1/$T_{1}$ shows an asymptotic behavior of $a+bT$ ($a$ and $b$ are constants) at $T >$ 100 K and the minimum at 40 K with an upturn toward $T_\mathrm{c}$. The $a$ term in 1/$T_{1}$ indicates the presence of two-dimensional antiferromagnetic spin fluctuations. The negative $\theta$ = $-$15 K of the Curie-Weiss-type antiferromagnetic spin susceptibility $\chi$($Q$) $\propto$ 1/($T$+$\theta$) in the analysis of 1/$T_{1}T$ suggests antiferromagnetic instability in the superconducting state. Discussions are made from the self-consistent renormalization (SCR) theory for the spin fluctuations with interlayer correlation.
- arXiv:2003.10711 [pdf, ps, other]
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Title: Scaling of local persistence in the disordered contact processComments: 10 pages, 7 figuresSubjects: Statistical Mechanics (cond-mat.stat-mech); Disordered Systems and Neural Networks (cond-mat.dis-nn)
We study the time-dependence of the local persistence probability during a non-stationary time evolution in the disordered contact process in $d=1,2$, and $3$ dimensions. We present a method for calculating the persistence with the strong-disorder renormalization group (SDRG) technique, which we then apply in the critical point analytically for $d=1$ and numerically for $d=2,3$. According to the results, the average persistence decays at late times as an inverse power of the logarithm of time, with a universal, dimension-dependent generalized exponent. For $d=1$, the distribution of sample-dependent local persistences is shown to be characterized by a universal limit distribution of effective persistence exponents. By a phenomenological approach of rare-region effects in the active phase, we obtain a non-universal algebraic decay of the average persistence for $d=1$, and enhanced power laws for $d>1$. As an exception, for randomly diluted lattices, the algebraic decay holds to be valid for $d>1$, which is explained by the contribution of dangling ends. Results on the time-dependence of average persistence are confirmed by Monte Carlo simulations. We also prove the equivalence of the persistence with a return probability, a valuable tool for the argumentations.
- arXiv:2003.10714 [pdf, ps, other]
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Title: Analytical canonical partition function of a quasi-one dimensional system of hard disksAuthors: V.M. PergamenshchikComments: 6 pages, 4 figuresSubjects: Soft Condensed Matter (cond-mat.soft); Statistical Mechanics (cond-mat.stat-mech)
The exact canonical partition function of a hard disk system in a narrow quasi-one dimensional pore of given length and width is derived analytically in the thermodynamic limit. As a result the many body problem is reduced to solving two transcendental equations which can be easily done numerically. The longitudinal and transverse pressures in the whole density range are presented for three different pore widths. The transition from the solidlike zigzag to the liquidlike state is found to be quite sharp in the density scale but shows no genuine singularity. This transition is quantitatively described by the distribution of zigzag's windows through which disks exchange their positions across the pore.
- arXiv:2003.10716 [pdf, other]
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Title: Shear jamming and shear melting in mechanically trained frictionless particlesComments: 10 pages, 9 figuresSubjects: Soft Condensed Matter (cond-mat.soft); Disordered Systems and Neural Networks (cond-mat.dis-nn)
We investigate criticality near the jamming transition in both quiescent systems and those under shear by considering the effect of mechanical training on the jamming transition and nonlinear rheology. We simulate frictionless soft particles undergoing athermal quasi-static shear using initial configurations trained with athermal quasi-static cyclic volume deformations. The jamming transition density of the initial configuration $\varphi_{\rm J0}$ is systematically altered by tuning the ``depth'' of mechanical training. We exert a steady shear on these configurations and observe either shear jamming (gain of stiffness due to shear) or shear melting (loss of stiffness due to shear), depending on the depth of training and proximity to the jamming transition density. We also observe that the characteristic strains, at which shear jamming or melting occur, diverge at a unique density $\varphi_{\rm JS}$. This is due to the shift of the jamming transition density from $\varphi_{\rm J0}$ to $\varphi_{\rm JS}$ under shear, associated with loss of memory of the initial configuration. Finally, we thoroughly investigate nonlinear rheology near the jamming transition density, and contrary to previous works, we find a nonlinear ``softening'' takes place below as well as above the jamming transition density.
- arXiv:2003.10717 [pdf, other]
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Title: Area-Law Study of Quantum Spin System on Hyperbolic Lattice GeometriesAuthors: Andrej GendiarComments: accepted in Acta Phys. Pol. A (2020)Subjects: Statistical Mechanics (cond-mat.stat-mech); General Relativity and Quantum Cosmology (gr-qc); Quantum Physics (quant-ph)
Magnetic properties of the transverse-field Ising model on curved (hyperbolic) lattices are studied by a tensor product variational formulation that we have generalized for this purpose. First, we identify the quantum phase transition for each hyperbolic lattice by calculating the magnetization. We study the entanglement entropy at the phase transition in order to analyze the correlations of various subsystems located at the center with the rest of the lattice. We confirm that the entanglement entropy satisfies the area law at the phase transition for fixed coordination number, i.e., it scales linearly with the increasing size of the subsystems. On the other hand, the entanglement entropy decreases as power-law with respect to the increasing coordination number.
- arXiv:2003.10718 [pdf, other]
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Title: Entanglement-entropy study of phase transitions in six-state clock modelComments: accepted in Acta Phys. Pol. ASubjects: Statistical Mechanics (cond-mat.stat-mech)
The Berezinskii-Kosterlitz-Thouless (BKT) transitions of the six-state clock model on the square lattice are investigated by means of the corner-transfer matrix renormalization group method. A classical analog of the entanglement entropy $S( L, T )$ is calculated for $L \times L$ square system up to $L = 129$, as a function of temperature $T$. The entropy exhibits a peak at $T = T^*_{~}( L )$, where the temperature depends on both $L$ and the boundary conditions. Applying the finite-size scaling to $T^*_{~}( L )$ and assuming presence of the BKT transitions, the two distinct phase-transition temperatures are estimated to be $T_1^{~} = 0.70$ and $T_2^{~} = 0.88$. The results are in agreement with earlier studies. It should be noted that no thermodynamic functions have been used in this study.
- arXiv:2003.10722 [pdf]
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Title: Theoretical correction methods for optical tweezers: Acquisition of potentials of mean forces between colloidal particles in a bulk and on a surfaceComments: 15 pages and 1 figure. In version 2, each H in Eqs. (30)-(32) has been corrected to H0. In version 3, a typographical error in Eq. (12) is correctedSubjects: Soft Condensed Matter (cond-mat.soft); Data Analysis, Statistics and Probability (physics.data-an); Optics (physics.optics)
It is known that line optical tweezers (LOT) can measure potential of mean force (PMF) between colloidal particles in the bulk. However, PMF obtained with LOT is empirically modified before showing the result of the final form in order to correct the potential rise at long distances. In the present letter, we derive theoretical correction methods for acquisition of PMF by using statistical mechanics. Using the new methods, PMF can be obtained without the empirical fitting equation. Through the new methods, external potential acting on the trapped two colloidal particles induced by LOT can also be obtained. As an additional study, we explain a method for obtaining PMF between colloidal particles on a substrate surface, in which a normal optical tweezers with a fixed focal point is used. This method can also obtain the external potential acting on the trapped two colloidal particles existing on the surface.
- arXiv:2003.10723 [pdf, ps, other]
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Title: Self-similarly corrected Pade approximants for nonlinear equationsComments: Latex file, 23 pages, 1 figureJournal-ref: Int. J. Mod. Phys. B 33 (2019) 1950353Subjects: Mathematical Physics (math-ph); Statistical Mechanics (cond-mat.stat-mech)
We consider the problem of finding approximate analytical solutions for nonlinear equations typical of physics applications. The emphasis is on the modification of the method of Pad\'e approximants that are known to provide the best approximation for the class of rational functions, but do not provide sufficient accuracy or cannot be applied at all for those nonlinear problems, whose solutions exhibit behaviour characterized by irrational functions. In order to improve the accuracy, we suggest a method of self-similarly corrected Pad\'e approximants, taking into account irrational functional behaviour. The idea of the method is in representing the sought solution as a product of two factors, one of which is given by a self-similar root approximant, responsible for irrational functional behaviour, and the other being a Pad\'e approximant corresponding to a rational function. The efficiency of the method is illustrated by constructing very accurate solutions for nonlinear differential equations. A thorough investigation is given proving that the suggested method is more accurate than the method of standard Pad\'e approximants.
- arXiv:2003.10729 [pdf, ps, other]
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Title: Field Free Mutual Synchronization of PERP-STNO Pairs Studied by the Generalized Pendulum-like ModelComments: 20 pages, 9 figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Using the local coordinate transformation, any types of two-dimentional auto-oscillators can be modeled by a forced pendulum for each stable auto-oscillatory state. This can be confirmed to be equivalent to the universal model. Based on this fact, we adopt the pendulum-like model to analytically study the mutual synchronization of a pair of perpendicular-to-plane polarizer Spin-Torque Nano-Oscillators (PERP-STNOs) by magnetic dipolar coupling, which are in electrically parallel and serial connections, respectively. In this paper, the phase diagram for synchronization as a function of current and separation, locked phase angle, locking frequency, and transient states of synchronization can be analytically predicted. Here, all of them are well evidenced by macrospin simulation.
- arXiv:2003.10741 [pdf, ps, other]
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Title: Optical signatures of phase transitions and structural modulation in elemental tellurium under pressureAuthors: Diego Rodriguez, Alexander A. Tsirlin, Tobias Biesner, Teppei Ueno, Takeshi Takahashi, Kaya Kobayashi, Martin Dressel, Ece UykurComments: 7 pages, 5 figuresJournal-ref: Phys. Rev. B 101, 174104 (2020)Subjects: Materials Science (cond-mat.mtrl-sci); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
A room-temperature infrared spectroscopy study of elemental tellurium at pressures up to 8.44 GPa in the energy range 0.015-2 eV is reported. Optical signatures of the high-pressure polymorphs are investigated and compared to the results of density-functional band-structure calculations. A Drude peak is first seen in the optical conductivity around 3.5 GPa indicating a semiconductor-to-metal transition within trigonal Te-I. A sharp increase in the Drude spectral weight and dc-conductivity around 4.3 GPa signals the transformation toward the triclinic Te-II polymorph. An absorption peak around 0.15 eV appears above 5 GPa concomitant with the gradual transformation of Te-II into the structurally similar but incommensurately modulated Te-III. Microscopically, this peak can only be reproduced within a sufficiently large commensurate approximant, suggesting the low-energy optical response as a fingerprint of the structural modulation.
- arXiv:2003.10747 [pdf]
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Title: Comment on the perspective article "Thermodynamic uncertainty relations constrain non-equilibrium fluctuations"Authors: R. Dean AstumianComments: comments on Nature Physics Perspective articleSubjects: Statistical Mechanics (cond-mat.stat-mech); Biological Physics (physics.bio-ph)
In a recent perspective article, Horowitz and Gingrich discuss thermodynamic uncertainty relations that have been derived using "stochastic thermodynamics", a theory based on a hypothesis known as local detailed balance. The authors examined the foundations of this theory in their "Box 1: A brief primer on local detailed balance and stochastic thermodynamics", where a kinetic scheme for transport of particles between two reservoirs is presented. Horowitz and Gingrich arrive at a relationship between the probability to cycle through the states in one order vs. the probability to cycle in the reverse order. This relation bears on the extremely important question of what governs directionality when a system is driven away from equilibrium by contact with multiple reservoirs that are not in equilibrium with one another. In the original version of their paper the relation given for this ratio was obviously wrong and contrary to the second law of thermodynamics. Based on our private communications and on the recent paper authored by my colleagues and myself, Horowitz and Gingrich accepted the necessity of correcting the error in their Box 1. Unfortunately, in making the correction, the authors introduced an equally serious, if less transparent, mistake, and continue to base their theory on the thermodynamically impossible idea that transitions are mediated by only one of the two reservoirs. In this comment we illustrate how the principle of microscopic reversibility reveals that the true origin of directional cycling amongst a network of states is kinetic asymmetry. This understanding is important in guiding synthesis of molecular machines and other devices designed to exploit transport or catalysis to drive non-equilibrium processes.
- arXiv:2003.10748 [pdf, other]
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Title: Quantum tomography of electrical currentsAuthors: R. Bisognin, A. Marguerite, B. Roussel, M. Kumar, C. Cabart, C. Chapdelaine, A. Mohammad-Djafari, J.-M. Berroir, E. Bocquillon, B. Plaçais, A. Cavanna, U. Gennser, Y. Jin, P. Degiovanni, G. FèveComments: Preprint version, supplementary material is available at this https URLJournal-ref: Nature Communications volume 10, Article number: 3379 (2019)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
In quantum nanoelectronics, time-dependent electrical currents are built from few elementary excitations emitted with well-defined wavefunctions. However, despite the realization of sources generating quantized numbers of excitations, and despite the development of the theoretical framework of time-dependent quantum electronics, extracting electron and hole wavefunctions from electrical currents has so far remained out of reach, both at the theoretical and experimental levels. In this work, we demonstrate a quantum tomography protocol which extracts the generated electron and hole wavefunctions and their emission probabilities from any electrical current. It combines two-particle interferometry with signal processing. Using our technique, we extract the wavefunctions generated by trains of Lorentzian pulses carrying one or two electrons. By demonstrating the synthesis and complete characterization of electronic wavefunctions in conductors, this work offers perspectives for quantum information processing with electrical currents and for investigating basic quantum physics in many-body systems.
- arXiv:2003.10759 [pdf]
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Title: Synthesis of nanodiamond reinforced silver matrix nanocomposites: microstructure and mechanical propertiesSubjects: Applied Physics (physics.app-ph); Materials Science (cond-mat.mtrl-sci)
Nanodiamond reinforced silver matrix nanocomposites with different nanodiamond content are produced from pure silver and nanodiamond powders by a combination of two severe plastic deformation methods, ball-milling and high-pressure torsion (HPT). The ball milling parameters are varied to improve the distribution of the nanodiamonds in the powder blends. An optimized processing route combining both processes has been developed to achieve a homogenous dispersion of small nanodiamond particles in a nanocrystalline silver matrix. The microstructure of these nanocomposites was characterized by scanning and transmission electron microscopy. The mechanical properties were characterized by microhardness measurements and tensile tests. An increasing amount of nanodiamonds (up to 5 wt% and 15 vol%, respectively) can raise the microhardness by up to 70 % and the tensile strength by up to 60 % of the values achieved in HPT deformed pure silver. The microhardness and tensile strength is about 5 times higher than microcrystalline pure silver.
- arXiv:2003.10763 [pdf, other]
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Title: Ultrafast and Anharmonic Rabi Oscillations between Non-Bloch-BandsComments: 14 pages, 8 figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Other Condensed Matter (cond-mat.other); Atomic Physics (physics.atom-ph); Optics (physics.optics); Quantum Physics (quant-ph)
Rabi flopping between Bloch bands induced by a weak ac resonant field is a coherent effect involving interband transitions. Here we consider the fundamental processes of emission/absorption of quanta and Rabi oscillations in non-Hermitian two-band lattices exhibiting unbalanced non-Hermitian skin effect, and unveil an unprecedented scenario of Rabi flopping. The effective dipole moment of the transition - usually considered a bulk property - is however strongly dependent on boundary conditions, being greatly enhanced with increased Rabi frequency only when open boundaries are present. As the field strength is increased, Rabi oscillations rapidly become anharmonic, and transitions cease to be vertical in the energy-momentum plane until the system enters into an unstable regime (complex quasi-energy spectrum) due to secular amplification channels. Remaining stable even in the presence of complex energies, Rabi oscillations provide a vivid illustration of how the competition between non-Hermitian, non-local and Floquet influences can result in significant enhancements of physically measurable quantities.
- arXiv:2003.10764 [pdf, ps, other]
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Title: Equation of State of Four- and Five-Dimensional Hard-Hypersphere MixturesComments: 18 pages, 8 figures; this article belongs to the Special Issue Statistical Mechanics and Thermodynamics of Liquids and CrystalsJournal-ref: Entropy 22, 469 (2020)Subjects: Soft Condensed Matter (cond-mat.soft); Statistical Mechanics (cond-mat.stat-mech); Chemical Physics (physics.chem-ph)
New proposals for the equation of state of four- and five-dimensional hard-hypersphere mixtures in terms of the equation of state of the corresponding monocomponent hard-hypersphere fluid are introduced. Such proposals (which are constructed in such a way so as to yield the exact third virial coefficient) extend, on the one hand, recent similar formulations for hard-disk and (three-dimensional) hard-sphere mixtures and, on the other hand, two of our previous proposals also linking the mixture equation of state and the one of the monocomponent fluid but unable to reproduce the exact third virial coefficient. The old and new proposals are tested by comparison with published molecular dynamics and Monte Carlo simulation results and their relative merit is evaluated
- arXiv:2003.10789 [pdf, other]
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Title: Collective Modes in Excitonic Insulators: Effects of Electron-Phonon Coupling and Signatures in Optical ResponseComments: 19 pages, 13 figuresJournal-ref: Phys. Rev. B 101, 195118 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We consider a two-band spinless model describing an excitonic insulator (EI) on the two-dimensional square lattice with anisotropic hopping parameters and electron-phonon (el-ph) coupling, inspired by the EI candidate Ta$_2$NiSe$_5$. We systematically study the nature of the collective excitations in the ordered phase which originates from the interband Coulomb interaction and the el-ph coupling. When the ordered phase is stabilized only by the Coulomb interaction (pure EI phase), its collective response exhibits a massless phase mode in addition to the amplitude mode. We show that in the BEC regime, the signal of the amplitude mode becomes less prominent and that the anisotropy in the phase mode velocities is relaxed compared to the model bandstructure. Through coupling to the lattice, the phase mode acquires a mass and the signal of the amplitude mode becomes less prominent. Importantly, character of the softening mode at the boundary between the normal semiconductor phase and the ordered phase depends on the parameter condition. In particular, we point out that even for el-ph coupling smaller than the Coulomb interaction the mode that softens to zero at the boundary can have a phonon character. We also discuss how the collective modes can be observed in the optical conductivity. Furthermore, we study the effects of nonlocal interactions on the collective modes and show the possibility of realizing a coexistence of an in-gap mode and an above-gap mode split off from the single amplitude mode in the system with the local interaction only.
- arXiv:2003.10794 [pdf, ps, other]
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Title: Anisotropic Physical Properties of the Kondo Semimetal CeCu$_{1.11}$As$_2$Authors: Lukas Cvitkovich, Diego A. Zocco, Gaku Eguchi, Monika Waas, Robert Svagera, Berthold Stöger, Rajib Mondal, Arumugam Thamizhavel, Silke PaschenComments: 6 pages, 4 figures, Proceedings of the International Conference on Strongly Correlated Electron Systems (SCES2019)Subjects: Strongly Correlated Electrons (cond-mat.str-el)
The recently proposed novel materials class called Weyl-Kondo semimetal (WKSM) is a time reversal invariant but inversion symmetry broken Kondo semimetal in which Weyl nodes are pushed to the Fermi level by the Kondo interaction. Here we explore whether CeCu$_{1+x}$As$_2$ may be a new WKSM candidate. We report on its single-crystal growth, structure determination and physical properties investigation. Previously published studies on polycrystalline samples suggest that it is indeed a Kondo semimetal, which is confirmed by our investigations on single crystals. X-ray diffraction reveals that CeCu$_{1+x}$As$_2$ crystallizes in a tetragonal centrosymmetric structure, although the inversion symmetry could still be broken locally due to partially occupied Cu sites. Chemical analysis results in an average occupation $x$ = 0.11(1). The electrical resistivity increases logarithmically with decreasing temperature, and saturates below 10 K. A Kondo temperature $T_{\mathrm{K}}$ $\approx$ 4 K is extracted from entropy, estimated from the specific heat measurements. From Hall effect experiments, a charge carrier density of $8.8 \times 10^{20}$ cm$^{-3}$ is extracted, a value characteristic of a semimetal. The magnetization shows pronounced anisotropy, with no evidence of magnetic ordering down to 0.4 K. We thus classify CeCu$_{1.11}$As$_2$ as a tetragonal Kondo semimetal with anisotropic magnetic properties, with a possibly broken inversion symmetry, thus fulfilling the necessary conditions for a WKSM state.
- arXiv:2003.10798 [pdf, other]
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Title: Deformation upon impact of a concentrated suspension dropComments: Submitted to JFMJournal-ref: J. Fluid Mech. 896 (2020) R2Subjects: Fluid Dynamics (physics.flu-dyn); Soft Condensed Matter (cond-mat.soft)
We study the impact between a plate and a drop of non-colloidal solid particles suspended in a Newtonian liquid, with a specific attention to the case when the particle volume fraction, $\phi$, is close to - or even exceeds - the critical volume fraction, $\phi_c$, at which the steady effective viscosity of the suspension diverges. We use a specific concentration protocol together with an accurate determination of $\phi$ for each drop and we measure the deformation $\beta$ for different liquid viscosities, impact velocities and particle sizes. At low volume fractions, $\beta$ is found to follow closely an effective Newtonian behavior, which we determine by documenting the low deformation limit for a highly viscous Newtonian drop and characterizing the effective shear viscosity of our suspensions. By contrast, whereas the effective Newtonian approach predicts that $\beta$ vanishes at $\phi_c$, a finite deformation is observed for $\phi>\phi_c$. This finite deformation remains controlled by the suspending liquid viscosity and increases with increasing particle size, which suggests that the dilatancy of the particle phase is a key factor of the dissipation process close to and above $\phi_c$.
- arXiv:2003.10799 [pdf, other]
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Title: Imaging the coherent propagation of collective modes in the excitonic insulator candidate Ta$_2$NiSe$_5$ at room temperatureAuthors: Paolo Andrich, Hope M. Bretscher, Yuta Murakami, Denis Golež, Benjamin Remez, Prachi Telang, Anupam Singh, Luminita Harnagea, Nigel R. Cooper, Andrew J. Millis, Philipp Werner, A. K. Sood, Akshay RaoComments: Updated citationsSubjects: Strongly Correlated Electrons (cond-mat.str-el); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Excitonic insulating (EI) materials are predicted to host a condensate of electron-hole pairs in their ground state, giving rise to collective many-body effects. Although several bulk materials have been proposed as EIs recently, a direct observation of the characteristic collective behavior is still missing. Here, we use ultrafast, spatially-resolved, pump-probe microscopy to investigate the propagation of photoinduced excitations in a proposed EI, Ta$_2$NiSe$_5$. Below the critical temperature for the EI phase (328 K), we observe the propagation, for distances of up to 1 $\mu$m, of coherent oscillatory modes in the THz range at velocities of the order of 10$^5$ m/s. We develop a theoretical framework to explain these findings and suggest that this behavior results from the hybridization of phonon modes with the phase mode of the EI. We infer that the ordered EI phase is driven predominantly by interorbital Coulomb interactions and that this system falls into the BCS-BEC crossover regime. This study provides a route for the investigation of collective properties in strongly correlated materials and paves the way for applications that can take advantage of these quantum phenomena up to room temperature.
- arXiv:2003.10805 [pdf, other]
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Title: Assessment of mechanical, thermal and surface properties of monoclinic M$_1$ and M$_3$ C$_3$S by molecular dynamicsComments: 13 pages, 7 figuresSubjects: Materials Science (cond-mat.mtrl-sci); Soft Condensed Matter (cond-mat.soft); Chemical Physics (physics.chem-ph)
Monoclinic M$_1$ and M$_3$, which are the two main forms of industrial alite, were characterized at the molecular scale. Several methods were used to compute their mechanical and thermal properties. These methods were discussed and results in good agreement with experimental measurements were found. The cleavage energies were computed and the (100) and (001) showed the lowest energies for both polymorphs. Using the Wulff construction method, equilibrium shapes were proposed, and discussed with base on previous crystallographic studies.
- arXiv:2003.10811 [pdf]
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Title: Can High-Temperature Reactions Be Described by a Minimum Energy Path Model? Steric Hindrance MattersJournal-ref: CCS Chemistry 2, 460 (2020)Subjects: Chemical Physics (physics.chem-ph); Materials Science (cond-mat.mtrl-sci); Statistical Mechanics (cond-mat.stat-mech)
High-temperature reactions widely exist in nature. However, they are difficult to be characterized either experimentally or computationally. The routinely used minimum energy path (MEP) model in computational modeling of chemical reactions is not justified to describe high-temperature reactions since high-energy structures are actively involved there. In this study, using CH4 decomposition on the Cu(111) surface as an example, we systematically compare MEP results with those obtained by explicitly sampling all relevant structures via ab initio molecular dynamics (AIMD) simulations at different temperatures. Interestingly, we find that, for reactions protected by a strong steric hindrance effect, the MEP is still effectively followed even at a temperature close to the Cu melting point. In contrast, without such a protection, the flexibility of surface Cu atoms can lead to a significant free energy barrier reduction at a high temperature. Accordingly, some conclusions about graphene growth mechanisms based on MEP calculations should be revisited. Physical insights provided by this study can deepen our understanding on high-temperature surface reactions.
- arXiv:2003.10813 [pdf, ps, other]
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Title: Single-particle excitation and density excitation in Bose-Einstein condensatesAuthors: Shohei WatabeComments: 60 pages, 27 figuresSubjects: Quantum Gases (cond-mat.quant-gas)
Strong connection between the single-particle and collective excitations stands out as one of the features of Bose-Einstein condensates (BECs). We discuss theoretically these single-particle and density excitations of BECs focusing on the exact properties of the Green's functions developed by Gavoret and Nozi\`eres. We also investigate these excitations by using the many-body theory at non-zero temperatures. First, we revisited the earlier study by Gavoret and Nozi\`eres, involving the subsequent results by Nepomnyashchii and Nepomnyashchii, in terms of the matrix formalism. This formalism is an extension of the Nambu representation for the single-particle Green's function of BECs to discuss the density and current response functions with reducing the complexity of calculations. We describe the exact low-energy properties of the correlation and vertex functions, and discuss the correspondence of the spectra between the single-particle and density excitations in the low-energy regime. After deriving the exact low-energy structures of the Green's functions, we develop a many-body approximation theory of BECs with making the use of the matrix formalism for describing the single-particle Green's function and the density response function at non-zero temperatures. We show how the peaks of the single-particle spectral function and the density response function behave with an increasing temperature. Many-body effect on the single-particle spectral function and the density response function is included within a random phase approximation, where satellite structures emerge because of beyond-mean-field effects. Brief comments are also made on recent theories casting doubt upon the conventional wisdom of the BEC: the equivalence of the dispersion relations between the single-particle and collective excitations in the low-energy and low-momentum regime.
- arXiv:2003.10814 [pdf, other]
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Title: A jamming plane of sphere packingsComments: 19 pages, 20 figuresSubjects: Soft Condensed Matter (cond-mat.soft); Disordered Systems and Neural Networks (cond-mat.dis-nn); Statistical Mechanics (cond-mat.stat-mech)
The concept of jamming has attracted great research interest due to its broad relevance in soft matter such as liquids, glasses, colloids, foams, and granular materials, and its deep connection to the sphere packing problem and optimization problems. Here we show that the domain of amorphous jammed states of frictionless spheres can be significantly extended, from the well-known jamming-point at a fixed density, to a jamming-plane that spans the density and shear strain axes. We explore the jamming-plane, via athermal and thermal simulations of compression and shear jamming, with a help of an efficient swap algorithm to prepare initial equilibrium configurations. The jamming-plane can be divided into reversible-jamming and irreversible-jamming regimes, based on the reversibility of the route from the initial configuration to jamming. Our results suggest that the irreversible-jamming behavior reflects an escape from the meta-stable glass basin to which the initial configuration belongs to, or the absence of such basins. All jammed states, either compression or shear jammed, are isostatic, and exhibit jamming criticality of the same universality class. However, the anisotropy of contact networks non-trivially depends on the jamming density and strain. Among all state points on the jamming-plane, the jamming-point is a unique one with the minimum jamming density and the maximum randomness. For lattice packings, the jamming-plane shrinks into a single shear jamming-line that is independent of initial configurations. Our study paves the way for solving the long-standing random close packing problem, and provides a more complete framework to understand jamming.
- arXiv:2003.10818 [pdf, ps, other]
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Title: Photoinduced $η$-pairing in One-dimensional Mott InsulatorsComments: 6 pages, 3 figures, contributions to SCES 2019Subjects: Strongly Correlated Electrons (cond-mat.str-el)
Employing the density-matrix renormalization group technique in the matrix-product-state representation, we investigate the photoexcited superconducting correlations induced by the $\eta$-pairing mechanism in the half-filled Hubbard chain. We estimate the characteristic pair correlation function and verify the accuracy of our numerical results by comparison with exact-diagonalization data for small systems. The optimal parameter set of the pump that most enhances the $\eta$-pair correlations, is calculated in the strong-coupling regime. For such a pump, we explore the possibility of quasi-long-range order.
- arXiv:2003.10836 [pdf, other]
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Title: Effects of Disorder on the Transport of Collective Modes in an Excitonic CondensateComments: 21 pages, 10 figures. v2: Added reference to concurrent preprintSubjects: Strongly Correlated Electrons (cond-mat.str-el); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
An excitonic insulator (EI) is an unconventional quantum phase of matter in which excitons, bound pairs of electrons and holes, undergo Bose--Einstein condensation, forming a macroscopic coherent state. While its existence was first hypothesized half a century ago, the EI has eluded experimental observation in bulk materials for decades. In the last few years, a resurgence of interest in the subject has been driven by the identification of several candidate materials suspected to support an excitonic condensate. However, one obstacle in verifying the nature of these systems has been to find signatures of the EI that distinguish it from a normal insulator. To address this, we focus on a clear qualitative difference between the two phases: the existence of Goldstone modes born by the spontaneous breaking of a $U(1)$ symmetry in the EI. Even if this mode is gapped, as occurs in the case of an approximate symmetry, this branch of collective modes remains a fundamental feature of the low-energy dynamics of the EI provided the symmetry-breaking is small. We study a simple model that realizes an excitonic condensate, and use mean field theory within the random-phase approximation to determine its collective modes. We subsequently develop a diagrammatic method to incorporate the effects of disorder perturbatively, and use it to determine the scattering rate of the collective modes. We interpret our results within an an effective field theory. The collective modes are found to be robust against symmetry-preserving disorder, implying an experimental fingerprint unique to the EI: the ballistic propagation of low-lying modes over mesoscopic distances, at electronic-scale velocities. We suggest this could affect thermal transport at low temperatures, and could be observed via spatially-resolved pump-probe spectroscopy through the coherent response of phonons that hybridize with the collective modes.
- arXiv:2003.10856 [pdf, other]
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Title: q-Weibull distributions describing commercial service routesComments: 13 pages, 8 figuresSubjects: Physics and Society (physics.soc-ph); Statistical Mechanics (cond-mat.stat-mech)
We present an investigation of the mode of road transport in Brazil combining tools of complex networks and real-data. Our analysis involves a data-set based on the service routes inscribed on the Brazilian Transport Agency database. Although connectivity distributions of road networks worldwide are usually claimed as described by a power-law fashion, we report a better fit for the Brazilian case offered by the q-Weibull distribution. In our approach nodes assume the role of localities, whereas links represent service routes among them. Interestingly, a rapid drop takes place on the tail of the data distribution for a particular range of the number of outgoing connections. The mechanism responsible for driving this drop is revealed by investigating the spectral centrality of the network and different patterns of disassortative mixture, for both incoming and outgoing distributions. Besides a discussion about a power law description, we report a contrast with two different distributions. They are interpolated by the q-Weibull one: the Weibull and the q-exponential distributions. Moreover, we study the reciprocity of this network, which reflects the influence of mutual links over dynamical processes. This kind of analysis is indispensable for studies on human mobility, shipping, and a multi-modal perspective.
- arXiv:2003.10861 [pdf, other]
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Title: Portably parallel construction of a CI wave function from a matrix-product state using the Charm++ frameworkSubjects: Computational Physics (physics.comp-ph); Strongly Correlated Electrons (cond-mat.str-el)
The constructions of configuration interaction (CI) expansions from a matrix-product state (MPS) involves numerous matrix operations and the skillful sampling of important configurations when in a huge Hilbert space. In this work, we present an efficient procedure for constructing CI expansions from MPS using the Charm++ parallel programming framework, upon which automatic load balancing and object migration facilities can be employed. This procedure was employed in the MPS-to-CI utility (Moritz et al., J. Chem. Phys. 2007, 126, 224109), sampling-reconstructed complete active space algorithm (SR-CAS, Boguslawski et al., J. Chem. Phys. 2011, 134, 224101) and entanglement-driven genetic algorithm (EDGA, Luo et al., J. Chem. Theory Comput. 2017, 13, 4699-4710). It enhances productivity and allows the sampling programs evolve to their population-expansion versions (e.g., EDGA with population expansion [PE-EDGA]). Examples of 1,2-dioxetanone and firefly dioxetanone anion (FDO-) molecules demonstrated that 1) the procedure could be flexibly employed among various multi-core architectures; 2) the parallel efficiencies could be persistently improved simply by increasing the proportion of asynchronous executions; 3) PE-EDGA could construct a CAS-type CI wave function from a huge Hilbert space, with 0.9952 CI completeness and 96.7% correlation energy via ~1.66x10^6 configurations (only 0.0000028% of the total configurations) of a bi-radical state of FDO- molecule using the full valence active space within a few hours.
- arXiv:2003.10872 [src]
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Title: Dispersion-free optical activity in non-centrosymmetric metalsAuthors: V.P.MineevComments: 6 pages, no figures. arXiv admin note: text overlap with arXiv:1903.04400 The statement about nonzero antisymmetric tensor of conductivity in noncentrosymmetric metals with point group $C_{4v}$ is wrong. The error was made in the Eq.(24) for v_{\pm}. As result, in Eq.(36) \sigma^a{xy}=0. The corresponding optical properties do not take placeSubjects: Strongly Correlated Electrons (cond-mat.str-el)
According to the Onsager principle a matrix of kinetic coefficients is symmetric in a system not violating time inversion symmetry. The antisymmetry is possible in systems with broken time inversion symmetry f.i. in systems in external magnetic field. An exception to this rule is presented here. It is shown that in a tetragonal metals with point group $C_{4v}$ not violating time inversion the conductivity tensor is antisymmetric. The corresponding optical properties are considered.
- arXiv:2003.10902 [pdf, other]
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Title: Vortex solutions of Liouville equation and quasi spherical surfacesComments: 17 pages, 15 figures;Subjects: General Relativity and Quantum Cosmology (gr-qc); Other Condensed Matter (cond-mat.other); High Energy Physics - Theory (hep-th); Mathematical Physics (math-ph)
We identify the two-dimensional surfaces corresponding to certain solutions of the Liouville equation of importance for mathematical physics, the non-topological Chern-Simons (or Jackiw-Pi) vortex solutions, characterized by an integer $N \ge 1$. Such surfaces, that we call $S^2 (N)$, have positive constant Gaussian curvature, $K$, but are spheres only when $N=1$. They have edges, and, for any fixed $K$, have maximal radius $c$ that we find here to be $c = N / \sqrt{K} $. If such surfaces are constructed in a laboratory by using graphene (or any other Dirac material), our findings could be of interest to realize table-top Dirac massless excitations on nontrivial backgrounds. We also briefly discuss the type of three-dimensional spacetimes obtained as the product $S^2 (N) \times \mathbb{R}$.
- arXiv:2003.10905 [pdf, other]
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Title: Adiabatic preparation of entangled, magnetically ordered states with cold bosons in optical latticesAuthors: Araceli Venegas-Gomez, Johannes Schachenmayer, Anton S. Buyskikh, Wolfgang Ketterle, Maria Luisa Chiofalo, Andrew J. DaleySubjects: Quantum Gases (cond-mat.quant-gas); Quantum Physics (quant-ph)
We analyze a scheme for preparation of magnetically ordered states of two-component bosonic atoms in optical lattices. We compute the dynamics during adiabatic and optimized time-dependent ramps to produce ground states of effective spin Hamiltonians, and determine the robustness to decoherence for realistic experimental system sizes and timescales. Ramping parameters near a phase transition point in both effective spin-1/2 and spin-1 models produces entangled spin-symmetric states that have potential future applications in quantum enhanced measurement. The preparation of these states and their robustness to decoherence is quantified by computing the Quantum Fisher Information of final states. We identify that the generation of useful entanglement should in general be more robust to heating than it would be implied by the state fidelity, with corresponding implications for practical applications.
- arXiv:2003.10917 [pdf, other]
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Title: Vortices with magnetic field inversion in non-centrosymmetric superconductorsComments: 10 pages, 4 figuresSubjects: Superconductivity (cond-mat.supr-con); High Energy Physics - Theory (hep-th)
Superconducting materials with non-centrosymmetric lattices lacking the space inversion symmetry exhibit a variety of interesting parity-breaking phenomena, including magneto-electric effect, spin-polarized currents, helical states, and unusual Josephson effect. We demonstrate, within a Ginzburg-Landau framework describing non-centrosymmetric superconductors with $O$ point group symmetry, that vortices can exhibit an inversion of the magnetic field at a certain distance from the vortex core. In a stark contrast to conventional superconducting vortices, the magnetic-field reversal in the parity-broken superconductor leads to non-monotonic intervortex forces and, as a consequence, to the exotic properties of the vortex matter such as the formation of vortex bound states, vortex clusters, and appearance of metastable vortex/anti-vortex bound states.
- arXiv:2003.10918 [pdf, other]
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Title: Spiral magnetic field and vortex clustering in noncentrosymmetric superconductorsComments: 10 pages, 5 figuresSubjects: Superconductivity (cond-mat.supr-con)
We study magnetic response and vortex states in noncentrosymmetric superconductors with $O$ or $T$ symmetry. We microscopically derive Ginzburg-Landau free energy, which exhibits a substantial temperature dependence. For some materials the later leads to a crossover from type-1 superconductivity at elevated temperature to vortex states at lower temperature. Next we show that magnetic field can be solved in terms of complex force free fields. Using that we uncover that magnetic field of a vortex decays in spirals. Due to that intervortex and vortex-boundary interaction becomes non-monotonic with multiple minima. This implies that vortices form bound states with other vortices, antivortices and boundary.
- arXiv:2003.10922 [pdf, ps, other]
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Title: Market structure dynamics during COVID-19 outbreakComments: 1 page, figuresSubjects: Statistical Finance (q-fin.ST); Statistical Mechanics (cond-mat.stat-mech)
In this note, we discuss the impact of the COVID-19 outbreak from the perspective of the market-structure. We observe that the US market-structure has dramatically changed during the past four weeks and that the level of change has followed the number of infected cases reported in the USA. Presently, market-structure resembles most closely the structure during the middle of the 2008 crisis but there are signs that it may be starting to evolve into a new structure altogether. This is the first article of a series where we will be analyzing and discussing market-structure as it evolves to a state of further instability or, more optimistically, stabilization and recovery.
- arXiv:2003.10929 [pdf, other]
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Title: Shear thinning and thickening in spherical nanoparticle dispersionsComments: Submitted to Phys Rev ESubjects: Soft Condensed Matter (cond-mat.soft)
We present a molecular dynamics study of the flow of rigid spherical nanoparticles in a simple fluid. We evaluate the viscosity of the dispersion as a function of shear rate and nanoparticle volume fraction. We observe shear thinning behavior at low volume fractions, as the shear rate increases, the shear forces overcome the brownian forces, resulting in more frequent and more violent collisions between the nanoparticles. This in turn results in more dissipation. We show that in order to be in the shear thinning regime the nanoparticle have to order themselves into layers longitudinal to the flow to minimize the collisions. As the nanoparticle volume fraction increases there is less room to form the ordered layers, consequently as the shear rate increases the nanoparticles collide more which results in turn in shear thickening. Most interestingly, we show that at intermediate volume fractions the system exhibits metastability, with successions of ordered and disordered states along the same trajectory. Our results suggest that for nanoparticles in a simple fluid the hydro-clustering phenomenon is not present, instead the order-disorder transition is the leading mechanism for the transition from shear thinning to shear thickening.
- arXiv:2003.10932 [pdf, other]
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Title: Microscopic model of the doping dependence of line widths in monolayer transition metal dichalcogenidesComments: 11 pages, 2 figures, submitted to JCP special issue on Two-Dimensional MaterialsSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci)
A fully microscopic model of the doping-dependent exciton and trion line widths in the absorption spectra of monolayer transition metal dichalcogenides in the low temperature and low doping regime is explored. The approach is based on perturbation theory and avoids the use of phenomenological parameters. In the low-doping regime, we find that the trion line width is relatively insensitive to doping levels while the exciton line width increases monotonically with doping. On the other hand, we argue that the trion line width shows a somewhat stronger temperature dependence. The magnitudes of the line widths are likely to be masked by phonon scattering for $T \geq 20$ K in encapsulated samples in the low doping regime. We discuss the breakdown of perturbation theory, which should occur at relatively low doping levels and low temperatures. Our work also paves the way towards understanding a variety of related scattering processes, including impact ionization and Auger scattering in clean 2D samples.
- arXiv:2003.10936 [pdf, other]
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Title: Bending moduli for thirty-two select atomic monolayers from first principlesComments: 16 pages, 2 figures, 1 tableSubjects: Materials Science (cond-mat.mtrl-sci); Applied Physics (physics.app-ph)
We calculate bending moduli along the principal directions for thirty-two select atomic monolayers using ab initio Density Functional Theory (DFT). Specifically, considering representative materials from each of Groups IV, V, III-V monolayers, transition metal dichalcogenides, Group III monochalcogenides, Group IV monochalcogenides, and transition metal trichalcogenides, we utilize the recently developed Cyclic DFT method to calculate the bending moduli in the practically relevant but previously intractable low-curvature limit. We find that the moduli generally increase with thickness of the monolayer and that structures with a rectangular lattice are prone to a higher degree of anisotropy relative to those with a honeycomb lattice. We also find that exceptions to these trends are generally a consequence of unusually strong/weak bonding and/or significant structural relxation related effects.
- arXiv:2003.10961 [pdf]
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Title: XUV Induced Bleaching of a Tin Oxo Cage Photoresist Studied by High Harmonic Absorption SpectroscopyAuthors: Najmeh Sadegh, Maarten van der Geest, Jarich Haitjema, Filippo Campi, Sonia Castellanos, Peter M. Kraus, Albert M. BrouwerComments: 8 pages, 8 figuresSubjects: Applied Physics (physics.app-ph); Materials Science (cond-mat.mtrl-sci)
Inorganic molecular materials such as tin oxo cages are a promising generation of photoresists compatible with the demands of the recently developed Extreme UltraViolet (EUV) lithography technology. Therefore, a detailed understanding of the photon-induced reactions which occur in photoresists after exposure is important. We used XUV broadband laser pulses in the range of 25-40 eV from a table-top high-harmonic source to expose thin films of the tin oxo cage resist to shed light on some of the photo-induced chemistry via XUV absorption spectroscopy. During the exposure, the transmitted spectra were recorded and a noticeable absorbance decrease was observed in the resist. Dill parameters were extracted to quantify the XUV induced conversion and compared to EUV exposure results at 92 eV. Based on the absorption changes, we estimate that approximately 60% of tin-carbon bonds are cleaved at the end of the exposure.
- arXiv:2003.10966 [pdf]
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Title: Anisotropic swelling of elastomers filled with aligned 2D materialsJournal-ref: 2D Materials, Volume 7, Number 2, Page 025031, 2020Subjects: Applied Physics (physics.app-ph); Materials Science (cond-mat.mtrl-sci); Soft Condensed Matter (cond-mat.soft)
A comprehensive study has been undertaken on the dimensional swelling of graphene-reinforced elastomers in liquids. Anisotropic swelling was observed for samples reinforced with graphene nanoplatelets (GNPs), induced by the in-plane orientation of the GNPs. Upon the addition of the GNPs, the diameter swelling ratio of the nanocomposites was significantly reduced, whereas the thickness swelling ratio increased and was even greater than that of the unfilled elastomers. The swelling phenomenon has been analyzed in terms of a modification of the Flory-Rhener theory. The newly-derived equations proposed herein, can accurately predict the dependence of dimensional swelling (diameter and thickness) on volume swelling, independent of the type of elastomer and solvent. The anisotropic swelling of the samples was also studied in combination with the evaluation of the tensile properties of the filled elastomers. A novel theory that enables the assessment of volume swelling for GNP-reinforced elastomers, based on the filler geometry and volume fraction has been developed. It was found that the swelling of rubber nanocomposites induces a biaxial constraint from the graphene flakes.
- arXiv:2003.10967 [pdf, other]
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Title: Canted antiferromagnetic order in the monoaxial chiral magnets V$_{1/3}$TaS$_2$ and V$_{1/3}$NbS$_{2}$Authors: Kannan Lu, Deepak Sapkota, Lisa DeBeer-Schmitt, Yan Wu, Huibo Cao, Norman Mannella, David Mandrus, Adam A. Aczel, Gregory J. MacDougallComments: 10 pages, 6 figuresSubjects: Materials Science (cond-mat.mtrl-sci); Strongly Correlated Electrons (cond-mat.str-el)
The Dzyaloshinskii-Moriya (DM) interaction is present in the transition metal dichalcogenides (TMDC) magnets of form $M_{1/3}T$S$_{2}$ ($M$ $=$ 3d transition metal, $T$ $\in$ {Nb, Ta}), given that the intercalants $M$ form $\sqrt{3}\times\sqrt{3}$ superlattices within the structure of the parent materials $T$S$_2$ and break the centrosymmetry. Competition between the DM and ferromagnetic exchange interactions in these systems has been shown to stabilize a topological defect known as a chiral soliton in select intercalated TMDCs, initiating interest both in terms of fundamental physics and the potential for technological applications. In the current article, we report on our study of the materials V$_{1/3}$TaS$_2$ and V$_{1/3}$NbS$_2$, using a combination of x-ray powder diffraction, magnetization and single crystal neutron diffraction. Historically identified as ferromagnets, our diffraction results instead reveal that vanadium spins in these compounds are arranged into an A-type antiferromagnetic configuration at low temperatures. Refined moments are 1.37(6)$\mu_{B}$ and 1.50(9)$\mu_{B}$ for V$_{1/3}$TaS$_2$ and V$_{1/3}$NbS$_2$, respectively. Transition temperatures $T_{c}$~$=$~32K for V$_{1/3}$TaS$_{2}$ and 50K for V$_{1/3}$NbS$_{2}$ are obtained from the magnetization and neutron diffraction results. We attribute the small net magnetization observed in the low-temperature phases to a subtle ($\sim$2$^{\circ}$) canting of XY-spins in the out-of-plane direction. These new results are indicative of dominant antiferromagnetic exchange interactions between the vanadium moments in adjacent ab-planes, likely eliminating the possibility of identifying stable chiral solitons in the current materials.
- arXiv:2003.10968 [pdf]
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Title: The incommensurate magnet iron monophosphide FeP: Crystal growth and characterizationAuthors: I. O. Chernyavskii, S. E. Nikitin, Y. A. Onykiienko, D. S. Inosov, Q. Stahl, J. Geck, X. C. Hong, C. Hess, S. Gaß, A. U. B. Wolter, D. Wolf, A. Lubk, D. V. Efremov, F. Yokaichiya, S. Aswartham, B. Büchner, I. V. MorozovSubjects: Materials Science (cond-mat.mtrl-sci)
We report an optimized chemical vapor transport method, which allows growing FeP single crystals up to 500 mg in mass and 80 $mm^{3}$ in volume. The high quality of the crystals obtained by this method was confirmed by means of EDX, high-resolution TEM, low-temperature single crystal XRD and neutron diffraction experiments. We investigated the transport and magnetic properties of the single crystals and calculated the electronic band structure of FeP. We show both theoretically and experimentally, that the ground state of FeP is metallic. The examination of the magnetic data reveals antiferromagnetic order below T$_{N}$ =119 K while transport remains metallic in both the paramagnetic and the antiferromagnetic phase. The analysis of the neutron diffraction data shows an incommensurate magnetic structure with the propagation vector Q=(0, 0, $\pm{\delta}$), where ${\delta}$ $\sim$ 0.2. For the full understanding of the magnetic state, further experiments are needed. The successful growth of large high-quality single crystals opens the opportunity for further investigations of itinerant magnets with incommensurate spin structures using a wide range of experimental tools.
- arXiv:2003.10970 [pdf, other]
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Title: Non-superconducting electronic ground state in pressurized BaFe$_2$S$_3$ and BaFe$_2$S$_{2.5}$Se$_{0.5}$Authors: Hualei Sun, Xiaodong Li, Yazhou Zhou, Jia Yu, Benjamin A. Frandsen, Shan Wu, Zhijun Xu, Sheng Jiang, Qingzhen Huang, Edith Bourret-Courchesne, Liling Sun, Jeffrey W. Lynn, Robert J. Birgeneau, Meng WangComments: 7 pages, 5 figuresJournal-ref: Phys. Rev. B 101, 205129 (2020)Subjects: Superconductivity (cond-mat.supr-con); Strongly Correlated Electrons (cond-mat.str-el)
We report a comprehensive study of the spin ladder compound BaFe$_2$S$_{2.5}$Se$_{0.5}$ using neutron diffraction, inelastic neutron scattering, high pressure synchrotron diffraction, and high pressure transport techniques. We find that BaFe$_2$S$_{2.5}$Se$_{0.5}$ possesses the same $Cmcm$ structure and stripe antiferromagnetic order as does BaFe$_2$S$_3$, but with a reduced N{\'{e}}el temperature of $T_N=98$ K compared to 120 K for the undoped system, and a slightly increased ordered moment of 1.40$\mu_B$ per iron. The low-energy spin excitations in BaFe$_2$S$_{2.5}$Se$_{0.5}$ are likewise similar to those observed in BaFe$_2$S$_{3}$. However, unlike the reports of superconductivity in BaFe$_2$S$_3$ below $T_c \sim 14$~K under pressures of 10~GPa or more, we observe no superconductivity in BaFe$_2$S$_{2.5}$Se$_{0.5}$ at any pressure up to 19.7~GPa. In contrast, the resistivity exhibits an upturn at low temperature under pressure. Furthermore, we show that additional high-quality samples of BaFe$_2$S$_3$ synthesized for this study likewise fail to become superconducting under pressure, instead displaying a similar upturn in resistivity at low temperature. These results demonstrate that microscopic, sample-specific details play an important role in determining the ultimate electronic ground state in this spin ladder system. We suggest that the upturn in resistivity at low temperature in both BaFe$_2$S$_3$ and BaFe$_2$S$_{2.5}$Se$_{0.5}$ may result from Anderson localization induced by S vacancies and random Se substitutions, enhanced by the quasi-one-dimensional ladder structure.
- arXiv:2003.10972 [pdf]
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Title: Realising biaxial reinforcement via orientation-induced anisotropic swelling in graphene-based elastomersJournal-ref: 2020,12, 3377-3386 Nanoscale, 2020, 12, 3377-3386Subjects: Applied Physics (physics.app-ph); Materials Science (cond-mat.mtrl-sci)
The biaxial mechanical properties constitute another remarkable advantage of graphene, but their evaluation has been overlooked in polymer nanocomposites. Herein, we provided an innovative and practical method to characterise biaxial reinforcement from graphene via swelling of elastomers, where graphene nanoplatelets were controlled to be oriented in-plane. The in-plane-aligned graphene imposed a biaxial constraining force to the elastomer during the swelling process that led to the anisotropic swelling behaviour of the bulk nanocomposites.
- arXiv:2003.10979 [pdf, other]
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Title: Long-wavelength density fluctuations as nucleation precursorsJournal-ref: Phys. Rev. E 101, 052122 (2020)Subjects: Statistical Mechanics (cond-mat.stat-mech); Soft Condensed Matter (cond-mat.soft); Chemical Physics (physics.chem-ph)
Recent theories of nucleation that go beyond Classical Nucleation Theory predict that diffusion-limited nucleation of both liquid droplets and of crystals from a low-density vapor (or weak solution) begins with long-wavelength density fluctuations. This means that in the early stages of nucleation, 'clusters' can have low density but large spatial extent, which is at odds with the classical picture of arbitrarily small clusters of the condensed phase. We present the results of kinetic Monte Carlo simulations using Forward Flux Sampling to show that these predictions are confirmed: namely that on average, nucleation begins in the presence of low-amplitude, but spatially extended density fluctuations thus confirming a significant prediction of the non-classical theory.
- arXiv:2003.10989 [pdf, other]
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Title: Dynamical low-noise microwave source for cold atom experimentsComments: The following article has been submitted to Review of Scientific Instruments. After it is published, it will be found at this https URL v2: Typo in the abstract correctedSubjects: Quantum Physics (quant-ph); Quantum Gases (cond-mat.quant-gas); Atomic Physics (physics.atom-ph)
The generation and manipulation of ultracold atomic ensembles in the quantum regime require the application of dynamically controllable microwave fields with ultra-low noise performance. Here, we present a low-phase-noise microwave source with two independently controllable output paths. Both paths generate frequencies in the range of $6.835\,$GHz $\pm$ $25\,$MHz for hyperfine transitions in $^{87}$Rb. The presented microwave source combines two commercially available frequency synthesizers: an ultra-low-noise oscillator at $7\,$GHz and a direct digital synthesizer for radiofrequencies. We demonstrate a low integrated phase noise of $580\,\mu$rad in the range of $10\,$Hz to $100\,$kHz and fast updates of frequency, amplitude and phase in sub-$\mu$s time scales. The highly dynamic control enables the generation of shaped pulse forms and the deployment of composite pulses to suppress the influence of various noise sources.
- arXiv:2003.10993 [pdf, other]
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Title: Emergence of generalized hydrodynamics in the non-local Luttinger modelAuthors: Per MoosaviComments: 16 pages, LaTeX; minor updatesSubjects: Statistical Mechanics (cond-mat.stat-mech); Mathematical Physics (math-ph)
We propose the Luttinger model with finite-range interactions as a simple tractable example in 1+1 dimensions to analytically study the emergence of Euler-scale hydrodynamics in a quantum many-body system. This non-local Luttinger model is an exactly solvable quantum field theory somewhere between conformal and Bethe-ansatz integrable models. Applying the recent proposal of generalized hydrodynamics, we show that the model allows for fully explicit yet non-trivial solutions of the resulting Euler-scale hydrodynamic equations. Comparing with exact analytical non-equilibrium results valid at all time and length scales, we show perfect agreement at the Euler scale when the interactions are short range. A formal proof of the emergence of generalized hydrodynamics in the non-local Luttinger model is also given, and effects of long-range interactions are briefly discussed.
- arXiv:2003.10994 [pdf, other]
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Title: Dynamical solitons and boson fractionalization in cold-atom topological insulatorsAuthors: Daniel González-Cuadra, Alexandre Dauphin, Przemysław R. Grzybowski, Maciej Lewenstein, Alejandro BermudezSubjects: Quantum Gases (cond-mat.quant-gas); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Strongly Correlated Electrons (cond-mat.str-el); Quantum Physics (quant-ph)
We study the $\mathbb{Z}_2$ Bose-Hubbard model at incommensurate densities, which describes a one-dimensional system of interacting bosons whose tunneling is dressed by a dynamical $\mathbb{Z}_2$ field. At commensurate densities, the model is known to host intertwined topological phases, where long-range order coexists with non-trivial topological properties. This interplay between spontaneous symmetry breaking (SSB) and topological symmetry protection gives rise to interesting fractional topological phenomena when the system is doped to certain incommensurate fillings. In particular, we hereby show how topological defects in the $\mathbb{Z}_2$ field can appear in the ground state, connecting different SSB sectors. These defects are dynamical and can travel through the lattice carrying both a topological charge and a fractional particle number. In the hardcore limit, this phenomenon can be understood through a bulk-defect correspondence. Using a pumping argument, we show that it survives also for finite interactions, demonstrating how boson fractionalization can occur in strongly-correlated bosonic systems, the main ingredients of which have already been realized in cold-atom experiments.
- arXiv:2003.11011 [pdf, other]
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Title: Probabilistic Memristive Networks -- Part I: Application of a Master Equation to Networks of Binary ReRAM cellsSubjects: Emerging Technologies (cs.ET); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci)
The possibility of using non-deterministic circuit components has been gaining significant attention in recent years. The modeling and simulation of their circuits require novel approaches, as now the state of a circuit at an arbitrary moment in time cannot be precisely predicted. Generally, these circuits should be described in terms of probabilities, the circuit variables should be calculated on average, and correlation functions should be used to explore interrelations among the variables. In this paper we use, for the first time, a master equation to analyze the networks composed of probabilistic binary memristors. Analytical solutions of the master equation for the case of identical memristors connected in-series and in-parallel are found. Our analytical results are supplemented by results of numerical simulations that extend our findings beyond the case of identical memristors. The approach proposed in this paper facilitates the development of probabilistic/stochastic electronic circuits and advance their real-world applications.
Replacements
- arXiv:1810.11356 (replaced) [pdf]
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Title: Analysis of the magnetic and magnetocaloric properties of ALaFeMnO6 (A= Sr, Ba and Ca) double perovskitesAuthors: N. Brahiti, M. Abbasi Eskandari, M. Balli, Ch. Gauvin-Ndiaye, R. Nourafkan, A.-M.S. Tremblay, P. FournierComments: 35 pages including Supplemental materials, 17 figures. New version with additional data and extended analysisJournal-ref: Journal of Applied Physics, Vol. 127, 113905 (2020)Subjects: Materials Science (cond-mat.mtrl-sci)
In previous studies, we have reported that double perovskite La2NiMnO6 presents a non-negligible potential for room temperature magnetocaloric tasks. With the aim of improving even further the cooling performances and the working temperature range of double perovskites, we report the magnetic and magnetocaloric properties of La2MnFeO6 and ALaMnFeO6 (A = Sr, Ba, Ca) compounds. X-ray diffraction (XRD) and Rietveld refinement show that La2MnFeO6 (LMFO) and CaLaMnFeO6 (CLMFO) samples crystallize in an orthorhombic structure with the Pnma space group. However, a rhombohedral structure with the R3C space group is obtained for BaLaMnFeO6 (BLMFO) and SrLaMnFeO6 (SLMFO) samples. Substituting La by Ba or Sr in LMFO leads to a clear increase of the Curie temperature (Tc) compared to LMFO from 150 K for BLMFO up to 350 K for SLMFO. Moreover, CLMFO shows the smallest Tc down to 70 K. Ferromagnetic-like behavior is observed for SLMFO and BLMFO while CLMFO's magnetism resembles that of LMFO. A clear connection between the structural parameters and the magnetic properties of these doped LMFO samples is unveiled as the highest Tc and the largest magnetization are observed for SLMFO which shows also bond angles closest to 180{\deg} and the smallest bond lengths, thus optimizing the superexchange interaction. The partial substitution of Sr for La leads in fact to a significant magnetocaloric effect over a wide operating temperature range extending beyond 300 K. For some optimal growth conditions, its entropy change varies slowly over an unusually large temperature range, which is of clear interest from a practical point of view.
- arXiv:1812.08977 (replaced) [pdf, other]
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Title: State Variables and Constraints in Thermodynamics of Solids and Their ImplicationsAuthors: Koun ShiraiComments: 18 pagesSubjects: Statistical Mechanics (cond-mat.stat-mech)
There is a common view in thermodynamics that the behavior of a macroscopic system can be described by only a few state variables. Although this is true for many cases, it is unclear whether it is meaningful to ask how many state variables are acceptable. This is indeed a problem when solids are investigated within the framework of thermodynamics, which is scarcely discussed in textbooks. The present study gives an answer to this question: the mean values of all the atom positions of a given solid together with the internal energy constitute a commensurate set of state variables (thermodynamic coordinates, TCs). The argument begins with constructing consistent definitions of equilibrium and TCs. TCs are created by the constraints which characterize the system under consideration. The values of TCs are uniquely determined in equilibrium and the mutual relationships between them constitute the fundamental relation of equilibrium (FRE). Specific heat can be deduced from the FRE. Therefore, the TCs of a solid must be to give a full expression of the specific heat in the entire range of temperature, from which the above conclusion is deduced. Contrary to the conventional view, an infinite number of the atom positions and their microscopic characters do not conflict with the principles of thermodynamics. The most important requirement for TCs to meet is the uniqueness of their values in equilibrium against random motions of the constituent particles. This conclusion is compatible with the principle of information theory that the information needed to determine the probability distribution of states is the expectation values of statistical variables. A few working examples of TCs in solids are given.
- arXiv:1903.09447 (replaced) [pdf, ps, other]
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Title: Low temperature specific heat of 12442-type KCa_2Fe_4As_4F_2 single crystalsAuthors: Teng Wang, Jianan Chu, Jiaxin Feng, Lingling Wang, Xuguang Xu, Wei Li, Hai-Hu Wen, Xiaosong Liu, Gang MuComments: 6 pages, 4 figures, accepted by SCIENCE CHINA Physics, Mechanics & AstronomyJournal-ref: Sci. China-Phys. Mech. Astron. 63, 297412 (2020)Subjects: Superconductivity (cond-mat.supr-con)
Low-temperature specific heat (SH) is measured for the 12442-type KCa$_2$Fe$_4$As$_4$F$_2$ single crystal under different magnetic fields. A clear SH jump with the height of $\Delta C/T|_{T_c}$ = 130 mJ/mol K$^2$ is observed at the superconducting transition temperature $T_c$. It is found that the electronic SH coefficient $\Delta\gamma (H)$ quickly increases when the field is in the low-field region below 3 T and then considerably slows down the increase with a further increase in the field, which indicates a rather strong anisotropy or multi-gap feature with a small minimum in the superconducting gap(s). The temperature-dependent SH data indicates the presence of the $T^2$ term, which supplies further information and supports the picture with a line-nodal gap structure. Moreover, the onset point of the SH transition remains almost unchanged under the field as high as 9 T, which is similar to that observed in cuprates, and placed this system in the middle between the BCS limit and the Bose-Einstein condensation.
- arXiv:1903.11881 (replaced) [pdf, ps, other]
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Title: Relaxation theory for perturbed many-body quantum systems versus numerics and experimentComments: 6 pages, 4 figures (+ suppl. 30 pages, 4 figures); title changed during peer reviewJournal-ref: Phys. Rev. Lett. 124, 120602 (2020)Subjects: Statistical Mechanics (cond-mat.stat-mech); Quantum Physics (quant-ph)
An analytical prediction is established of how an isolated many-body quantum system relaxes towards its thermal long-time limit under the action of a time-independent perturbation, but still remaining sufficiently close to a reference case whose temporal relaxation is known. This is achieved within the conceptual framework of a typicality approach by showing and exploiting that the time-dependent expectation values behave very similarly for most members of a suitably chosen ensemble of perturbations. The predictions are validated by comparison with various numerical and experimental results from the literature.
- arXiv:1905.01702 (replaced) [pdf]
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Title: $Z_3$-vestigial nematic order due to superconducting fluctuations in the doped topological insulator Nb$_x$Bi$_2$Se$_3$ and Cu$_x$Bi$_2$Se$_3$Authors: Chang-woo Cho, Junying Shen, Jian Lyu, Omargeldi Atanov, Qianxue Chen, Seng Huat Lee, Yew San Hor, Dariusz Jakub Gawryluk, Ekaterina Pomjakushina, Marek Bartkowiak, Matthias Hecker, Jörg Schmalian, Rolf LortzSubjects: Superconductivity (cond-mat.supr-con)
A state of matter with a multi-component order parameter can give rise to vestigial order. In the vestigial phase, the primary order is only partially melted, leaving a remaining symmetry breaking behind, an effect driven by strong classical or quantum fluctuations. Vestigial states due to primary spin and charge-density-wave order have been discussed in the context of iron-based and cuprate materials. Here we present the observation of a partially melted superconductor in which pairing fluctuations condense at a separate phase transition and form a nematic state with broken Z3, i.e. three-state Potts-model symmetry. High-resolution thermal expansion, specific heat and magnetization measurements of the doped topological insulator NbxBi2Se3 reveal that this symmetry breaking occurs at Tnem=3.8 K above Tc=3.25 K, along with an onset of superconducting fluctuations. Thus, before Cooper pairs establish long-range coherence at Tc, they fluctuate in a way that breaks the rotational invariance at Tnem and induces a distortion of the crystalline lattice. Similar results are found for CuxBi2Se3.
- arXiv:1905.08356 (replaced) [pdf]
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Title: Pump frequency resonances for light-induced incipient superconductivity in YBa$_2$Cu$_3$O$_{6.5}$Comments: 47 pages, 21 figures, 2 tablesJournal-ref: Phys. Rev. X 10, 011053 (2020)Subjects: Superconductivity (cond-mat.supr-con); Strongly Correlated Electrons (cond-mat.str-el)
Optical excitation in the cuprates has been shown to induce transient superconducting correlations above the thermodynamic transition temperature, $T_C$, as evidenced by the terahertz frequency optical properties in the non-equilibrium state. In YBa$_2$Cu$_3$O$_{6+x}$ this phenomenon has so far been associated with the nonlinear excitation of certain lattice modes and the creation of new crystal structures. In other compounds, like La$_{2-x}$Ba$_x$CuO$_4$, similar effects were reported also for excitation at near infrared frequencies, and were interpreted as a signature of the melting of competing orders. However, to date it has not been possible to systematically tune the pump frequency widely in any one compound, to comprehensively compare the frequency dependent photo-susceptibility for this phenomenon. Here, we make use of a newly developed optical parametric amplifier, which generates widely tunable high intensity femtosecond pulses, to excite YBa$_2$Cu$_3$O$_{6.5}$ throughout the entire optical spectrum (3 - 750 THz). In the far-infrared region (3 - 25 THz), signatures of non-equilibrium superconductivity are induced only for excitation of the 16.4 THz and 19.2 THz vibrational modes that drive $c$-axis apical oxygen atomic positions. For higher driving frequencies (25 - 750 THz), a second resonance is observed around the charge transfer band edge at ~350 THz. These observations highlight the importance of coupling to the electronic structure of the CuO$_2$ planes, either mediated by a phonon or by charge transfer.
- arXiv:1906.08392 (replaced) [pdf, other]
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Title: Key biology you should have learned in physics class: Using ideal-gas mixtures to understand biomolecular machinesAuthors: Daniel M. ZuckermanComments: Corrected figure 4 caption. Am. J. Phys. 88:182-193 (2020)Subjects: Biomolecules (q-bio.BM); Soft Condensed Matter (cond-mat.soft); Biological Physics (physics.bio-ph)
The biological cell exhibits a fantastic range of behaviors, but ultimately these are governed by a handful of physical and chemical principles. Here we explore simple theory, known for decades and based on the simple thermodynamics of mixtures of ideal gases, which illuminates several key functions performed within the cell. Our focus is the free-energy-driven import and export of molecules, such as nutrients and other vital compounds, via transporter proteins. Complementary to a thermodynamic picture is a description of transporters via "mass-action" chemical kinetics, which lends further insights into biological machinery and free energy use. Both thermodynamic and kinetic descriptions can shed light on the fundamental non-equilibrium aspects of transport. On the whole, our biochemical-physics discussion will remain agnostic to chemical details, but we will see how such details ultimately enter a physical description through the example of the cellular fuel ATP.
- arXiv:1907.06369 (replaced) [pdf, ps, other]
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Title: Geometric phase and topological phase diagram of the one-dimensional $XXZ$ Heisenberg spin chain in a longitudinal fieldComments: 14pages, 6 figuresJournal-ref: https://doi.org/10.1016/j.jmmm.2020.166794Subjects: Statistical Mechanics (cond-mat.stat-mech); Strongly Correlated Electrons (cond-mat.str-el)
In this paper, we determine the geometric phase for the one-dimensional $XXZ$ Heisenberg chain with spin-$1/2$, the exchange couple $J$ and the spin anisotropy parameter $\Delta$ in a longitudinal field(LF) with the reduced field strength $h$. Using the Jordan-Wigner transformation and the mean-field theory based on the Wick's theorem, a semi-analytical theory has been developed in terms of order parameters which satisfy the self-consistent equations. The values of the order parameters are numerically computed using the matrix-product-state(MPS) method. The validity of the mean-filed theory could be checked through the comparison between the self-consistent solutions and the numerical results. Finally, we draw the the topological phase diagrams in the case $J<0$ and the case $J>0$.
- arXiv:1907.11154 (replaced) [pdf, other]
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Title: Learning the dynamics of open quantum systems from their steady statesComments: 12 pages, 7 figuresJournal-ref: New J. Phys. 22, 032001 (2020)Subjects: Quantum Physics (quant-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Quantum Gases (cond-mat.quant-gas); Strongly Correlated Electrons (cond-mat.str-el)
Recent works have shown that generic local Hamiltonians can be efficiently inferred from local measurements performed on their eigenstates or thermal states. Realistic quantum systems are often affected by dissipation and decoherence due to coupling to an external environment. This raises the question whether the steady states of such open quantum systems contain sufficient information allowing for full and efficient reconstruction of the system's dynamics. We find that such a reconstruction is possible for generic local Markovian dynamics. We propose a recovery method that uses only local measurements; for systems with finite-range interactions, the method recovers the Lindbladian acting on each spatial domain using only observables within that domain. We numerically study the accuracy of the reconstruction as a function of the number of measurements, type of open-system dynamics and system size. Interestingly, we show that couplings to external environments can in fact facilitate the reconstruction of Hamiltonians composed of commuting terms.
- arXiv:1908.02186 (replaced) [pdf, other]
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Title: $\mathbb{Z}_n$ solitons in intertwined topological phasesAuthors: Daniel González-Cuadra, Alexandre Dauphin, Przemysław R. Grzybowski, Maciej Lewenstein, Alejandro BermudezSubjects: Quantum Gases (cond-mat.quant-gas); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Strongly Correlated Electrons (cond-mat.str-el); Quantum Physics (quant-ph)
Topological phases of matter can support fractionalized quasi-particles localized at topological defects. The current understanding of these exotic excitations, based on the celebrated bulk-defect correspondence, typically relies on crude approximations where such defects are replaced by a static classical background coupled to the matter sector. In this work, we explore the strongly-correlated nature of symmetry-protected topological defects by focusing on situations where such defects arise spontaneously as dynamical solitons in intertwined topological phases, where symmetry breaking coexists with topological symmetry protection. In particular, we focus on the $\mathbb{Z}_2$ Bose-Hubbard model, a one-dimensional chain of interacting bosons coupled to $\mathbb{Z}_2$ fields, and show how solitons with $\mathbb{Z}_n$ topological charges appear for particle/hole dopings about certain commensurate fillings, extending the results of [1] beyond half filling. We show that these defects host fractionalized bosonic quasi-particles, forming bound states that travel through the system unless externally pinned, and repel each other giving rise to a fractional soliton lattice for sufficiently high densities. Moreover, we uncover the topological origin of these fractional bound excitations through a pumping mechanism, where the quantization of the inter-soliton transport allows us to establish a generalized bulk-defect correspondence. This in-depth analysis of dynamical topological defects bound to fractionalized quasi-particles, together with the possibility of implementing our model in cold-atomic experiments, paves the way for further exploration of exotic topological phenomena in strongly-correlated systems.
- arXiv:1908.07164 (replaced) [pdf]
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Title: Efficient Terahertz Harmonic Generation with Coherent Acceleration of Electrons in the Dirac Semimetal Cd3As2Authors: Bing Cheng, Natsuki Kanda, Tatsuhiko N. Ikeda, Takuya Matsuda, Peiyu Xia, Timo Schumann, Susanne Stemmer, Jiro Itatani, N. P. Armitage, Ryusuke MatsunagaJournal-ref: Phys. Rev. Lett. 124, 117402 (2020)Subjects: Materials Science (cond-mat.mtrl-sci)
We report strong terahertz (~10^12 Hz) high harmonic generation in thin films of Cd3As2, a three-dimensional Dirac semimetal at room temperature. The third harmonics is detectable with tabletop light source and can be as strong as 100 V/cm by applying the fundamental field of 6.5 kV/cm inside the film, showing an unprecedented efficiency for terahertz frequency conversion. Our time-resolved terahertz spectroscopy and calculations also clarify the microscopic mechanism of the nonlinearity originating in the coherent acceleration of Dirac electrons in momentum space. Our results provide clear insights for nonlinear current of Dirac electrons driven by terahertz field under an influence of scattering, paving the way toward novel devices for high-speed electronics and photonics based on topological semimetals.
- arXiv:1908.08064 (replaced) [pdf, other]
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Title: Random Quantum BatteriesComments: 7 pages double column + 14 supplementary material single column; minor corrections; Accepted in Phys Rev ResearchJournal-ref: Phys. Rev. Research 2, 023095 (2020)Subjects: Quantum Physics (quant-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Statistical Mechanics (cond-mat.stat-mech); Mathematical Physics (math-ph)
Quantum nano-devices are fundamental systems in quantum thermodynamics that have been the subject of profound interest in recent years. Among these, quantum batteries play a very important role. In this paper we lay down a theory of random quantum batteries and provide a systematic way of computing the average work and work fluctuations in such devices by investigating their typical behavior. We show that the performance of random quantum batteries exhibits typicality and depends only on the spectral properties of the time evolving operator, the initial state and the measuring Hamiltonian. At given revival times a random quantum battery features a quantum advantage over classical random batteries. Our method is particularly apt to be used both for exactly solvable models like the Jaynes-Cummings model or in perturbation theory, e.g., systems subject to harmonic perturbations. We also study the setting of quantum adiabatic random batteries.
- arXiv:1909.12193 (replaced) [pdf, other]
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Title: Understanding the lattice thermal conductivity of SrTiO3 from an ab initio perspectiveJournal-ref: Phys. Rev. Materials 4, 033606 (2020)Subjects: Materials Science (cond-mat.mtrl-sci)
We present a detailed analysis of the structure dependence of the lattice thermal conductivity of SrTiO3. We have used both ab initio Molecular Dynamic simulations and Density Functional Theory calculations to decouple the effect of different structural distortions on the thermal conductivity. We have identified two main mechanisms for tuning the thermal conductivity when a distortion is applied. First, the modification of the acoustic-modes energy dispersion when a change in the lattice parameters is imposed and second, the low energy polar modes. In particular and counterintuitively, we have found that an increase in the angle of the oxygen octahedral rotations increases the thermal conductivity due to its coupling to these polar modes.
- arXiv:1910.10716 (replaced) [pdf, other]
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Title: Multi-Channel Direct Detection of Light Dark Matter: Target ComparisonComments: 27 pages, 18 figuresJournal-ref: Phys. Rev. D 101, 055004 (2020)Subjects: High Energy Physics - Phenomenology (hep-ph); Materials Science (cond-mat.mtrl-sci)
Direct detection experiments for light dark matter are making enormous leaps in reaching previously unexplored model space. Several recent proposals rely on collective excitations, where the experimental sensitivity is highly dependent on detailed properties of the target material, well beyond just nucleus mass numbers as in conventional searches. It is thus important to optimize the target choice when considering which experiment to build. We carry out a comparative study of target materials across several detection channels, focusing on electron transitions and single (acoustic or optical) phonon excitations in crystals, as well as the traditional nuclear recoils. We compare materials currently in use in nuclear recoil experiments (Si, Ge, NaI, CsI, CaWO$_4$), a few which have been proposed for light dark matter experiments (GaAs, Al$_2$O$_3$, diamond), as well as 16 other promising polar crystals across all detection channels. We find that target- and dark matter model-dependent reach is largely determined by a small number of material parameters: speed of sound, electronic band gap, mass number, Born effective charge, high frequency dielectric constant, and optical phonon energies. We showcase, for each of the two benchmark models, an exemplary material which has a better reach than in any currently proposed experiment.
- arXiv:1910.14362 (replaced) [pdf, other]
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Title: Optical properties of graphene quantum dots: the role of chiral symmetryJournal-ref: 2D Materials 7 (2020) 025041Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci)
We analyse the electronic and optical properties of graphene quantum dots (GQD) using accurate \textit{ab initio} many-body $GW$ and Bethe-Salpeter calculations. We show that most pristine GQD, including structures with irregular shapes, are characterized by dark low energy singlet excitations that quench fluorescence. We rationalizqe this property by exploiting the chiral symmetry of the low energy electronic states in graphene. Edge \textit{sp}$^3$ functionalization is shown to efficiently brighten these low lying excitations by distorting the \textit{sp}$^2$ backbone planar symmetry. Such findings reveal an original indirect scenario for the influence of functionalization on the photoluminescence properties.
- arXiv:1911.02670 (replaced) [pdf]
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Title: Tetragonal FeSe as a Polymorphous NetworkSubjects: Materials Science (cond-mat.mtrl-sci); Superconductivity (cond-mat.supr-con)
The observed electronic structure of tetragonal FeSe has lower apparent symmetry than that of the macroscopic crystallographic structure. Here, for bulk tetragonal FeSe we carry out first-principles calculations on large supercells that preserve the observed global symmetry but do not artificially impose such symmetry on a local, site-by-site basis. This broken symmetry approach reveals rich phenomena including a nontrivial pair distribution function, wavefunction symmetry removal, mass enhancement and concomitant band narrowing all in substantial agreement with experiment without appealing to the traditional strongly correlated picture. DFT calculations using traditional highly symmetric unit cells taken from Bragg diffraction have to be revisited to search for possibly more stable, symmetry-broken states.
- arXiv:1911.02876 (replaced) [pdf, other]
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Title: Fractonic SuperfluidsComments: tiny changes made; 2 tables, 3 figures, 15 pages. Accepted by Phys. Rev. ResearchSubjects: Strongly Correlated Electrons (cond-mat.str-el); Quantum Gases (cond-mat.quant-gas); High Energy Physics - Theory (hep-th)
We propose a superfluid phase of ``many-fracton system'' in which charge and total dipole moments are conserved quantities. In this work, both microscopic model and long-wavelength effective theory are analyzed. We start with a second quantized microscopic model and formulate the coherent-state path-integral representation. With repulsive interactions and positive chemical potential, we calculate various properties of the resulting superfluid state and make comparison with a conventional superfluid. We deduce a highly nonlinear Euler-Lagrange equation as well as two Noether currents. We also formulate time-dependent Gross-Pitaevskii-type equations that govern hydrodynamical behaviors. We study the classical ground state wavefunction, the associated off-diagonal long range order (ODLRO), supercurrents, critical current, and unconventional topological vortices. At length scale much larger than coherence length $\xi_{\mathrm{coh}}$, we derive the effective theory of our microscopic model. Based on the effective theory, we analyze gapless Goldstone modes and specific heat capacity at low temperatures as well as the fate of ODLRO against quantum fluctuations. Several future directions, e.g., numerical analysis of Gross-Pitaevskii equations, fermionic fractons, fractonic superconductors, and cold-atom experimental realization, are discussed.
- arXiv:1912.04469 (replaced) [pdf, ps, other]
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Title: Theoretical possibilities for flat-band superconductivityAuthors: Hideo AokiComments: 6 pages, 5 figures, Proc. Int. Conf. "Superstripes 2019"Subjects: Superconductivity (cond-mat.supr-con); Strongly Correlated Electrons (cond-mat.str-el)
One novel arena for designing superconductors with high $T_C$ is the flat-band systems. A basic idea is that flat bands, arising from quantum mechanical interference, give unique opportunities for enhancing $T_C$ with (i) many pair-scattering channels between the dispersive and flat bands, and (ii) an even more interesting situation when the flat band is topological and highly entangled. Here we compare two routes, which comprise a multi-band system with a flat band coexisting with dispersive ones, and a one-band case with a portion of the band being flat. Superconductivity can be induced in both cases when the flat band or portion is "incipient" (close to, but away from, the Fermi energy). Differences are, for the multi-band case, we can exploit large entanglement associated with topological states, while for the one-band case a transition between different (d and p) wave pairings can arise. These hint at some future directions.
- arXiv:1912.11222 (replaced) [pdf]
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Title: A picture of pseudogap phase related to charge fluxesSubjects: Superconductivity (cond-mat.supr-con)
Recently, charge density fluctuations or charge fluxes attract strong interests in understanding the unconventional superconductivity. In this paper, a new emergent configuration in cuprates is identified by density functional theory simulations, called the charge pseudoplane, which exhibits the property of confining the dynamic charge flux flows. It further redefines the fundamental collective excitation in cuprates with the momentum-dependent and ultrafast localization-delocalization duality. It is shown that both pseudogap and superconducting phases can be born from and intertwined through the charge flux confinement property of the charge pseudoplane. Our experimental simulations based on the new picture provide good agreements with previous experimental results. Our work thus opens a new perspective to understand the origin of pseudogap phase and other related phases in cuprates, and further provides a critical descriptor to search and design higher temperature superconductors.
- arXiv:1912.12689 (replaced) [pdf]
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Title: Giant momentum-dependent spin splitting in centrosymmetric low Z antiferromagnetsComments: 20 pages, 5 figuresSubjects: Materials Science (cond-mat.mtrl-sci); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Quantum Physics (quant-ph)
The energy vs. crystal momentum E(k) diagram for a solid (band structure) constitutes the road map for navigating its optical, magnetic, and transport properties. By selecting crystals with specific atom types, composition and symmetries, one could design a target band structure and thus desired properties. A particularly attractive outcome would be to design energy bands that are split into spin components with a momentum-dependent splitting, as envisioned by Pekar and Rashba [Zh. Eksperim. i Teor. Fiz. 47 (1964)], enabling spintronic application. The current paper provides "design principles" for wavevector dependent spin splitting (SS) of energy bands that parallels the traditional Dresselhaus and Rashba spin-orbit coupling (SOC) - induce splitting, but originates from a fundamentally different source -- antiferromagnetism. We identify a few generic AFM prototypes with distinct SS patterns using magnetic symmetry design principles. These tools allow also the identification of specific AFM compounds with SS belonging to different prototypes. A specific compound -- centrosymmetric tetragonal MnF2 -- is used via density functional band structure calculations to quantitatively illustrate one type of AFM SS. Unlike the traditional SOC-induced effects restricted to non-centrosymmetric crystals, we show that antiferromagnetic-induced spin splitting broadens the playing field to include even centrosymmetric compounds, and gives SS comparable in magnitude to the best known ('giant') SOC effects, even without SOC, and consequently does not rely on the often-unstable high atomic number elements required for high SOC. We envision that use of the current design principles to identify an optimal antiferromagnet with spin-split energy bands would be beneficial for efficient spin-charge conversion and spin orbit torque applications without the burden of requiring compounds containing heavy elements.
- arXiv:1912.13079 (replaced) [pdf, other]
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Title: Unconventional $^{17}$O and $^{63}$Cu NMR shift components in cuprate superconductorsComments: 9 pages, 7 figuresSubjects: Superconductivity (cond-mat.supr-con)
Nuclear magnetic resonance (NMR) is a fundamental bulk probe that provides key information about the electronic properties of materials. Very recently, the analysis of all available planar copper shift as well as relaxation data proved that while the shifts cannot be understood in terms of a single temperature dependent spin component, relaxation can be explained with one dominating Fermi liquid-like component, without enhanced electronic spin fluctuations. For the shifts, a doping dependent isotropic term, as well as doping independent anisotropic term became obvious. Here we focus on planar $^{17}$O NMR shifts and quadrupole splittings. Surprisingly, we find that they demand, independently, a similar two-component scenario and confirm most of the previous conclusions concerning the properties of the spin components, in particular that a negative spin polarization survives in the superconducting state. This should have consequences for the pairing scenario.
- arXiv:2001.00956 (replaced) [pdf, other]
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Title: Perfect Absorption in Complex Scattering Systems with or without Hidden SymmetriesComments: Revised description for the chaotic setting, results unchanged. References addedSubjects: Disordered Systems and Neural Networks (cond-mat.dis-nn); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Chaotic Dynamics (nlin.CD); Optics (physics.optics)
Wavefront shaping (WFS) schemes for efficient energy deposition in weakly lossy targets is an ongoing challenge for many classical wave technologies relevant to next-generation telecommunications, long-range wireless power transfer, and electromagnetic warfare. In many circumstances these targets are embedded inside complicated enclosures, such as complex networks, buildings, or vessels, where the hypersensitive nature of chaotic scattering challenges the viability of WFS protocols. We demonstrate the success of a new and general WFS scheme, based on coherent perfect absorption (CPA) electromagnetic protocols, by utilizing a generic complex scattering system - a network of coupled transmission lines with complex connectivity. Our platform allows for control of the local losses inside the network and of the violation of time-reversal symmetry via a magnetic field. Our platform allows us to go beyond the initial concept of CPA as the time-reversal of a laser cavity and provides a more general framework where WFS in wave chaotic systems can be investigated using semiclassical tools, thus opening up CPA to much broader relevance in the real world.
- arXiv:2002.01308 (replaced) [src]
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Title: Integrated Photonic FFT for Optical Convolutions towards Efficient and High-Speed Neural NetworksComments: Revisions requiredSubjects: Optics (physics.optics); Disordered Systems and Neural Networks (cond-mat.dis-nn); Emerging Technologies (cs.ET)
The technologically-relevant task of feature extraction from data performed in deep-learning systems is routinely accomplished as repeated fast Fourier transforms (FFT) electronically in prevalent domain-specific architectures such as in graphics processing units (GPUs). However, electronics systems are limited with respect to power dissipation and delay, both, due to wire-charging challenges related to interconnect capacitance. Here we present a silicon photonics-based architecture for convolutional neural networks that harnesses the phase property of light to perform FFTs efficiently by executing the convolution as a multiplication in the Fourier-domain. The algorithmic executing time is determined by the time-of-flight of the signal through this photonic reconfigurable passive FFT filter circuit and is on the order of 10s of picosecond. A sensitivity analysis shows that this optical processor must be thermally phase stabilized corresponding to a few degrees. Furthermore, we find that for a small sample number, the obtainable number of convolutions per {time-power-chip area) outperforms GPUs by about 2 orders of magnitude. Lastly, we show that, conceptually, the optical FFT and convolution-processing performance is indeed directly linked to optoelectronic device-level, and improvements in plasmonics, metamaterials or nanophotonics are fueling next generation densely interconnected intelligent photonic circuits with relevance for edge-computing 5G networks.
- arXiv:2002.05847 (replaced) [pdf, ps, other]
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Title: Conductance quantization and shot noise of a double-layer quantum point contactComments: 13 pages, 16 figures, 74 referencesJournal-ref: Phys. Rev. B 101,115401 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
The conductance quantization and shot noise below the first conductance plateau $G_0 = 2e^2/h$ are measured in a quantum point contact fabricated in a GaAs/AlGaAs tunnel-coupled double quantum well. From the conductance measurement, we observe a clear quantized conductance plateau at $0.5G_0$ and a small minimum in the transconductance at $0.7 G_0$. Spectroscopic transconductance measurement reveals three maxima inside the first diamond, thus suggesting three minima in the dispersion relation for electric subbands. Shot noise measurement shows that the Fano factor behavior is consistent with this observation. We propose a model that relates these features to a wavenumber directional split subband due to a strong Rashba spin--orbit interaction that is induced by the center barrier potential gradient of the double-layer sample.
- arXiv:2002.06937 (replaced) [pdf, other]
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Title: A Dark Matter Interpretation of Excesses in Multiple Direct Detection ExperimentsComments: 20 pages, 7 figures. Submitted to PRDSubjects: High Energy Physics - Phenomenology (hep-ph); Cosmology and Nongalactic Astrophysics (astro-ph.CO); Materials Science (cond-mat.mtrl-sci); High Energy Physics - Experiment (hep-ex); Instrumentation and Detectors (physics.ins-det)
We present a novel unifying interpretation of excess event rates observed in several dark matter direct-detection experiments that utilize single-electron threshold semiconductor detectors. Despite their different locations, exposures, readout techniques, detector composition, and operating depths, these experiments all observe statistically significant excess event rates of $\sim$ 10 Hz/kg. However, none of these persistent excesses has yet been reported as a dark matter signal because individually, each can be attributed to different well-motivated but unmodeled backgrounds, and taken together, they cannot be explained by dark matter particles scattering elastically off detector nuclei or electrons. We show that these results can be reconciled if the semiconductor detectors are seeing a collective inelastic process, consistent with exciting a plasmon. We further show that plasmon excitation could arise in two compelling dark matter scenarios, both of which can explain rates of existing signal excesses in germanium and, at least at the order of magnitude level, across several single-electron threshold detectors. At least one of these scenarios also yields the correct relic density from thermal freeze-out. Both dark matter scenarios motivate a radical rethinking of the standard interpretations of dark matter-electron scattering from recent experiments.
- arXiv:2002.07730 (replaced) [pdf, other]
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Title: What limits the simulation of quantum computers?Comments: New data added, 14 figuresSubjects: Quantum Physics (quant-ph); Strongly Correlated Electrons (cond-mat.str-el)
It is imperative that useful quantum computers be very difficult to simulate classically; otherwise classical computers could be used for the applications envisioned for the quantum ones. Perfect quantum computers are unarguably exponentially difficult to simulate: the classical resources required grow exponentially with the number of qubits $N$ or the depth $D$ of the circuit. Real quantum computing devices, however, are characterized by an exponentially decaying fidelity $\mathcal{F} \sim (1-\epsilon)^{ND}$ with an error rate $\epsilon$ per operation as small as $\approx 1\%$ for current devices. In this work, we demonstrate that real quantum computers can be simulated at a tiny fraction of the cost that would be needed for a perfect quantum computer. Our algorithms compress the representations of quantum wavefunctions using matrix product states (MPS), which capture states with low to moderate entanglement very accurately. This compression introduces a finite error rate $\epsilon$ so that the algorithms closely mimic the behavior of real quantum computing devices. The computing time of our algorithm increases only linearly with $N$ and $D$. We illustrate our algorithms with simulations of random circuits for qubits connected in both one and two dimensional lattices. We find that $\epsilon$ can be decreased at a polynomial cost in computing power down to a minimum error $\epsilon_\infty$. Getting below $\epsilon_\infty$ requires computing resources that increase exponentially with $\epsilon_\infty/\epsilon$. For a two dimensional array of $N=54$ qubits and a circuit with Control-Z gates, error rates better than state-of-the-art devices can be obtained on a laptop in a few hours. For more complex gates such as a swap gate followed by a controlled rotation, the error rate increases by a factor three for similar computing time.
- arXiv:2002.09903 (replaced) [pdf, other]
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Title: NMR shift and relaxation and the electronic spin of superconducting cupratesComments: 7 pages, 5 figuresJournal-ref: J Supercond Nov Magn 2020Subjects: Superconductivity (cond-mat.supr-con)
Very recently, there has been significant progress with establishing a common phenomenology of the superconducting cuprates in terms of nuclear magnetic resonance (NMR) shift and relaxation. Different from the old interpretation, it was shown that the shifts demand two coupled spin components with different temperature dependencies. One spin component couples isotropically to the planar Cu nucleus and is likely to reside at planar O, while the other, anisotropic component has its origin in the planar copper $3d(x^2-y^2)$ orbital. Nuclear relaxation, on the other hand, was found to be rather ubiquitous and Fermi liquid-like for planar Cu, i.e., it is independent of doping and material, apart from the sudden drop at the superconducting transition temperature, $T_{\rm c}$. However, there is a doping and material dependent anisotropy that is independent on temperature, above and below $T_{\rm c}$. Here we present a slightly different analysis of the shifts that fits all planar Cu shift data. In addition we are able to derive a simple model that explains nuclear relaxation based on these two spin components. In particular, the only outlier so far, \lsco, can be understood, as well. While this concerns predominantly planar Cu, it is argued that the two component model should fit all cuprate shift and relaxation data.
- arXiv:2002.12059 (replaced) [pdf, other]
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Title: Quantum-heat fluctuation relations in $3$-level systems under projective measurementsComments: 12 Pages, 6 Figures. Contribution to the Special Issue "Many Body Quantum Chaos" in honour of Shmuel Fishman, published in the journal "Condensed Matter"Journal-ref: Condens. Matter 5 (1), 17 (2020)Subjects: Quantum Physics (quant-ph); Statistical Mechanics (cond-mat.stat-mech)
We study the statistics of energy fluctuations in a three-level quantum system subject to a sequence of projective quantum measurements. We check that, as expected, the quantum Jarzynski equality holds provided that the initial state is thermal. The latter condition is trivially satisfied for two-level systems, while this is generally no longer true for $N$-level systems, with $N > 2$. Focusing on three-level systems, we discuss the occurrence of a unique energy scale factor $\beta_{\rm eff}$ that formally plays the role of an effective inverse temperature in the Jarzynski equality. To this aim, we introduce a suitable parametrization of the initial state in terms of a thermal and a non-thermal component. We determine the value of $\beta_{\rm eff}$ for a large number of measurements and study its dependence on the initial state. Our predictions could be checked experimentally in quantum optics.
- arXiv:2003.03846 (replaced) [pdf, ps, other]
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Title: Normal density and moment of inertia of a moving superfluidComments: 6 pagesSubjects: Quantum Gases (cond-mat.quant-gas)
In this work, the normal density $\rho_n$ and moment of inertia of a moving superfluid are investigated. We find that, even at zero temperature, there exists a finite normal density for the moving superfluid. When the velocity of superfluid reaches sound velocity, the normal density becomes total mass density $\rho$, which indicates that the system losses superfluidity. At the same time, the Landau's critical velocity also becomes zero. The existence of the non-zero normal density is attributed to the coupling between the motion of superflow and density fluctuation in transverse directions. With Josephson relation, the superfluid density $\rho_s$ is also calculated and the identity $\rho_s+\rho_n=\rho$ holds. Further more, we find that the finite normal density also results in a quantized moment of inertia in a moving superfluid trapped by a ring. The normal density and moment of inertia at zero temperature could be verified experimentally by measuring the angular momentum of a moving superfluid in a ring trap.
- arXiv:2003.04362 (replaced) [pdf, other]
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Title: Monte Carlo study of the tip region of branching random walks evolved to large timesComments: 20 pages, 10 figures. v2: discussion of the unconditioned case in Sec. 3 improved, conclusions unchangedSubjects: Statistical Mechanics (cond-mat.stat-mech); High Energy Physics - Phenomenology (hep-ph)
We implement a discretization of the one-dimensional branching Brownian motion in the form of a Monte Carlo event generator, designed to efficiently produce ensembles of realizations in which the rightmost lead particle at the final time $T$ is constrained to have a position $X$ larger than some predefined value $X_{\text{min}}$. The latter may be chosen arbitrarily far from the expectation value of $X$, and the evolution time after which observables on the particle density near the lead particle are measured may be as large as $T\sim 10^4$. We then calculate numerically the probability distribution $p_n(\Delta x)$ of the number $n$ of particles in the interval $[X-\Delta x,X]$ as a function of $\Delta x$. When $X_{\text{min}}$ is significantly smaller than the expectation value of the position of the rightmost lead particle, i.e. when $X$ is effectively unconstrained, we check that both the mean and the typical values of $n$ grow exponentially with $\Delta x$, up to a linear prefactor and to finite-$T$ corrections. When $X_{\text{min}}$ is picked far ahead of the latter but within a region extending over a size of order $\sqrt{T}$ to its right, the mean value of the particle number still grows exponentially with $\Delta x$, but its typical value is lower by a multiplicative factor consistent with $e^{-\zeta\Delta x^{2/3}}$, where $\zeta$ is a number of order unity. These numerical results bring strong support to recent analytical calculations and conjectures in the infinite-time limit.
- arXiv:2003.04849 (replaced) [pdf, other]
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Title: Evidence for unbounded growth of the number entropy in many-body localized phasesSubjects: Disordered Systems and Neural Networks (cond-mat.dis-nn); Quantum Gases (cond-mat.quant-gas); Strongly Correlated Electrons (cond-mat.str-el)
We investigate the number entropy $S_N$---which characterizes particle-number fluctuations between subsystems---following a quench in one-dimensional interacting many-body systems with potential disorder. We find evidence that in the regime which is expected to show many-body localization (MBL) and where the entanglement entropy grows as $S\sim \ln t$ as function of time $t$, the number entropy grows as $S_N\sim\ln\ln t$, indicating continuing particle transport at a very slow rate. We demonstrate that this growth is consistent with a relation between entanglement and number entropy recently established for non-interacting systems.
- arXiv:2003.05723 (replaced) [pdf, other]
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Title: Superconductor-Insulator Transition and the Crossover to Non Equilibrium in two-dimensional Indium - Indium-Oxide compositeComments: 5 pages, 6 figuresSubjects: Superconductivity (cond-mat.supr-con)
Magnetic-field tuned superconductor to insulator transition was observed in a novel hybrid system of granular superconducting indium, deposited on indium oxide thin film, which exhibits global superconductivity at low magnetic fields. We have used annealing to tune the coupling to lie just at the borderline where superconductivity in the underlying InOx is suppressed, which is also close to the metal-insulator transition of the InOx. The hybrid system exhibits a "giant" magnetoresistance above the H-SIT, with critical behavior that manifests the duality between Cooper pairs and vortices.
- arXiv:2003.08651 (replaced) [pdf]
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Title: Energy Transfer within the Hydrogen Bonding Network of Water Following Resonant Terahertz ExcitationAuthors: Hossam Elgabarty, Tobias Kampfrath, Douwe Jan Bonthuis, Vasileios Balos, Naveen Kumar Kaliannan, Philip Loche, Roland R. Netz, Martin Wolf, Thomas D. Kühne, Mohsen SajadiSubjects: Soft Condensed Matter (cond-mat.soft); Chemical Physics (physics.chem-ph)
Energy dissipation in water is very fast and more efficient than in many other liquids. This behavior is commonly attributed to the intermolecular interactions associated with hydrogen bonding. Here, we investigate the dynamic energy flow in the hydrogen-bond network of liquid water by a pump-probe experiment. We resonantly excite intermolecular degrees of freedom with ultrashort single-cycle terahertz pulses and monitor its Raman response. By using ultrathin sample-cell windows, a background-free bipolar signal whose tail relaxes mono-exponentially is obtained. The relaxation is attributed to the molecular translational motions, using complementary experiments, force-field and ab initio molecular dynamics simulations. They reveal an initial coupling of the terahertz electric field to the molecular rotational degrees of freedom whose energy is rapidly transferred, within the excitation pulse duration, to the restricted-translational motion of neighboring molecules. This rapid energy transfer may be rationalized by the strong anharmonicity of the intermolecular interactions.
- arXiv:2003.08868 (replaced) [pdf]
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Title: Ostwald growth rate in controlled Covid-19 epidemic spreading as in arrested growth in quantum complex matterComments: 2 figures, 7 pagesJournal-ref: Condens. Matter 2020, 5, 23Subjects: Physics and Society (physics.soc-ph); Other Condensed Matter (cond-mat.other); Populations and Evolution (q-bio.PE)
Here, we focus on the data analysis of the growth of epidemic spread of Covid-19 in countries where different policies of containment were activated. It is known that the growth of pandemic spread at its threshold is exponential, but it is not known how to quantify the success of different containment policies. We identify that a successful approach gives an arrested phase regime following the Ostwald growth, where, over the course of time, one phase transforms into another metastable phase with a similar free energy as observed in oxygen interstitial diffusion in quantum complex matter and in crystallization of proteins. We introduce the s factor which provides a quantitative measure of the efficiency and speed of the adopted containment policy, which is very helpful not only to monitor the Covid-19 pandemic spread but also for other countries to choose the best containment policy. The results show that a policy based on joint confinement, targeted tests, and tracking positive cases is the most rapid pandemic containment policy; in fact, we found values of 9, 5, and 31 for the success s factor for China, South Korea, and Italy, respectively, where the lowest s factor indicates the best containment policy
- arXiv:2003.10302 (replaced) [pdf]
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Title: The collision frequency of electron-neutral-particle in the weakly ionized plasma with the power-law velocity distributionComments: 11 pages, 43 references, 3 figuresJournal-ref: Contrib.Plasma Phys. 60 (2020) e201900183Subjects: Plasma Physics (physics.plasm-ph); Statistical Mechanics (cond-mat.stat-mech)
We study the collision frequency of electron-neutral-particle in the weakly ionized plasma with the power-law velocity q-distribution and derive the formulation of the average collision frequency. We find that the average collision frequency in the q-distributed plasma also depends strongly on the q-parameter and thus is generally different from that in the Maxwell-distributed plasma, which therefore modifies the transport coefficients in the previous studies of the weakly ionized plasmas with the power-law velocity distributions.
- arXiv:1808.08203 (replaced) [pdf, ps, other]
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Title: On a fragmented condensate in a uniform Bose systemAuthors: Maksim TomchenkoComments: 22 pages, 3 figures; v.2: Section 2 is extended, Figs. 2, 3 and Table 1 are addedJournal-ref: J. Low Temp. Phys. 198, 100 (2020)Subjects: Quantum Gases (cond-mat.quant-gas)
According to the well-known analysis by Nozi\'{e}res, the fragmentation of the condensate increases the energy of a uniform interacting Bose system. Therefore, at $T= 0$ the condensate should be nonfragmented. We perform a more detailed analysis and show that the result by Nozi\'{e}res is not general. We find that, in a dense Bose system, the formation of a crystal-like structure with a fragmented condensate is possible. The effect is related to a nonzero size of real atoms. Moreover, the wave functions studied by Nozi\'{e}res are not eigenfunctions of the Hamiltonian and, therefore, do not allow one to judge with confidence about the structure of the condensate in the ground state. We have constructed the wave functions in such a way that they are eigenfunctions of the Hamiltonian. The results show that the fragmentation of the condensate (quasicondensate) is possible for a finite one-dimensional uniform system at low temperatures and a weak coupling.
- arXiv:1809.08708 (replaced) [pdf, other]
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Title: Transport evidence for three dimensional topological superconductivity in doped $β$-PdBi$_2$Journal-ref: Scientific Reports volume 9, Article number: 12504 (2019)Subjects: Superconductivity (cond-mat.supr-con)
Interest in topological states of matter exploded over a decade ago with the theoretical prediction and experimental detection of three-dimensional topological insulators, especially in bulk materials that can be tuned out of it by doping. However, their superconducting counterpart, the time-reversal invariant three-dimensional topological superconductor, has evaded discovery thus far. In this work, we provide transport evidence that K-doped $\beta$-PdBi$_2$ is a 3D time-reversal-invariant topological superconductor. In particular, we find signatures of Majorana surface states protected by time-reversal symmetry--the hallmark of this phase--in soft point-contact spectroscopy, while the bulk system shows signatures of odd-parity pairing via upper-critical field and magnetization measurements. Odd-parity pairing can be argued, using existing knowledge of the band structure of $\beta$-PdBi$_2$, to result in 3D topological superconductivity. Moreover, we find that the undoped system is a trivial superconductor. Thus, we discover $\beta$-PdBi$_2$ as a unique material that, on doping, can potentially undergo an unprecedented topological quantum phase transition in the superconducting state.
- arXiv:1906.04266 (replaced) [pdf, ps, other]
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Title: Phylogenetic correlations can suffice to infer protein partners from sequencesComments: 31 pages, 14 figuresJournal-ref: PLoS Comput. Biol. 15(10): e1007179 (2019)Subjects: Biomolecules (q-bio.BM); Statistical Mechanics (cond-mat.stat-mech); Biological Physics (physics.bio-ph); Quantitative Methods (q-bio.QM)
Determining which proteins interact together is crucial to a systems-level understanding of the cell. Recently, algorithms based on Direct Coupling Analysis (DCA) pairwise maximum-entropy models have allowed to identify interaction partners among paralogous proteins from sequence data. This success of DCA at predicting protein-protein interactions could be mainly based on its known ability to identify pairs of residues that are in contact in the three-dimensional structure of protein complexes and that coevolve to remain physicochemically complementary. However, interacting proteins possess similar evolutionary histories. What is the role of purely phylogenetic correlations in the performance of DCA-based methods to infer interaction partners? To address this question, we employ controlled synthetic data that only involve phylogeny and no interactions or contacts. We find that DCA accurately identifies the pairs of synthetic sequences that share evolutionary history. While phylogenetic correlations confound the identification of contacting residues by DCA, they are thus useful to predict interacting partners among paralogs. We find that DCA performs as well as phylogenetic methods to this end, and slightly better than them with large and accurate training sets. Employing DCA or phylogenetic methods within an Iterative Pairing Algorithm (IPA) allows to predict pairs of evolutionary partners without a training set. We demonstrate the ability of these various methods to correctly predict pairings among real paralogous proteins with genome proximity but no known physical interaction, illustrating the importance of phylogenetic correlations in natural data. However, for physically interacting and strongly coevolving proteins, DCA and mutual information outperform phylogenetic methods. We discuss how to distinguish physically interacting proteins from those only sharing evolutionary history.
- arXiv:1910.09967 (replaced) [pdf, other]
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Title: Entanglement entropies of inhomogeneous Luttinger liquidsComments: 19 pages, 4 figuresJournal-ref: J. Phys. A: Math. Theor.53 155001 (2020)Subjects: Statistical Mechanics (cond-mat.stat-mech); Quantum Gases (cond-mat.quant-gas); Strongly Correlated Electrons (cond-mat.str-el)
We develop a general framework to compute the scaling of entanglement entropy in inhomogeneous one-dimensional quantum systems belonging to the Luttinger liquid universality class. While much insight has been gained in homogeneous systems by making use of conformal field theory techniques, our focus is on systems for which the Luttinger parameter $K$ depends on position, and conformal invariance is broken. An important point of our analysis is that contributions stemming from the UV cutoff have to be treated very carefully, since they now depend on position. We show that such terms can be removed either by considering regularized entropies specifically designed to do so, or by tabulating numerically the cutoff, and reconstructing its contribution to the entropy through the local density approximation. We check our method numerically in the spin-1/2 XXZ spin chain in a spatially varying magnetic field, and find excellent agreement.
- arXiv:1910.10173 (replaced) [pdf, other]
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Title: Low-rank Sachdev-Ye-Kitaev modelsComments: 5+10 pages, 10 figuresJournal-ref: Phys. Rev. B 101, 125112 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el); High Energy Physics - Theory (hep-th); Quantum Physics (quant-ph)
Motivated by recent works on atom-cavity realizations of fast scramblers, and on Cooper pairing in non-Fermi liquids, we study a family of solvable variants of the ($q=4$) Sachdev-Ye-Kitaev model in which the rank and eigenvalue distribution of the coupling matrix $J_{ij,kl}$ are tuneable. When the rank is proportional to the number of fermions, the low temperature behavior is sensitive to the eigenvalue distribution. We obtain a complete classification of the possible non-Fermi liquid quantum phases. These include two previously studied phases whose fermion scaling dimension depends continuously on the rank; we show that they are maximally chaotic, but necessitate {an extensively degenerate or negative semidefinite coupling matrix}. More generic distributions give rise to "almost Fermi liquids" with a scaling dimension $\Delta = 1/2$, but which differ from a genuine Fermi-liquid in quasi-particle decay rate, quantum Lyapunov exponent and/or specific heat.
- arXiv:1910.10183 (replaced) [pdf, other]
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Title: Catastrophe theory classification of Fermi surface topological transitions in two dimensionsJournal-ref: Phys. Rev. Research 2, 013355 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el); Materials Science (cond-mat.mtrl-sci)
We classify all possible singularities in the electronic dispersion of two-dimensional systems that occur when the Fermi surface changes topology, using catastrophe theory. For systems with up to seven control parameters (i.e., pressure, strain, bias voltage, etc), the theory guarantees that the singularity belongs to to one of seventeen standard types. We show that at each of these singularities the density of states diverges as a power law, with a universal exponent characteristic of the particular catastrophe, and we provide its universal ratio of amplitudes of the prefactors of energies above and below the singularity. We further show that crystal symmetry restricts which types of catastrophes can occur at the points of high symmetry in the Brillouin zone. For each of the seventeen wallpaper groups in two-dimensions, we list which catastrophes are possible at each high symmetry point.
- arXiv:1910.10585 (replaced) [pdf, other]
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Title: Boundary-induced effect encoded in the corrections to the geometric phase acquired by a bipartite two-level systemComments: 12 pages, 9 figuresJournal-ref: Phys. Rev. A 101, 032337 (2020)Subjects: Quantum Physics (quant-ph); Other Condensed Matter (cond-mat.other)
We present a bipartite two-level system coupled to electromagnetic quantum vacuum fluctuations through a general dipolar coupling. We derive the master equation in the framework of open quantum systems, assuming an environment composed of (i) solely vacuum fluctuations and (ii) the vacuum fluctuations and a conducting plate located at a fixed distance from the bipartite system. For both cases considered, we study the dynamics of the bipartite system and the temporal evolution of the concurrence of an initial entangled bipartite state. We further analyze the generation of entanglement due to the vacuum structure. Finally, we study the different induced contributions to the correction of the unitary geometric phase of a bipartite quantum state so as to explore the possibility of future experimental setups by considering the influence of boundaries conditions in vacuum
- arXiv:1911.07660 (replaced) [pdf, other]
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Title: Renormalization Group in the Problem of Active Scalar AdvectionJournal-ref: http://www.pdmi.ras.ru/znsl/2019/v487/abs005.htmlSubjects: Statistical Mechanics (cond-mat.stat-mech)
The field theoretic renormalization group (RG) is applied to the model of a near-equilibrium fluid coupled to a scalar field (like temperature or density of an impurity) which is active, that is, influencing the dynamics of the fluid itself. It is shown that the only possible nontrivial infrared (IR) asymptotic regimes are governed by "passive" fixed points of the RG equations, where the back reaction is irrelevant. This result reminds of that obtained in [Nandy and Bhattacharjee, J. Phys. A: Math. Gen. {\bf 31}, 2621 (1998)] in a model describing active convection by fully developed turbulence. Furthermore, we establish the existence of "exotic" fixed points with negative and complex effective couplings and transport coefficients that may suggest possible directions for future studies.
- arXiv:1912.01033 (replaced) [pdf, other]
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Title: Modified instanton sum in QCD and higher-groupsComments: 31 pages, 1 figure; (v2) new explanation added, typos fixed, references addedJournal-ref: JHEP03 (2020) 123Subjects: High Energy Physics - Theory (hep-th); Strongly Correlated Electrons (cond-mat.str-el); High Energy Physics - Lattice (hep-lat); High Energy Physics - Phenomenology (hep-ph)
We consider the $SU(N)$ Yang-Mills theory, whose topological sectors are restricted to the instanton number with integer multiples of $p$. We can formulate such a quantum field theory maintaining locality and unitarity, and the model contains both $2\pi$-periodic scalar and $3$-form gauge fields. This can be interpreted as coupling a topological theory to Yang-Mills theory, so the local dynamics becomes identical with that of pure Yang-Mills theory. The theory has not only $\mathbb{Z}_N$ $1$-form symmetry but also $\mathbb{Z}_p$ $3$-form symmetry, and we study the global nature of this theory from the recent 't Hooft anomaly matching. The computation of 't Hooft anomaly incorporates an intriguing higher-group structure. We also carefully examine that how such kinematical constraint is realized in the dynamics by using the large-$N$ and also the reliable semiclassics on $\mathbb{R}^3\times S^1$, and we find that the topological susceptibility plays a role of the order parameter for the $\mathbb{Z}_p$ $3$-form symmetry. Introducing a fermion in the fundamental or adjoint representation, we find that the chiral symmetry becomes larger than the usual case by $\mathbb{Z}_p$, and it leads to the extra $p$ vacua by discrete chiral symmetry breaking. No dynamical domain wall can interpolate those extra vacua since such objects must be charged under the $3$-form symmetry in order to match the 't Hooft anomaly.
- arXiv:1912.02505 (replaced) [pdf, other]
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Title: Continuous feedback on a quantum gas coupled to an optical cavityAuthors: Katrin Kroeger, Nishant Dogra, Rodrigo Rosa-Medina, Marcin Paluch, Francesco Ferri, Tobias Donner, Tilman EsslingerComments: 15 pages, 5 figuresJournal-ref: New J. Phys. 22 (2020) 033020Subjects: Quantum Gases (cond-mat.quant-gas)
We present an active feedback scheme acting continuously on the state of a quantum gas dispersively coupled to a high-finesse optical cavity. The quantum gas is subject to a transverse pump laser field inducing a self-organization phase transition, where the gas acquires a density modulation and photons are scattered into the resonator. Photons leaking from the cavity allow for a real-time and non-destructive readout of the system. We stabilize the mean intra-cavity photon number through a micro-processor controlled feedback architecture acting on the intensity of the transverse pump field. The feedback scheme can keep the mean intra-cavity photon number $n_\text{ph}$ constant, in a range between $n_\text{ph}=0.17\pm 0.04$ and $n_\text{ph}=27.6\pm 0.5$, and for up to 4 s. Thus we can engage the stabilization in a regime where the system is very close to criticality as well as deep in the self-organized phase. The presented scheme allows us to approach the self-organization phase transition in a highly controlled manner and is a first step on the path towards the realization of many-body phases driven by tailored feedback mechanisms.
- arXiv:1912.09699 (replaced) [pdf, other]
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Title: Spatial BCS-BEC crossover in superconducting p-n junctionsComments: 10 pages, 17 figures, accepted for publication in Phys. Rev. B (2020)Journal-ref: Phys. Rev. B 101, 094514 (2020)Subjects: Superconductivity (cond-mat.supr-con); Quantum Gases (cond-mat.quant-gas); Quantum Physics (quant-ph)
We present a theory of superconducting p-n junctions. We consider a 2-band model of doped bulk semiconductors with attractive interactions between the charge carriers and derive the superconducting order parameter, the quasiparticle density of states and the chemical potential as a function of semiconductor gap $\Delta_0$ and the doping level $\varepsilon$. We verify previous results for the quantum phase diagram (QPD) for a system with constant density of states in the conduction and valence band, which show BCS-Superconductor to Bose-Einstein-Condensation (BEC) and BEC to Insulator transitions as function of doping level and band gap. Then, we extend it to a 3D density of states and derive the QPD, finding that a BEC phase can only exist for small band gaps $\Delta_0 < \Delta_0^*$. For larger band gaps, there is a direct transition from an insulator to a BCS phase. Next, we apply this theory to study the properties of superconducting p-n junctions, deriving the spatial variation of the superconducting order parameter along the p-n junction. We find a spatial crossover between a BCS and BEC condensate, as the density of charge carriers changes across the p-n junction. For the 2D system, we find two regimes, when the bulk is in a BCS phase, a BCS-BEC-BCS junction with a single BEC layer, and a BCS-BEC-I-BEC-BCS junction with two layers of BEC condensates separated by an insulating layer. In 3D there can also be a conventional BCS-I-BCS junction for semiconductors with band gaps exceeding $\Delta_0^*$. Thus, there can be BEC layers in the well controlled setting of doped semiconductors, where the doping level can be varied to change the thickness of BEC layers, making Bose Einstein Condensates possibly accessible to experimental transport and optical studies in solid state materials.
- arXiv:1912.10956 (replaced) [pdf, other]
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Title: Statistical physics of interacting proteins: impact of dataset size and quality assessed in synthetic sequencesComments: 18 pages, 16 figuresJournal-ref: Phys. Rev. E 101, 032413 (2020)Subjects: Biomolecules (q-bio.BM); Statistical Mechanics (cond-mat.stat-mech); Biological Physics (physics.bio-ph)
Identifying protein-protein interactions is crucial for a systems-level understanding of the cell. Recently, algorithms based on inverse statistical physics, e.g. Direct Coupling Analysis (DCA), have allowed to use evolutionarily related sequences to address two conceptually related inference tasks: finding pairs of interacting proteins, and identifying pairs of residues which form contacts between interacting proteins. Here we address two underlying questions: How are the performances of both inference tasks related? How does performance depend on dataset size and the quality? To this end, we formalize both tasks using Ising models defined over stochastic block models, with individual blocks representing single proteins, and inter-block couplings protein-protein interactions; controlled synthetic sequence data are generated by Monte-Carlo simulations. We show that DCA is able to address both inference tasks accurately when sufficiently large training sets are available, and that an iterative pairing algorithm (IPA) allows to make predictions even without a training set. Noise in the training data deteriorates performance. In both tasks we find a quadratic scaling relating dataset quality and size that is consistent with noise adding in square-root fashion and signal adding linearly when increasing the dataset. This implies that it is generally good to incorporate more data even if its quality is imperfect, thereby shedding light on the empirically observed performance of DCA applied to natural protein sequences.
- arXiv:2001.00443 (replaced) [pdf, other]
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Title: Band nesting and exciton spectrum in monolayer MoS$_2$Journal-ref: Phys. Rev. B 101, 125423 (2020)Subjects: Materials Science (cond-mat.mtrl-sci); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We discuss here the effect of band nesting and topology on the spectrum of excitons in a single layer of MoS$_2$, a prototype transition metal dichalcogenide material. We solve for the single particle states using the ab initio based tight-binding model containing metal $d$ and sulfur $p$ orbitals. The metal orbitals contribution evolving from $K$ to $\Gamma$ points results in conduction-valence band nesting and a set of second minima at $Q$ points in the conduction band. There are three $Q$ minima for each $K$ valley. We accurately solve the Bethe-Salpeter equation including both $K$ and $Q$ points and obtain ground and excited exciton states. We determine the effects of the electron-hole single particle energies including band nesting, direct and exchange screened Coulomb electron-hole interactions and resulting topological magnetic moments on the exciton spectrum. The ability to control different contributions combined with accurate calculations of the ground and excited exciton states allows for the determination of the importance of different contributions and a comparison with effective mass and $k\cdot p$ massive Dirac fermion models.
- arXiv:2001.06647 (replaced) [pdf]
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Title: Ambipolar Transport in Narrow Bandgap Semiconductor InSb NanowiresComments: 13 pages, 4 figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We report on transport measurement study of top-gated field effect transistors made out of InSb nanowires grown by chemical vapor deposition. The transistors exhibit ambipolar transport characteristics revealed by three distinguished gate-voltage regions: In the middle region where the fermi level resides within the bandgap, the electrical resistance shows an exponential dependence on temperature and gate voltage. With either more positive or negative gate voltages, the devices enter the electron and hole transport regimes, revealed by a resistance decreasing linearly with decreasing temperature. From the transport measurement data of a 1-$\mu$m-long device made from a nanowire of 50 nm in diameter, we extract a bandgap energy of 190-220 meV. The off-state current of this device is found to be suppressed within the measurement noise at a temperature of T = 4 K. A shorter, 260-nm-long device is found to exhibit a finite off-state current and a hole, on-state, circumference-normalized current of 11 $\mu$A/$\mu$m at V$_D$ = 50 mV which is the highest for such a device to our knowledge. The ambipolar transport characteristics make the InSb nanowires attractive for CMOS electronics, hybrid electron-hole quantum systems and hole based spin qubits.
- arXiv:2003.08025 (replaced) [pdf]
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Title: Pressure-induced inverse order-disorder transition in double perovskitesAuthors: Zheng Deng, Chang-Jong Kang, Mark Croft, Wenmin Li, Xi Shen, Jianfa Zhao, Richeng Yu, Changqing Jin, Gabi Kotliar, Sizhan Liu, T. A. Tyson, Ryan Tappero, Martha GreenblattComments: 12 pages, 4 figures, 1 tableJournal-ref: Angewandte Chemie International Edition 59, 8240 (2020)Subjects: Materials Science (cond-mat.mtrl-sci); Strongly Correlated Electrons (cond-mat.str-el)
Given the consensus that pressure improves cation order in most of known materials, a discovery of pressure-induced disorder could require reconsideration of order-disorder transition in solid state physics/chemistry and geophysics. Double perovskites Y2CoIrO6 and Y2CoRuO6 synthesized at ambient pressure show B-site order, while the polymorphs synthesized at 6 and 15 GPa are partially-ordered and disordered respectively. With the decrease of ordering degrees, the lattices are shrunken and the crystal structures alter from monoclinic to orthorhombic symmetry. Correspondingly, long-range ferrimagnetic order in the B-site ordered phases are gradually overwhelmed by B-site disorder. Theoretical calculations suggest that unusual unit cell compressions under external pressures unexpectedly stabilize the disordered phases of Y2CoIrO6 and Y2CoRuO6.
- arXiv:2003.09607 (replaced) [pdf, ps, other]
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Title: Unidirectional ripplopolaron charge transport in a three-terminal microchannel deviceComments: 5 pages, 3 figuresJournal-ref: Phys. Rev. Lett. 124, 126803 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We study the transport of surface electrons on superfluid helium through a microchannel structure in which the charge flow splits into two branches, one flowing straight and one turned at 90 degrees. According to Ohm law, an equal number of charges should flow into each branch. However, when the electrons are dressed by surface excitations (ripplons) to form polaron-like particles with sufficiently large effective mass, all the charge follows the straight path due to momentum conservation. This surface-wave induced transport is analogous to the motion of electrons coupled to surface acoustic waves in semiconductor 2DEGs.
- arXiv:2003.10099 (replaced) [pdf, ps, other]
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Title: Effective non-Hermitian physics for degenerate ground states of a nonHermitian Ising model with $\mathcal{RT}$ symmetryJournal-ref: EPL, 128 (2019) 41001Subjects: Statistical Mechanics (cond-mat.stat-mech); Quantum Physics (quant-ph)
In this paper, based on a one-dimensional non-Hermitian spin model with $\mathcal{RT}$-invariant term, we study the non-Hermitian physics for the two (nearly) degenerate ground states. By using the high-order perturbation method, an effective pseudo-spin model is obtained to describe non-Hermitian physics for the two (nearly) degenerate ground states, which are precisely consistent with the numerical calculations. We found that there may exist effective (anti) $\mathcal{PT}$ symmetry for the effective pseudo-spin model of the two (nearly) degenerate ground states. In particular, there exists spontaneous (anti) $\mathcal{PT}$ -symmetry breaking for the topological degenerate ground states with tunable parameters in external fields. We also found that even a very tiny imaginary external field applied will drive $\mathcal{PT}$ phase transition.
Crosses
- arXiv:1907.06661 (cross-list from hep-th) [pdf, other]
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Title: Quantum thermalization and Virasoro symmetryComments: 45 pages, 10 figures; v2: expanded explanations in Sections 1, 3 and 4Subjects: High Energy Physics - Theory (hep-th); Statistical Mechanics (cond-mat.stat-mech)
We initiate a systematic study of high energy matrix elements of local operators in 2d CFT. Knowledge of these is required in order to determine whether the eigenstate thermalization hypothesis (ETH) can hold in such theories. Most high energy states are high level Virasoro descendants, and by employing an oscillator representation of the Virasoro algebra we develop an efficient method for computing matrix elements of primary operators in such states. In parameter regimes where we expect (e.g. from AdS/CFT intuition) thermalization to occur, we observe striking patterns in the matrix elements: diagonal matrix elements are smoothly varying and off-diagonal elements, while nonzero, are power-law suppressed compared to the diagonal elements. We discuss the implications of these universal properties of 2d CFTs in regard to their compatibility with ETH.
Thu, 26 Mar 2020
- arXiv:2003.11023 [pdf, ps, other]
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Title: Spin-transfer torque driven intrinsic localized spin excitations in the presence of field-like torqueComments: 21 pages, 8 figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Exactly Solvable and Integrable Systems (nlin.SI)
We study the existence of intrinsic localized one-spin excitation in the Heisenberg one-dimensional ferromagnetic spin chain in the presence of perpendicular and parallel external magnetic fields and current with spin-transfer torque and field-like torque. The Landau-Lifshitz-Gilbert-Slonczewski(LLGS) equation is exactly solved for the one spin excitation in the absence of onsite anisotropy for the excitations of spin with fields perpendicular and parallel to the chain. We show the removal of damping in the spin excitations by appropriately introducing current and also the enhancement of angular frequency of the oscillations due to field-like torque in the case of both perpendicular and parallel field. The exactness of the analytical results is verified by matching with numerical counterparts. Further, we numerically confirm the existence of in-phase and anti-phase stable synchronized oscillations for two spin-excitations in the presence of current with perpendicular field and field-like torque.
- arXiv:2003.11040 [pdf, other]
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Title: Machine Learning for Quantum MatterAuthors: Juan CarrasquillaComments: 34 pages, 4 figures, 244 references. Review paperSubjects: Computational Physics (physics.comp-ph); Strongly Correlated Electrons (cond-mat.str-el); Quantum Physics (quant-ph)
Quantum matter, the research field studying phases of matter whose properties are intrinsically quantum mechanical, draws from areas as diverse as hard condensed matter physics, materials science, statistical mechanics, quantum information, quantum gravity, and large-scale numerical simulations. Recently, researchers interested quantum matter and strongly correlated quantum systems have turned their attention to the algorithms underlying modern machine learning, with an eye on making progress in their fields. Here we provide a short review on the recent development and adaptation of machine learning ideas for the purpose advancing research in quantum matter, including ideas ranging from algorithms that recognize conventional and topological states of matter in synthetic an experimental data, to representations of quantum states in terms of neural networks and their applications to the simulation and control of quantum systems. We discuss the outlook for future developments in areas at the intersection between machine learning and quantum many-body physics.
- arXiv:2003.11042 [pdf, other]
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Title: Dissipative analogue of four-dimensional quantum Hall physicsSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Optics (physics.optics); Quantum Physics (quant-ph)
The four-dimensional quantum Hall effect (QHE), which features a non-trivial configuration of three-dimensional Weyl cones on its boundaries, relies on synthetic dimensions for its simulation in experiment. Here, we propose a three-dimensional analogue of this model in the form of a dissipative Weyl semimetal (WSM) described by a non-Hermitian (NH) Hamiltonian, which in the long-time limit manifests the anomalous boundary physics of the four-dimensional QHE in the bulk spectrum. The topology of the NH WSM is captured by a three-dimensional winding number whose value is directly related to the total chirality of the surviving Weyl nodes. Upon taking open boundary conditions, instead of Fermi arcs, we find exceptional points with an order that scales with system size.
- arXiv:2003.11050 [pdf]
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Title: Electric-field-controllable high-spin SrRuO3 driven by a solid ionic junctionAuthors: Jingdi Lu, Liang Si, Xiefei Yao, Chengfeng Tian, Jing Wang, Qinghua Zhang, Zhengxun Lai, Iftikhar Ahmed Malik, Xin Liu, Peiheng Jiang, Kejia Zhu, Youguo Shi, Zhenlin Luo, Lin Gu, Karsten Held, Wenbo Mi, Zhicheng Zhong, Ce-Wen Nan, Jinxing ZhangSubjects: Strongly Correlated Electrons (cond-mat.str-el)
Controlling magnetism and spin structures in strongly correlated systems by using electric field is of fundamental importance but challenging. Here, a high-spin ruthenate phase is achieved via a solid ionic chemical junction at SrRuO3/SrTiO3 interface with distinct formation energies and diffusion barriers of oxygen vacancies, analogue to electronic band alignment in semiconductor heterojunction. Oxygen vacancies trapped within this interfacial SrRuO3 reconstruct Ru-4d electronic structure and orbital occupancy, leading to an enhanced magnetic moment. Furthermore, an interfacial magnetic phase can be switched reversibly by electric-field-rectifying oxygen migration in a solid-state ionic gating device, providing a framework for atomic design of functionalities in strongly correlated oxides using a way of solid chemistry.
- arXiv:2003.11052 [pdf]
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Title: Understanding the Quantum Oscillation Spectrum of Heavy-fermion Compound SmB6Authors: Ruiqi Zhang, Bahadur Singh, Christopher Lane, Jamin Kidd, Yubo Zhang, Bernardo Barbiellini, Robert S. Markiewicz, Arun Bansil, Jianwei SunComments: 17 pages, 7 figures and 1 tableSubjects: Strongly Correlated Electrons (cond-mat.str-el)
SmB6 is a mysterious compound that is electrically insulating but yet it exhibits quantum oscillations, which are a telltale signature of the metallic state. Adding to the enigma is the possibility that SmB6 is a topological Kondo insulator. Here, we report first-principles, parameter-free all-electron electronic-structure calculations on SmB6, which yield the band structure and crystal-field splittings within the f-electron complex in accord with experiments. Predicted energies of several magnetic phases where charge, spin and lattice degrees of freedom are treated on an equal footing are found to be extremely close, indicating the key role of spin fluctuations in SmB6. Our results show that the topological Kondo state of SmB6 is robust regardless of its magnetic configuration. The Fermi surfaces derived from our predicted ground state explain the experimentally observed bulk quantum oscillations, and our large calculated effective mass of electrons at the Fermi surface explains how the material is essentially insulating, with a measured specific heat that is in excellent agreement with our calculations.
- arXiv:2003.11056 [pdf, other]
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Title: Dephasing-rephasing dynamics of one-dimensional tunneling quasicondensatesComments: 15 pages, 4 figures; accepted for publication on New Journal of PhysicsSubjects: Quantum Gases (cond-mat.quant-gas)
We study the quantum tunneling of two one-dimensional quasi-condensates made of alkali-metal atoms, considering two different tunneling configurations: side-by-side and head-to-tail. After deriving the quasiparticle excitation spectrum, we discuss the dynamics of the relative phase following a sudden coupling of the independent subsystems. In particular, we calculate the coherence factor of the system, which, due to the nonzero tunneling amplitude, it exhibits dephasing-rephasing oscillations instead of pure dephasing. These oscillations are enhanced by a higher tunneling energy, and by higher system densities. Our predictions provide a benchmark for future experiments at temperatures below $T \lesssim 5 \, \mbox{nK}$.
- arXiv:2003.11058 [pdf, other]
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Title: Antiferromagnet-based neuromorphics using dynamics of topological chargesComments: 5 pages, 3 figures, references and supplemental materialSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Applied Physics (physics.app-ph)
We propose a spintronics-based hardware implementation of neuromorphic computing, specifically, the spiking neural network, using topological winding textures in one-dimensional antiferromagnets. The consistency of such a network is emphasized in light of the conservation of topological charges, and the natural spatiotemporal interconversions of magnetic winding. We discuss the realization of the leaky integrate-and-fire behavior of neurons and the spike-timing-dependent plasticity of synapses.
- arXiv:2003.11065 [pdf, other]
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Title: Haldane gap of the $3$-box symmetric ${\rm SU}(3)$ chainComments: 5 pages, 4 figures, + Supplemental MaterialSubjects: Strongly Correlated Electrons (cond-mat.str-el)
Motivated by the recent generalization of the Haldane conjecture to ${\rm SU}(3)$ chains [M. Lajk\'o et al., Nucl. Phys. B 924, 508 (2017)] according to which a Haldane gap should be present for symmetric representations if the number of boxes in the Young diagram is a multiple of 3, we develop a density matrix renormalization group algorithm based on standard Young tableaus to study the model with $3$ boxes directly in the representations of the global ${\rm SU}(3)$ symmetry. We show that there is a finite gap between the singlet and the symmetric $[3\,0\,0]$ sector $\Delta_{[3\,0\,0]}/J = 0.040\pm0.006$ where $J$ is the antiferromagnetic Heisenberg coupling, and we argue on the basis of the structure of the low energy states that this is sufficient to conclude that the spectrum is gapped.
- arXiv:2003.11068 [pdf, other]
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Title: Fast tunable high Q-factor superconducting microwave resonatorsSubjects: Applied Physics (physics.app-ph); Superconductivity (cond-mat.supr-con)
We present fast tunable superconducting microwave resonators fabricated from planar NbN on a sapphire substrate. The $3\lambda/4$ wavelength resonators are tuning fork shaped and tuned by passing a dc current which controls the kinetic inductance of the tuning fork prongs. The $\lambda/4$ section from the open end operates as an integrated impedance converter which creates a nearly perfect short for microwave currents at the dc terminal coupling points, thus preventing microwave energy leakage through the dc lines. We measure an internal quality factor $Q_{\rm int}>10{^{5}}$ over the entire tuning range. We demonstrate a tuning range of $> 3\%$ and tuning response times as short as 20 ns for the maximum achievable detuning. Due to the quasi-fractal design, the resonators are resilient to magnetic fields of up to 0.5 T.
- arXiv:2003.11072 [pdf, other]
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Title: Tuning electron correlation in magic-angle twisted bilayer graphene using Coulomb screeningComments: 6 pages, 4 figures plus supplementary informationSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Strongly Correlated Electrons (cond-mat.str-el); Superconductivity (cond-mat.supr-con)
The ability to control the strength of interaction is essential for understanding the mechanism underlying the quantum phenomena displayed by a correlated fermionic system. For example, the isotope effect served as an important experimental support for the electron-phonon mechanism of BCS theory of superconductivity. In addition, the ability to tune pairing strength in a fermionic cold atom system gives rise to a unique control of the crossover between the BEC and BCS regimes, uniting the strong and weak-pairing limits. In this work, we report a new device geometry where the magic-angle twisted bilayer graphene is placed in close proximity to a Bernal bilayer graphene separated by a $3$nm thick barrier. Using charge screening from the Bernal bilayer, the strength of Coulomb interaction within the twisted bilayer can be continuously tuned. This allows us to study the role of Coulomb interaction in various emergent quantum phenomena observed in the twisted bilayer using transport measurements. Our results indicate that both the insulating and superconducting phases at partial filling of the moir\'e band become less robust as Coulomb interaction is weakened by screening. This serves as direct evidence for the role of Coulomb interaction in stabilizing the superconducting phase. In addition, the effect of Coulomb screening provides important constraints for theoretical models aiming to accurately describe the mechanism and the nature of superconductivity in magic-angle twisted bilayer graphene.
- arXiv:2003.11073 [pdf, other]
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Title: Weak-ergodicity-breaking via lattice supersymmetryComments: 8 pages, 4 figuresSubjects: Statistical Mechanics (cond-mat.stat-mech); Strongly Correlated Electrons (cond-mat.str-el); High Energy Physics - Theory (hep-th); Quantum Physics (quant-ph)
We study the spectral properties of $D$-dimensional $N(1,1)$ supersymmetric lattice models. We find systematic departures from the eigenstate thermalization hypothesis (ETH) in the form of a degenerate set of ETH-violating supersymmetric (SUSY) doublets, also referred to as many-body scars, that we construct analytically. These states are stable against arbitrary SUSY-preserving perturbations, including inhomogeneous couplings. For the specific case of two-leg ladders, we provide extensive numerical evidence that shows how those states are the only ones violating the ETH, and discuss their robustness to SUSY-violating perturbations. Our work suggests a generic mechanism to stabilize quantum many-body scars in lattice models in arbitrary dimensions.
- arXiv:2003.11083 [pdf]
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Title: Quasiparticle Energies and Excitonic Effects of Chromium Trichloride, from Two Dimensions to BulkComments: 21 pages, 7 figures, and 2 tablesSubjects: Materials Science (cond-mat.mtrl-sci); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Computational Physics (physics.comp-ph)
Layered van der Waals (vdW) magnetic materials have attracted significant research interest to date. In this work, we employ the first-principles many-body perturbation theory to calculate excited-state properties of a prototype vdW magnet, chromium trichloride (CrCl3), covering monolayer, bilayer, and bulk. Unlike usual non-magnetic vdW semiconductors, in which many-electron interactions and excited states are sensitive to dimensionality, many-electron interactions are always enhanced and dominate quasiparticle energies and optical responses of both two-dimensional and bulk CrCl3. The electron-hole (e-h) binding energy can reach 3 eV in monolayer and remains as high as 2 eV in bulk. Because of the cancellation effect between self-energy corrections and e-h binding energies, the lowest-energy exciton (optical gap) is almost not affected by the change of dimensionality. Particularly, for the excitons with similar e-h binding energies, their dipole oscillator strength can differ by a few orders of magnitude. Our analysis shows that such a big difference is from a unique interference effect between e-h interactions and interband transitions. Finally, we find that the interlayer stacking sequence and magnetic coupling barely change quasiparticle band gaps and optical absorption spectra of CrCl3. Our findings give insight into the understanding of many-electron interactions and the interplay between magnetic orders and optical excitations in vdW magnetic materials.
- arXiv:2003.11088 [pdf, ps, other]
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Title: Anomalous out-of-equilibrium dynamics in the spin-ice material Dy$_2$Ti$_2$O$_7$ under moderate magnetic fieldsAuthors: Pamela C. Guruciaga, Lucas Pili, Santiago Boyeras, Demian Slobinsky, Santiago A. Grigera, Rodolfo A. BorziComments: 19 pages, 9 figuresSubjects: Statistical Mechanics (cond-mat.stat-mech); Strongly Correlated Electrons (cond-mat.str-el)
We study experimentally and numerically the dynamics of the spin ice (SI) material Dy$_2$Ti$_2$O$_7$ in the low temperature and moderate magnetic field regime ($T\in$[0.1,1.7]K, $B\in$[0,0.3]T). One of our objectives is to understand the main physics shaping the out-of-equilibrium magnetisation vs. temperature curves. We find that single crystals, as noted before for powdered samples, tend to abandon equilibrium at a blocking temperature $T_B$ which increases with applied field. Curiously, this behaviour is present even within the nearest-neighbours interactions model. Simulations and ac-susceptibility experiments show that the increasing trend in $T_B$ is stronger for fields applied along [100]. This suggests that the field plays a part in the dynamical arrest through the suppression of magnetic monopoles (localised thermal excitations in SI), which is quite manifest for this field orientation. On the other hand, very far from equilibrium the effect of $B$ is the inverse one: turning on the field after having cooled the system with zero field can increase the monopole concentration through dissociation of bound monopole pairs, thus accelerating the dynamics. The process is similar to that observed in electrolytes. However, for SI the polarisation state of the vacuum out of which the monopole pairs are created is a key factor shaping the magnetisation curves that has no analog in the electric case. We observe a threshold field near 0.2T for this fast dynamics to take place; it is linked to the maximum magnetic force possible between the attracting pair. Surprisingly, within a regime of low temperatures and moderate fields, an extended Ohm's law can be used to describe the zero-field-cooled magnetisation curve obtained with the dipolar SI model. However, in real samples the acceleration of the dynamics appears even sharper than in simulations, possibly due to the presence of avalanches.
- arXiv:2003.11093 [pdf, other]
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Title: Endoreversible Otto engines at maximal powerComments: 6 pages, 1 figure;Subjects: Statistical Mechanics (cond-mat.stat-mech)
Despite its idealizations, thermodynamics has proven its power as a predictive theory for practical applications. In particular, the Curzon-Ahlborn efficiency provides a benchmark for any real engine operating at maximal power. Here we further develop the analysis of endoreversible Otto engines. For a generic class of working mediums, whose internal energy is proportional to some power of the temperature, we find that no engine can achieve the Carnot efficiency at finite power. However, we also find that for the specific example of photonic engines the efficiency at maximal power is larger than the Curzon-Ahlborn efficiency.
- arXiv:2003.11097 [pdf]
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Title: Epitaxial bulk acoustic wave resonators as highly coherent multi-phonon sources for quantum acoustodynamicsAuthors: Vikrant J. Gokhale, Brian P. Downey, D.Scott Katzer, Neeraj Nepal, Andrew C. Lang, Rhonda M. Stroud, David J. MeyerJournal-ref: Nat Commun 11, 2314 (2020)Subjects: Applied Physics (physics.app-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci); Quantum Physics (quant-ph)
Solid-state quantum acoustodynamic (QAD) systems provide a compact platform for quantum information storage and processing by coupling acoustic phonon sources with superconducting or spin qubits. The multi-mode composite high-overtone bulk acoustic wave resonator (HBAR) is a popular phonon source well suited for QAD. However, scattering from defects, grain boundaries, and interfacial/surface roughness in the composite transducer severely limits the phonon relaxation time in sputter-deposited devices. Here, we grow an epitaxial-HBAR, consisting of a metallic NbN bottom electrode and a piezoelectric GaN film on a SiC substrate. The acoustic impedance-matched epi-HBAR has a power injection efficiency > 99% from transducer to phonon cavity. The smooth interfaces and low defect density reduce phonon losses, yielding fxQ products and phonon lifetimes up to 1.36 x 10^17 Hz and 500 microseconds respectively. The GaN/NbN/SiC epi-HBAR is an electrically actuated, multi-mode phonon source that can be directly interfaced with NbN-based superconducting qubits or SiC-based spin qubits.
- arXiv:2003.11111 [pdf, other]
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Title: Robust Gapless Surface State against Surface Magnetic Impurities on (Bi$_{0.5}$Sb$_{0.5}$)$_2$Te$_3$ Evidenced by In Situ Magnetotransport MeasurementsAuthors: Liuqi Yu, Longqian Hu, Jorge L. Barreda, Tong Guan, Xiaoyue He, Kehui Wu, Yongqing Li, Peng XiongJournal-ref: Phys. Rev. Lett. 124 (2020) 126601Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Despite extensive experimental and theoretical efforts, the important issue of the effects of surface magnetic impurities on the topological surface state of a topological insulator (TI) remains unresolved. We elucidate the effects of Cr impurities on epitaxial thin films of (Bi$_{0.5}$Sb$_{0.5}$)$_{2}$Te$_{3}$: Cr adatoms are incrementally deposited onto the TI held in ultrahigh vacuum at low temperatures, and \textit{in situ} magnetoconductivity and Hall effect measurements are performed at each increment with electrostatic gating. In the experimentally identified surface transport regime, the measured minimum electron density shows a non-monotonic evolution with the Cr density ($n_{\mathrm{Cr}}$): it first increases and then decreases with $n_{\mathrm{Cr}}$. This unusual behavior is ascribed to the dual roles of the Cr as ionized impurities and electron donors, having competing effects of enhancing and decreasing the electronic inhomogeneities in the surface state at low and high $n_{\mathrm{Cr}}$ respectively. The magnetoconductivity is obtained for different $n_{\mathrm{Cr}}$ on one and the same sample, which yields clear evidence that the weak antilocalization effect persists and the surface state remains gapless up to the highest $n_{\mathrm{Cr}}$, contrary to the expectation that the deposited Cr should break the time reversal symmetry and induce a gap opening at the Dirac point.
- arXiv:2003.11130 [pdf, other]
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Title: Thermal Hall effect in the pseudogap phase of cupratesAuthors: Chandra M. VarmaSubjects: Strongly Correlated Electrons (cond-mat.str-el)
The conjecture made recently by the group at Sherbrooke, that their observed anomalous thermal Hall effect in the pseudo-gap phase in the cuprates is due to phonons, is supported on the basis of an earlier result that the observed loop-current order in this phase must induce lattice distortions which are linear in the order parameter and an applied magnetic field. The lowered symmetry of the crystal depends on the direction of the field. A consequence is that the elastic constants change proportional to the field and are shown to induce axial thermal transport with the same symmetries as the Lorentz force enforces for the normal electronic Hall effect. Direct measurements of elastic constants in a magnetic field are suggested to verify the quantitative aspects of the results.
- arXiv:2003.11131 [pdf, other]
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Title: How to Split the Electron in HalfAuthors: Gordon W. SemenoffSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); High Energy Physics - Theory (hep-th); Quantum Physics (quant-ph)
This essay is a tribute to Professor Roman Jackiw on the occasion of his eightieth year.
It discusses some ideas about Fermion zero modes and fractional charges and quantum entanglement. - arXiv:2003.11135 [pdf, other]
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Title: Novel color center platforms enabling fundamental scientific discoveryAuthors: Victoria Norman, Sridhar Majety, Zhipan Wang, William H. Casey, Nicholas Curro, Marina RadulaskiSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Optics (physics.optics); Quantum Physics (quant-ph)
Color centers are versatile systems that generate quantum light, sense magnetic fields and produce spin-photon entanglement. We review how these properties have pushed the limits of fundamental knowledge in a variety of scientific disciplines, from rejecting local-realistic theories to sensing superconducting phase transitions. In the light of recent progress in material processing and device fabrication, we identify new opportunities for interdisciplinary fundamental discoveries in physics and geochemistry.
- arXiv:2003.11137 [pdf]
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Title: Nitrogen magneto-ionicsAuthors: Julius de Rojas, Alberto Quintana, Aitor Lopeandía, Joaquín Salguero, Beatriz Muñiz, Fatima Ibrahim, Mairbek Chshiev, Maciej O. Liedke, Maik Butterling, Andreas Wagner, Veronica Sireus, Llibertat Abad, Christopher J. Jensen, Kai Liu, Josep Nogués, José L. Costa-Krämer, Enric Menéndez, Jordi SortComments: 35 pages, 5 main figures, 1 Table, supplementary information includedSubjects: Materials Science (cond-mat.mtrl-sci)
So far, magneto-ionics, understood as voltage-driven ion transport in magnetic materials, has largely relied on controlled migration of oxygen ion/vacancy and, to a lesser extent, lithium and hydrogen. Here, we demonstrate efficient, room-temperature, voltage-driven nitrogen transport (i.e., nitrogen magneto-ionics) by electrolyte-gating of a single CoN film (without an ion-reservoir layer). Nitrogen magneto-ionics in CoN is compared to oxygen magneto-ionics in Co3O4, both layers showing a nanocrystalline face-centered-cubic structure and reversible voltage-driven ON-OFF ferromagnetism. In contrast to oxygen, nitrogen transport occurs uniformly creating a plane-wave-like migration front, without assistance of diffusion channels. Nitrogen magneto-ionics requires lower threshold voltages and exhibits enhanced rates and cyclability. This is due to the lower activation energy for ion diffusion and the lower electronegativity of nitrogen compared to oxygen. These results are appealing for the use of magneto-ionics in nitride semiconductor devices, in applications requiring endurance and moderate speeds of operation, such as brain-inspired computing.
- arXiv:2003.11140 [pdf, other]
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Title: Magnetic Kondo regimes in a frustrated half-filled trimerComments: 14 pages, 9 figuresSubjects: Strongly Correlated Electrons (cond-mat.str-el); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We analyze theoretically the phase diagram of a triangular triple quantum dot with strong onsite repulsion coupled to ferromagnetic leads. This model includes the competition of magnetic ordering of local or itinerant magnetic moments, geometric frustration and Kondo screening. We identify all the phases resulting from this competition. We find that three Kondo phases -- the conventional one, the two-stage underscreened one, and the one resulting from the ferromagnetic Kondo effect -- can be realized at zero temperature, and all are very susceptible to the proximity of ferromagnetic leads. In particular, we find that the quantum dots are spin-polarized in each of these phases. Further, we discuss the fate of the phases at non-zero temperatures, where a plethora of competing energy scales gives rise to complex landscape of crossovers. Each Kondo regime splits into a pair of phases, one not magnetized and one comprising magnetically polarized quantum dots. We discuss our results in the context of heavy-fermion physics in frustrated Kondo lattices.
- arXiv:2003.11144 [pdf, other]
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Title: Fluctuation theorems for multipartite processesAuthors: David H. WolpertComments: 6 pages of text and references, 6 pages of appendices, 1 figureSubjects: Statistical Mechanics (cond-mat.stat-mech); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Many systems are naturally modeled as multiple co-evolving subsystems. In this paper I analyze the stochastic thermodynamics of such systems, formalizing them as multipartite processes. In many multipartite processes the rate matrix of each subsystem $i$ only depends on a proper subset of the remaining subsystems, known as the \textit{community} of $i$. The intersections among the communities of the different subsystems forms a network. Here I derive fluctuation theorems (FTs) for multipartite processes, formulated in terms of this community network. I first derive several \textit{vector} FTs, governing the joint probability of the entropy production (EP) of all of the communities. These vector FTs in turn imply a set of conditional FTs, for the probability of the overall system's EP conditioned on the EP of any single community. Some of these FTs involve extensions of mutual information, to characterize the statistical coupling among the communities induced by the community network.
- arXiv:2003.11146 [pdf, other]
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Title: Thermovoltage in quantum dots with attractive interactionComments: 5 pages, 4 figures. The article has been submitted to "Applied Physics Letters"Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We study the linear and nonlinear thermovoltage of a quantum dot with effective attractive electron-electron interaction and weak, energy-dependent tunnel-coupling to electronic contacts. Remarkably, we find that the thermovoltage shows signatures of repulsive interaction. The characteristics of the thermovoltage get only weakly modified when entering the nonlinear regime of large potential and temperature differences. We expect that the predicted results can be demonstrated in current state-of-the-art experiments. Furthermore, under nonlinear operation, we find extended regions of large power production at efficiencies on the order of the Curzon-Ahlborn bound.
- arXiv:2003.11147 [pdf, ps, other]
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Title: Voltage distribution in a non-locally but globally electroneutral confined electrolyte medium: applications for nanophysiologyComments: 8 figs, 36 poagesSubjects: Soft Condensed Matter (cond-mat.soft); Analysis of PDEs (math.AP); Neurons and Cognition (q-bio.NC)
The distribution of voltage in sub-micron cellular domains remains poorly understood. In neurons, the voltage results from the difference in ionic concentrations which are continuously maintained by pumps and exchangers. However, it not clear how electro-neutrality could be maintained by an excess of fast moving positive ions that should be counter balanced by slow diffusing negatively charged proteins. Using the theory of electro-diffusion, we study here the voltage distribution in a generic domain, which consists of two concentric disks (resp. ball) in two (resp. three) dimensions, where a negative charge is fixed in the inner domain. When global but not local electro-neutrality is maintained, we solve the Poisson-Nernst-Planck equation both analytically and numerically in dimension 1 (flat) and 2 (cylindrical) and found that the voltage changes considerably on a spatial scale which is much larger than the Debye screening length, which assumes electro-neutrality. The present result suggests that long-range voltage drop changes are expected in neuronal microcompartments, probably relevant to explain the activation of far away voltage-gated channels located on the surface.
- arXiv:2003.11153 [pdf]
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Title: The Hidden Fragility of Complex Systems -- Consequences of Change, Changing ConsequencesAuthors: James P. CrutchfieldComments: 11 pages; this http URLJournal-ref: Cultures of Change: Social Atoms and Electronic Lives G. Ascione, C. Massip, J. Perello, editors, ACTAR D Publishers, Barcelona, Spain (2009) 98-111Subjects: Physics and Society (physics.soc-ph); Statistical Mechanics (cond-mat.stat-mech); Adaptation and Self-Organizing Systems (nlin.AO); Chaotic Dynamics (nlin.CD)
Short-term survival and an exuberant plunge into building our future are generating a new kind of unintended consequence -- hidden fragility. This is a direct effect of the sophistication and structural complexity of the socio-technical systems humans create. It is inevitable. And so the challenge is, How much can we understand and predict about these systems and about the social dynamics that lead to their construction?
- arXiv:2003.11158 [pdf, other]
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Title: Phonon-mediated dimensional crossover in bilayer CrI3Authors: M. Rodriguez-Vega, Ze-Xun Lin, A. Leonardo, A. Ernst, G. Chaudhary, M. G. Vergniory, Gregory A. FieteComments: 7 pages, 4 figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
In bilayer CrI3, experimental and theoretical studies suggest that the magnetic order is closely related to the layer staking configuration. In this work, we study the effect of dynamical lattice distortions, induced by non-linear phonon coupling, in the magnetic order of the bilayer system. We use density functional theory to determine the phonon properties and group theory to obtain the allowed phonon-phonon interactions. We find that the bilayer structure possesses low-frequency Raman modes that can be non-linearly activated upon the coherent photo-excitation of a suitable infrared phonon mode. This transient lattice modification, in turn, inverts the sign of the interlayer spin interaction for parameters accessible in experiments, indicating a low-frequency light-induced antiferromagnet-to-ferromagnet transition.
- arXiv:2003.11161 [pdf, other]
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Title: Spin dynamics in the t-t'-J model: Dynamical density-matrix renormalization group studyComments: 7 pages, 5 figuresSubjects: Strongly Correlated Electrons (cond-mat.str-el); Superconductivity (cond-mat.supr-con)
The ground state of a hole-doped t-t'-J ladder with four legs favors a striped charge distribution. Spin excitation from the striped ground state is known to exhibit incommensurate spin excitation near q=(pi,pi) forming an hourglass behavior along the leg direction (qx direction). However, an outward dispersion from the incommensurate position toward q=(0,pi) is strong in intensity, inconsistent with inelastic neutron scattering (INS) experiment. To clarify the origin of this inconsistency, we investigate the dynamical spin structure factor of n-leg t-t'-J ladder by using the dynamical density matrix renormalization group. With increasing n=4 to n=8, we find that the outward dispersion becomes weaker accompanied with weakening of stripe order in the ground state. In addition, excitation energy at q=(pi,pi) decreases with increasing n. The n=8 results are closer to INS data in hole-doped cuprates than the n=4 case. For understanding an direction dependent spin excitation reported by recent resonant inelastic x-ray scattering (RIXS) for cuprate superconductors, we also examine an 8x8 t-t'-J square lattice and obtain a consistent result with RIXS.
- arXiv:2003.11162 [pdf, other]
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Title: Local force method for the ab initio tight-binding model with spin-dependent hoppingComments: 10 pages, 3 figuresSubjects: Strongly Correlated Electrons (cond-mat.str-el); Materials Science (cond-mat.mtrl-sci)
To estimate the Curie temperature of metallic magnets from first principles, we develop a local force method for the tight-binding model having spin-dependent hopping derived from spin density functional theory. While spin-dependent hopping is crucial for the self-consistent mapping to the effective spin model, the numerical cost to treat such non-local terms in the conventional Green's function scheme is formidably expensive. Here, we propose a formalism based on the kernel polynomial method (KPM), which makes the calculation dramatically efficient. We perform a benchmark calculation for bcc-Fe, fcc-Co, and fcc-Ni and find that the effect of the magnetic non-local terms is particularly prominent for bcc-Fe. We also present several local approximations to the magnetic non-local terms for which we can apply the Green's function method and reduce the numerical cost further by exploiting the intermediate representation of the Green's function. By comparing the results of the KPM and local methods, we discuss which local method works most successfully. Our approach provides an efficient way to estimate the Curie temperature of metallic magnets with a complex spin configuration.
- arXiv:2003.11167 [pdf, other]
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Title: Dynamically-enhanced strain in atomically thin resonatorsAuthors: Xin Zhang, Kevin Makles, Léo Colombier, Dominik Metten, Hicham Majjad, Pierre Verlot, Stéphane BerciaudComments: Main manuscript (figures 1 to 4) and SI file (supplementary figures S1 to S20; supplementary sections S1 to S10)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci)
Owing to their low mass and outstanding mechanical figures of merit, graphene and related two-dimensional (2D) materials are ideal building blocks for nano-electro-mechanical systems. At the same time, 2D materials are endowed with unique electronic, optical and phononic properties, suitable for hybrid systems that couple their elementary excitations (excitons, phonons) and/or degrees of freedom (spin, valley) to macroscopic flexural vibrations. The built-in nature of such hybrid systems may yield enhanced strain-mediated coupling as compared to bulkier hybrid systems, e.g., comprising a single quantum emitter coupled to a nano-mechanical resonator. Here, using micro-Raman scattering spectroscopy on circular drums made from pristine graphene monolayers, we demonstrate dynamical softening of optical phonons induced by the macroscopic flexural motion of graphene. This softening is an unambiguous fingerprint of dynamically-induced tensile strain that reaches values up to $\mathbf{\approx 4 \times 10^{-4}}$ under strong non-linear driving. These anomalously large strains exceed the time-averaged values predicted for harmonic vibrations with the same root mean square (RMS) amplitude by more than one order of magnitude and are proportional to the non-linear frequency shift of the mechanical resonance of the drum. Our work provides an impetus for modelling non-linear dynamics in atomically thin resonators beyond elasticity theory and holds promise for dynamical strain engineering and dynamical strain-mediated control of light-matter interactions, single-photon emission or magnetic order in 2D materials and related heterostructures.
- arXiv:2003.11168 [pdf, other]
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Title: Measurement-based cooling of a nonlinear mechanical resonatorComments: 8 pages, 5 figuresJournal-ref: Phys. Rev. B 101, 245410 (2020)Subjects: Quantum Physics (quant-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We propose two measurement-based schemes to cool a nonlinear mechanical resonator down to energies close to that of its ground state. The protocols rely on projective measurements of a spin degree of freedom, which interacts with the resonator through a Jaynes-Cummings interaction. We show the performance of these cooling schemes, that can be either concatenated -- i.e. built by repeating a sequence of dynamical evolutions followed by projective measurements -- or single-shot. We characterize the performance of both cooling schemes with numerical simulations, and pinpoint the effects of decoherence and noise mechanisms. Due to the ubiquity and experimental relevance of the Jaynes-Cummings model, we argue that our results can be applied in a variety of experimental setups.
- arXiv:2003.11179 [pdf, other]
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Title: Unifying the Percolation and Mean-field Descriptions of the Random Lorentz GasAuthors: Giulio Biroli, Patrick Charbonneau, Eric I. Corwin, Yi Hu, Harukuni Ikeda, Grzegorz Szamel, Francesco ZamponiComments: 9 pages, 4 figuresSubjects: Statistical Mechanics (cond-mat.stat-mech)
The random Lorentz gas (RLG) is a minimal model of both transport in heterogenous media and structural glasses. Yet these two perspectives are fundamentally inconsistent, as the dynamical arrest is continuous in the former and discontinuous in the latter. This hinders our understanding of either, as well as of the RLG itself. By considering an exact solution of the RLG in the infinite-dimensional $d\rightarrow\infty$ limit as well as numerics in $d=2\ldots 20$ we here resolve this paradox. Our results reveal the importance of instantonic corrections, related to rare cage escapes, in unifying glass and percolation physics. This advance suggests a starting point for a first-principle description of hopping processes in structural glasses.
- arXiv:2003.11189 [pdf]
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Title: A Gd@C82-based single molecular electret device with switchable electrical polarizationAuthors: Kangkang Zhang, Cong Wang, Minhao Zhang, Zhanbin Bai, Fangfang Xie, Yuanzhi Tan, Yilv Guo, Kuo-Juei Hu, Lu Cao, Shuai Zhang, Xuecou Tu, Lin Kang, Jian Chen, Peiheng Wu, Xuefeng Wang, Jinlan Wang, Junming Liu, Baigeng Wang, Guanghou Wang, Suyuan Xie, Wei Ji, Su-Fei Shi, M. A. Reed, Fengqi SongSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci); Applied Physics (physics.app-ph)
Single molecular electrets exhibiting single molecule electric polarization switching have been long desired as a platform for extremely small non-volatile storage devices, although it is controversial because of the poor stability of single molecular electric dipoles. Here we study the single molecular device of GdC82, where the encapsulated Gd atom forms a charge center, and we have observed a gate controlled switching behavior between two sets of single electron transport stability diagrams. The switching is operated in a hysteresis loop with a coercive gate field of around 0.5Vnm. Theoretical calculations have assigned the two conductance diagrams to corresponding energy levels of two states that the Gd atom is trapped at two different sites of the C82 cage, which possess two different permanent electrical dipole orientations. The two dipole states are stabilized by the anisotropic energy and separated by a transition energy barrier of 70 meV. Such switching is then accessed to the electric field driven reorientation of individual dipole while overcoming the barriers by the coercive gate field, and demonstrates the creation of a single molecular electret.
- arXiv:2003.11191 [pdf]
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Title: Investigation of plasmonic evolution of atomically size-selected Au clusters by electron energy loss spectrum--from solid state to molecular scaleAuthors: Siqi Lu, Lin Xie, Kang Lai, Runkun Chen, Lu Cao, Kuojuei Hu, Xuefeng Wang, Jinsen Han, Xiangang Wan, Jiaqing He, Jiayu Dai, Jianing Chen, Qing Dai, Zhenlin Wang, Guanghou Wang, Fengqi SongSubjects: Atomic and Molecular Clusters (physics.atm-clus); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Optics (physics.optics)
Versatile quantum modes emerge for plasmon describing the collective oscillations of free electrons in metallic nanoparticles when the particle sizes are greatly reduced. Rather than traditional nanoscale study, the understanding of quantum plasmon desires extremal atomic control of the nanoparticles, calling for size dependent plasmon measurement over a series of nanoparticles with atomically adjustable atom number over several orders of magnitude. Here we report the N dependent plasmonic evolution of atomically size selected gold particles with N= 100 70000 using electron energy loss (EEL) spectroscopy in a scanning transmission electron microscope. The EEL mapping assigns a feature at 2.7 eV as the bulk plasmon and another at 2.4 eV as surface plasmon, which evolution reveals three regimes. When N decreases from 70000 to 887, the bulk plasmon stays unchanged while the surface plasmon exhibits a slight red shift from 2.4 to 2.3 eV. It can be understood by the dominance of classical plasmon physics and electron boundary scattering induced retardation. When N further decreases from 887 to 300, the bulk plasmon disappears totally and the surface plasmon shows a steady blueshift, which indicates that the quantum confinement emerges and modifies the intraband transition. When N 100 300, the plasmon is split to three fine features, which is attributed to superimposed single electron transitions between the quantized molecular like energy level by the time dependent density functional theory calculations. The surface plasmon's excitation ratio has a scaling law with an exponential dependence on N ( N^0.669), essentially the square of the radius. A unified evolution picture from the classical to quantum, molecular plasmon is thus demonstrated.
- arXiv:2003.11193 [pdf]
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Title: Effect of antiferromagnetic coupling at interfaces on magnetic properties of Gd/CoFeTaB multilayersSubjects: Materials Science (cond-mat.mtrl-sci); Applied Physics (physics.app-ph)
In this work, a multilayer structure composed of Gd and CoFeTaB was prepared by magnetron sputtering, and the effect of annealing temperatures on magnetic properties of the multilayer structure are investigated. The existence of interfacial antiferromagnetic coupling in this system was proved by analysis of microstructure, magnetic characteristics, and magnetic resonance characteristics. The preparation of artificial multilayer antiferromagnetic structure with weak stray fields was demonstrated, which provides a shortcut for spintronics application.
- arXiv:2003.11201 [pdf, other]
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Title: Interface Studies of Molecular Beam Epitaxy (MBE) Grown ZnSe-GaAs Heterovalent StructuresSubjects: Materials Science (cond-mat.mtrl-sci)
Comprehensive investigations on ZnSe/GaAs and GaAs/ZnSe interfaces were carried out by photoluminescence (PL) and transmission electron microscopy (TEM), as a part of realizing high quality ZnSe-GaAs (100) hetero-valent structures (HS). The nature of ZnSe/GaAs interface under different surface terminations of GaAs was examined. The ZnSe/Ga-terminated GaAs was found to have a superior optical and microstructural quality, with a chemical interface consisting of a mixture of both the GaAs and ZnSe atomic constituents. For GaAs/ZnSe interface studies, a low-temperature migration enhanced epitaxy (LT-MEE) growth technique was used to grow GaAs layers under the conditions compatible to the growth of ZnSe. Both Ga and As-initialized LT-MEE GaAs/ZnSe interfaces were investigated. A defective transition layer was observed along the As-initialized GaAs/ZnSe interface, which may be attributed to the formation Zn$_3$As$_2$ compound. The correlation between the observed optical as well as structural properties of both the (GaAs/ZnSe and ZnSe/GaAs) interfaces and the growth conditions used in this study are discussed in detail. This study could provide a valuable insight on the interface nature of ZnSe-GaAs HS.
- arXiv:2003.11222 [pdf]
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Title: Establishing the carrier scattering phase diagram for ZrNiSn-based half-Heusler thermoelectric materialsAuthors: Qingyong Ren, Chenguang Fu, Qinyi Qiu, Shengnan Dai, Zheyuan Liu, Takatsugu Masuda, Shinichiro Asai, Masato Hagihara, Sanghyun Lee, Shuki Torri, Takashi Kamiyama, Lunhua He, Xin Tong, Claudia Felser, David J. Singh, Tiejun Zhu, Jiong Yang, Jie MaComments: 21 pages, 5 figuresSubjects: Materials Science (cond-mat.mtrl-sci); Applied Physics (physics.app-ph)
Chemical doping is one of the most important strategies for tuning electrical properties of semiconductors, particularly thermoelectric materials. Generally, the main role of chemical doping lies in optimizing the carrier concentration, but there can potentially be other important effects. Here, we show that chemical doping plays multiple roles for both electron and phonon transport properties in half-Heusler thermoelectric materials. With ZrNiSn-based half-Heusler materials as an example, we use high-quality single and polycrystalline crystals, various probes, including electrical transport measurements, inelastic neutron scattering measurement, and first-principles calculations, to investigate the underlying electron-phonon interaction. We find that chemical doping brings strong screening effects to ionized impurities, grain boundary, and polar optical phonon scattering, but has negligible influence on lattice thermal conductivity. Furthermore, it is possible to establish a carrier scattering phase diagram, which can be used to select reasonable strategies for optimization of the thermoelectric performance.
- arXiv:2003.11239 [pdf, other]
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Title: Design of pseudo-mechanisms and multistable units for mechanical metamaterialsSubjects: Soft Condensed Matter (cond-mat.soft)
Mechanism -- collections of rigid elements coupled by perfect hinges which exhibit a zero-energy motion -- motivate the design of a variety of mechanical metamaterials. We significantly enlarge this design space by considering pseudo-mechanisms, collections of elastically coupled elements that exhibit motions with very low energy costs. We show that their geometric design generally is distinct from those of true mechanisms, thus opening up a large and virtually unexplored design space. We further extend this space by designing building blocks with bistable and tristable energy landscapes, realize these by 3D printing, and show how these form unit cells for multistable metamaterials.
- arXiv:2003.11240 [pdf, other]
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Title: Two-photon driven magnon-pair resonance as a signature for spin-nematic ordersComments: 6+5 pages, 6+1 figuresSubjects: Strongly Correlated Electrons (cond-mat.str-el); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Statistical Mechanics (cond-mat.stat-mech); Quantum Physics (quant-ph)
We theoretically study the nonlinear magnetic resonance driven by intense laser or electromagnetic wave in a fully polarized frustrated magnet near a less-visible spin-nematic ordered phase. In general, both magnons and magnon pairs (two-magnon bound state) appear as the low-energy excitation in the saturated state of spin-nematic magnets. Their excitation energies are usually in terahertz (THz) or gigahertz range. Magnon pairs with angular momentum 2$\hbar$ can be excited by the simultaneous absorption of two photons, and such multi-photon processes occur if the applied THz laser is strong enough. We compute laser-driven magnetic dynamics of a frustrated four-spin system with both magnon ($\hbar$) and magnon-pair (2$\hbar$) like excitations which is a simple mimicry of a macroscopic frustrated magnet with a spin nematic phase. We estimate the required strength of magnetic field of laser for the realization of two photon absorption, taking into account dissipation effects with the Lindblad equation. We show that intense THz laser with ac magnetic field of 0.1-1.0 Tesla is enough to observe magnon-pair resonance.
- arXiv:2003.11244 [pdf, other]
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Title: Tensor Networks: Phase transition phenomena on hyperbolic and fractal geometriesComments: accepted in Acta Physica Slovaca (a review based on Jozef Genzor's PhD thesis)Journal-ref: Acta Physica Slovaca 67, 85-206 (2017)Subjects: Statistical Mechanics (cond-mat.stat-mech)
One of the challenging problems in the condensed matter physics is to understand the quantum many-body systems, especially, their physical mechanisms behind. Since there are only a few complete analytical solutions of these systems, several numerical simulation methods have been proposed in recent years. Amongst all of them, the Tensor Network algorithms have become increasingly popular in recent years, especially for their adaptability to simulate strongly correlated systems. The current work focuses on the generalization of such Tensor-Network-based algorithms, which are sufficiently robust to describe critical phenomena and phase transitions of multistate spin Hamiltonians in the thermodynamic limit. We have chosen two algorithms: the Corner Transfer Matrix Renormalization Group and the Higher-Order Tensor Renormalization Group. This work, based on tensor-network analysis, opens doors for the understanding of phase transition and entanglement of the interacting systems on the non-Euclidean geometries. We focus on three main topics: A new thermodynamic model of social influence, free energy is analyzed to classify the phase transitions on an infinite set of the negatively curved geometries where a relation between the free energy and the Gaussian radius of the curvature is conjectured, a unique tensor-based algorithm is proposed to study the phase transition on fractal structures.
- arXiv:2003.11245 [pdf, other]
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Title: New Microscopic Magnetic Hamiltonian for Exotic Spin Textures in MetalsComments: A sign mistake in the derivation is corrected in the 2nd version. Figures have been updatedSubjects: Strongly Correlated Electrons (cond-mat.str-el)
We derive a new microscopic spin Hamiltonian for Rashba-coupled double exchange metals. The Hamiltonian consists of anisotropic interactions of the Dzyaloshinskii-Moriya (DM) and Kitaev form, in addition to the standard isotropic term. We validate the spin Hamiltonian by comparing results with those on the exact spin-fermion model, and present its phase diagram using large scale Monte Carlo simulations. In addition to ferromagnetic, planar spiral and flux states, the model hosts skyrmion crystal and classical spin-liquid states characterized, respectively, by multiple peaks and a diffuse ring pattern in the spin structure factor. The filamentary domain wall structures in the spin-liquid state are in remarkable agreement with experimental data on thin films of MnSi-type B20 metals and transition metals and their alloys.
- arXiv:2003.11250 [pdf]
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Title: Experimental demonstration of random walk by probability chaos using single photonsJournal-ref: Applied Physics Express 13, 042006 (2020)Subjects: Optics (physics.optics); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
In our former work (Sci. Rep. 4: 6039, 2014), we theoretically and numerically demonstrated that chaotic oscillation can be induced in a nanoscale system consisting of quantum dots between which energy transfer occurs via optical near-field interactions. Furthermore, in addition to the nanoscale implementation of oscillators, it is intriguing that the chaotic behavior is associated with probability derived via a density matrix formalism. Indeed, in our previous work (Sci. Rep. 6: 38634, 2016) we examined such oscillating probabilities via diffusivity analysis by constructing random walkers driven by chaotically driven bias. In this study, we experimentally implemented the concept of probability chaos using a single-photon source that was chaotically modulated by an external electro-optical modulator that directly yielded random walkers via single-photon observations after a polarization beam splitter. An evident signature was observed in the resulting ensemble average of the time-averaged mean square displacement. Although the experiment involved a scaled-up, proof-of-concept model of a genuine nanoscale oscillator, the experimental observations clearly validate the concept of oscillating probability, paving the way toward future ideal nanoscale systems.
- arXiv:2003.11251 [pdf, other]
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Title: Efficient generation of extreme terahertz harmonics in 3D Dirac semimetalsComments: 10 pages, 3 figuresSubjects: Optics (physics.optics); Other Condensed Matter (cond-mat.other)
Frequency multiplication of terahertz signals on a solid state platform is highly sought-after for the next generation of high-speed electronics and the creation of frequency combs. Solutions to efficiently generate extreme harmonics (up to the $31^{\rm{st}}$ harmonic and beyond) of a terahertz signal with modest input intensities, however, remain elusive. Using fully nonperturbative simulations and complementary analytical theory, we show that 3D Dirac semimetals (DSMs) have enormous potential as compact sources of extreme terahertz harmonics, achieving energy conversion efficiencies beyond $10^{-5}$ at the $31^{\rm{st}}$ harmonic with input intensities on the order of $10$ MW/cm$^2$, over $10^5$ times lower than in conventional THz high harmonic generation systems. Our theory also reveals a fundamental feature in the nonlinear optics of 3D DSMs: a distinctive regime where higher-order optical nonlinearity vanishes, arising as a direct result of the extra dimensionality in 3D DSMs compared to 2D DSMs. Our findings should pave the way to the development of efficient platforms for high-frequency terahertz light sources and optoelectronics based on 3D DSMs.
- arXiv:2003.11271 [pdf, other]
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Title: Multiple-gap response of type-I noncentrosymmetric BeAu superconductorAuthors: Rustem Khasanov, Ritu Gupta, Debarchan Das, Alfred Amon, Andreas Leithe-Jasper, Eteri SvanidzeComments: 6 pages, 2 figuresJournal-ref: Phys. Rev. Research 2, 023142 (2020)Subjects: Superconductivity (cond-mat.supr-con)
Precise measurements of the thermodynamic critical field ($B_{\rm c}$) in type-I noncentrosymmetric superconductor BeAu were performed by means of the muon-spin rotation/relaxation technique. The temperature evolution of $B_{\rm c}$ can not be described within the single gap scenario and it requires the presence of at least two different types of the superconducting order parameters. The self-consistent two-gap approach, adapted for analysis of $B_{\rm c}(T)$ behavior, suggests the presence of two superconducing energy gaps with the gap to $T_{\rm c}$ ratios $2\Delta/k_{\rm B}T_{\rm c}\simeq4.52$ and $\simeq2.37$ for the big and the small gap, respectively. This implies that the superconductivity in BeAu is unconventional and that the supercarrier pairing occurs at various energy bands.
- arXiv:2003.11276 [pdf, other]
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Title: Geometric effect on near-field heat transfer analysis using efficient graphene and nanotube modelsComments: 7 pages, 9 figuresSubjects: Computational Physics (physics.comp-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Following the recent research enthusiasm on the effect of geometry on near-field heat transfer (NFHT) enhancement, we present an analysis based on simplified yet highly efficient graphene and nanotube models. Two geometries are considered: that of two parallel infinite "graphene" surfaces and that of a one-dimensional infinite "nanotube" line in parallel with an infinite surface. Due to its symmetry, the former is in principal simpler to analyze and even so, earlier works suggested that the application of a full model in this problem still demands heavy computations. Among other findings, our simplified computation - having successfully replicated the results of relevant earlier works - suggests a sharper NFHT enhancement dependence on distance for the line-surface system, namely $J\sim d^{-5.1}$ as compared to $J\sim d^{-2.2}$ for the parallel surface. Such comparisons together with applications of our efficient approach would be the important first steps in the attempt to find a general rule describing geometric dependence of NFHT.
- arXiv:2003.11296 [pdf]
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Title: Combinatorial Laser Molecular Beam Epitaxy System Integrated with Specialized Low-temperature Scanning Tunneling MicroscopyAuthors: Ge He, Zhongxu Wei, Zhongpei Feng, Xiaodong Yu, Beiyi Zhu, Li Liu, Kui Jin, Jie Yuan, Qing HuanComments: 20 pages, 8 figuresJournal-ref: Rev. Sci. Instrum. 91.013904 (2020)Subjects: Applied Physics (physics.app-ph); Materials Science (cond-mat.mtrl-sci); Superconductivity (cond-mat.supr-con)
We present a newly developed facility, comprised of a combinatorial laser molecular beam epitaxy system and an in-situ scanning tunneling microscopy (STM). This facility aims at accelerating the materials research in a highly efficient way, by advanced high-throughput film synthesis techniques and subsequent fast characterization of surface morphology and electronic states. Compared with uniform films deposited by conventional methods, the so-called combinatorial thin films will be beneficial to determining the accurate phase diagrams of different materials due to the improved control of parameters such as chemical substitution and sample thickness resulting from a rotarymask method. A specially designed STM working under low-temperature and ultra-high vacuum conditions is optimized for the characterization of combinatorial thin films, in an XY coarse motion range of 15 mm $\times$ 15 mm and with sub-micrometer location precision. The overall configuration as well as some key aspects like sample holder design, scanner head, and sample/tip/target transfer mechanism are described in detail. The performance of the device is demonstrated by synthesizing high-quality superconducting FeSe thin films with gradient thickness, imaging surfaces of highly oriented pyrolytic graphite, Au (111), Bi2Sr2CaCu2O8+{\delta} (BSCCO) and FeSe. In addition, we have also obtained clean noise spectra of tunneling junctions and the superconducting energy gap of BSCCO. The successful manufacturing of such a facility opens a new window for the next generation of equipment designed for experimental materials research.
- arXiv:2003.11310 [pdf, other]
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Title: Entanglement between Distant Macroscopic Mechanical and Spin SystemsAuthors: Rodrigo A. Thomas, Michał Parniak, Christoffer Østfeldt, Chistoffer B. Møller, Christian Bærentsen, Yeghishe Tsaturyan, Albert Schliesser, Jürgen Appel, Emil Zeuthen, Eugene S. PolzikComments: 24 pages, 12 figuresSubjects: Quantum Physics (quant-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Atomic Physics (physics.atom-ph); Optics (physics.optics)
Entanglement is a vital property of multipartite quantum systems, characterised by the inseparability of quantum states of objects regardless of their spatial separation. Generation of entanglement between increasingly macroscopic and disparate systems is an ongoing effort in quantum science which enables hybrid quantum networks, quantum-enhanced sensing, and probing the fundamental limits of quantum theory. The disparity of hybrid systems and the vulnerability of quantum correlations have thus far hampered the generation of macroscopic hybrid entanglement. Here we demonstrate, for the first time, generation of an entangled state between the motion of a macroscopic mechanical oscillator and a collective atomic spin oscillator, as witnessed by an Einstein-Podolsky-Rosen variance below the separability limit, $0.83 \pm 0.02<1$. The mechanical oscillator is a millimeter-size dielectric membrane and the spin oscillator is an ensemble of $10^9$ atoms in a magnetic field. Light propagating through the two spatially separated systems generates entanglement due to the collective spin playing the role of an effective negative-mass reference frame and providing, under ideal circumstances, a backaction-free subspace; in the experiment, quantum backaction is suppressed by 4.6 dB. Our results pave the road towards measurement of motion beyond the standard quantum limits of sensitivity with applications in force, acceleration,and gravitational wave detection, as well as towards teleportation-based protocols in hybrid quantum networks.
- arXiv:2003.11317 [pdf, other]
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Title: Enhanced magnetization of ultrathin NiFe$_2$O$_4$ films on SrTiO$_3$(001) related to cation disorder and anomalous strainComments: 11 pages, 9 figuresSubjects: Materials Science (cond-mat.mtrl-sci)
NiFe$_2$O$_4$ thin films with varying thickness were grown on SrTiO$_3$(001) by reactive molecular beam epitaxy. Soft and hard x-ray photoelectron spectroscopy measurements reveal a homogeneous cation distribution throughout the whole film with stoichiometric Ni:Fe ratios of 1:2 independent of the film thickness. Low energy electron diffraction and high resolution (grazing incidence) x-ray diffraction in addition to x-ray reflectivity experiments were conducted to obtain information of the film surface and bulk structure, respectively. For ultrathin films up to 7.3 nm, lateral tensile and vertical compressive strain is observed, contradicting an adaption at the interface of NiFe$_2$O$_4$ film and substrate lattice. The applied strain is accompanied by an increased lateral defect density, which is decaying for relaxed thicker films and attributed to the growth of lateral grains. Determination of cationic site occupancies in the inverse spinel structure by analysis of site sensitive diffraction peaks reveals low tetrahedral occupancies for thin, strained NiFe$_2$O$_4$ films, resulting in partial presence of deficient rock salt like structures. These structures are assumed to be responsible for the enhanced magnetization of up to $\sim$250\% of the NiFe$_2$O$_4$ bulk magnetization as observed by superconducting quantum interference device magnetometry for ultrathin films below 7.3 nm thickness.
- arXiv:2003.11327 [pdf]
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Title: Zero-field Nernst effect in a ferromagnetic kagome-lattice Weyl-semimetal Co3Sn2S2Authors: Satya N. Guin, Praveen Vir, Yang Zhang, Nitesh Kumar, Sarah J. Watzman, Chenguang Fu, Enke Liu, Kaustuv Manna, Walter Schnelle, Johannes Gooth, Chandra Shekhar, Yan Sun, Claudia FelserJournal-ref: Advanced Materials 2019, 31, 1806622Subjects: Materials Science (cond-mat.mtrl-sci)
The discovery of magnetic topological semimetals recently attracted significant attention in the field of topology and thermoelectrics. In a thermoelectric device based on the Nernst geometry, an external magnet is required as an integral part. We report a zero-field Nernst effect in a newly discovered hard-ferromagnetic kagome-lattice Weyl-semimetal Co3Sn2S2. A maximum Nernst thermopower of 3 microvolt/K at 80 K in zero field is achieved in this magnetic Weyl-semimetal. Our results demonstrate the possibility of application of topological hard magnetic semimetals for low-power thermoelectric devices based on the Nernst effect and are thus valuable for the comprehensive understanding of transport properties in this class of materials.
- arXiv:2003.11332 [pdf]
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Title: Next-Generation Information Technology Systems for Fast Detectors in Electron MicroscopJournal-ref: Handbook on Big Data and Machine Learning in the Physical Sciences, World Scientific, 2020, 83-120Subjects: Distributed, Parallel, and Cluster Computing (cs.DC); Materials Science (cond-mat.mtrl-sci); Performance (cs.PF); Instrumentation and Detectors (physics.ins-det)
The Gatan K2 IS direct electron detector (Gatan Inc., 2018), which was introduced in 2014, marked a watershed moment in the development of cameras for transmission electron microscopy (TEM) (Pan & Czarnik, 2016). Its pixel frequency, i.e. the number of data points (pixels) recorded per second, was two orders of magnitude higher than the fastest cameras available only five years before. Starting from 2009, the data rate of TEM cameras has outpaced the development of network, mass storage and memory bandwidth by almost two orders of magnitude. Consequently, solutions based on personal computers (PCs) that were adequate until then are no longer able to handle the resulting data rates. Instead, tailored high-performance setups are necessary. Similar developments have occurred for advanced X-ray sources such as the European XFEL, requiring special information technology (IT) systems for data handling (Sauter, Hattne, Grosse-Kunstleve, & Echols, 2013) (Fangohr, et al., 2018). Information and detector technology are currently under rapid development and involve disruptive technological innovations. This chapter briefly reviews the technological developments of the past 20 years, presents a snapshot of the current situation at the beginning of 2019 with many practical considerations, and looks forward to future developments.
- arXiv:2003.11335 [pdf, ps, other]
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Title: Kinetic theory and shear viscosity of dense dipolar hard sphere liquidsComments: 6 pages, 5 figuresSubjects: Soft Condensed Matter (cond-mat.soft); Statistical Mechanics (cond-mat.stat-mech)
Transport properties of dense fluids are fundamentally challenging, because the powerful approaches of equilibrium statistical physics cannot be applied. Polar fluids compound this problem, because the long-range interactions preclude the use of a simple effect-diameter approach based solely on hard spheres. Here, we develop a kinetic theory for dipolar hard-sphere fluids that is valid up to high density. We derive a mathematical approximation for the radial distribution function at contact directly from the equation of state, and use it to obtain the shear viscosity. We also perform molecular-dynamics simulations of this system and extract the shear viscosity numerically. The theoretical results compare favorably to the simulations.
- arXiv:2003.11341 [pdf, other]
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Title: Entropy Production in Systems with Spontaneously Broken Time-ReversalComments: 13 pages, 3 figures, to be published in the proceedings of the MPHYS10 meeting, Belgrade, Serbia, September 2019Subjects: Statistical Mechanics (cond-mat.stat-mech); Mathematical Physics (math-ph); Quantum Physics (quant-ph)
We study the entropy production in non-equilibrium quantum systems without dissipation, which is generated exclusively by the spontaneous breaking of time-reversal invariance. Systems which preserve the total energy and particle number and are in contact with two heat reservoirs are analysed. Focussing on point-like interactions, we derive the probability distribution induced by the entropy production operator. We show that all its moments are positive in the zero frequency limit. The analysis covers both Fermi and Bose statistics.
- arXiv:2003.11344 [pdf]
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Title: Tetragonal superstructure of the antiskyrmion hosting Heusler compound Mn1.4PtSnAuthors: Praveen Vir, Nitesh Kumar, Horst Borrmann, Bayardulam Jamijansuren, Guido Kreiner, Chandra Shekhar, Claudia FelserComments: Includes 4 Figures and Supplementary informationJournal-ref: Chem. Mater. 2019, 31, 15, 5876-5880Subjects: Materials Science (cond-mat.mtrl-sci)
Skyrmions in non-centrosymmetric magnets are vortex-like spin arrangements, viewed as potential candidates for information storage devices. The crystal structure and non-collinear magnetic structure together with magnetic and spin-orbit interactions define the symmetry of the Skyrmion structure. We outline the importance of these parameters in the Heusler compound Mn1.4PtSn which hosts antiskyrmions, a vortex-like spin texture related to skyrmions.1 We overcome the challenge of growing large micro-twin-free single crystals of Mn1.4PtSn which has proved to be the bottleneck for realizing bulk skyrmionic/antiskyrmionic states in a compound. The use of 5d-transition metal, platinum, together with manganese as constituents in the Heusler compound such as Mn1.4PtSn is a precondition for the non-collinear magnetic structure. Due to the tetragonal inverse Heusler structure, Mn1.4PtSn exhibits large magneto-crystalline anisotropy and D2d symmetry, which are necessary for antiskyrmions. The superstructure in Mn1.4PtSn is induced by Mn-vacancies which enables a ferromagnetic exchange interaction to occur. Mn1.4PtSn, the first known tetragonal Heusler superstructure compound, opens up a new research direction for properties related to the superstructure in a family containing thousands of compounds.
- arXiv:2003.11357 [pdf, other]
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Title: Heat driven transport in serial double quantum dot devicesAuthors: Sven Dorsch, Artis Svilans, Martin Josefsson, Bahareh Goldozian, Mukesh Kumar, Claes Thelander, Andreas Wacker, Adam BurkeComments: 16 pages, 9 figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Thermally induced transport experiments through nanostructures give access to an exciting regime where fluctuations are relevant, enabling studies of fundamental thermodynamic concepts and the realization of thermal energy harvesters. Serial double quantum dots represent a model system for a quantum mechanical two-level system with high sensitivity to fluctuations. By combining finite bias spectroscopy with heated measurements and detailed modelling we demonstrate the principles of heat driven transport in such systems. Our experimental system consists of a serial double quantum dot formed in an InAs/InP nanowire, which is coupled to two electron reservoirs and a phonon bath. By using a local metallic joule-heater, we reach a regime where the temperatures of both electron reservoirs and the phonon bath differ. We show that for phonon temperatures exceeding the electron temperatures in the reservoirs, phonon-assisted transport enables heat conversion into electrical power. In addition, different temperatures in the electron reservoirs induce currents via the thermoelectric effect. As the interdot coupling decreases, we observe a transition from mainly thermoelectrically driven to predominantly phonon-assisted transport and discuss how via tuning of the interdot tunnel coupling control over the dominant transport mechanism is possible. Consequently, variation of the interdot coupling in the experiment in combination with modelling of our system allows disentangling of the two effects. We further present evidence of sensitivity of phonon-assisted transport to excited states. Our findings highlight that the well-established system of serial double quantum dots offers a versatile platform for studies of fluctuations and fundamental nanothermodynamics and provide the required tools to disentangle and interpret experimental data.
- arXiv:2003.11374 [pdf, other]
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Title: Quantifying efficient information exchange in real network flowsSubjects: Physics and Society (physics.soc-ph); Disordered Systems and Neural Networks (cond-mat.dis-nn); Statistical Mechanics (cond-mat.stat-mech)
Network science enables the effective analysis of real interconnected systems, characterized by a complex interplay between topology and interconnections strength. It is well-known that the topology of a network affects its resilience to failures or attacks, as well as its functions. Exchanging information is crucial for many real systems: the internet, transportation networks and the brain are key examples. Despite the introduction of measures of efficiency to analyze network flows, i.e. topologies characterized by weighted connectivity, here we show that they fail to capture combined information of link existence and link weight. In this letter we propose a physically-grounded estimator of flow efficiency which can be computed for every weighted network, regardless from the scale and nature of weights and from any (missing) metadata. Remarkably, results show that our estimator captures the heterogeneity of flows along with topological differences and its complement information obtained from percolation analysis of several empirical systems, including transportation, trade, migrations, and brain networks. We show that cutting the heaviest connections may increase the average communication efficiency of the system and hence, counterintuively, a sparser network is not necessarily less efficient. Remarkably, our estimator enables the comparison of communication efficiency of networks arising from different fields, without the possible pitfalls deriving from the scale of flow.
- arXiv:2003.11382 [pdf, other]
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Title: Facile deterministic cutting of 2D materials for twistronics using a tapered fibre scalpelAuthors: L.D. Varma Sangani, R.S. Surya Kanthi, Pratap Chandra Adak, Subhajit Sinha, Alisha H. Marchawala, Takashi Taniguchi, Kenji Watanabe, Mandar M. DeshmukhComments: 12+6 pages, 4+5 figures. The videos are available at this https URLSubjects: Applied Physics (physics.app-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We present a quick and reliable method to cut 2D materials for creating 2D twisted heterostructures and devices. We demonstrate the effectiveness of using a tapered fibre scalped for cutting graphene. Electrical transport measurements show evidence of the desired twist between the graphene layers fabricated using our technique. Statistics of the number of successfully twisted stacks made using our method is compared with h-BN assisted tear-and-stack method. Also, our method can be used for twisted stack fabrication of materials that are few nanometers thick. Finally, we demonstrate the versatility of the tapered fibre scalped for other shaping related applications for sensitive 2D materials.
- arXiv:2003.11385 [pdf]
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Title: Acoustic spin-1 Weyl semimetalSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci)
Topological semimetal, hosting spin-1 Weyl point beyond Dirac and Weyl points, has attracted a great deal of attention. However, the spin-1 Weyl semimetal, which possesses exclusively the spin-1 Weyl points in a clean frequency window, without shadowed by any other nodal points, is yet to be discovered. Here, we report for the first time a spin-1 Weyl semimetal in a phononic crystal. Its spin-1 Weyl points, touched by two linear dispersions and an additional flat band, carry monopole charges (-2,0,2) or (2,0,-2) for the three bands from bottom to top, and result in double Fermi arcs existing both between the 1st and 2nd bands, as well as between the 2nd and 3rd bands. We further observe robust propagation against the multiple joints and topological negative refraction of acoustic surface arc wave. Our results pave the way to explore on the macroscopic scale the exotic properties of the spin-1 Weyl physics.
- arXiv:2003.11408 [pdf, other]
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Title: Parallel dark soliton pair in a bistable 2D exciton-polariton superfluidAuthors: Giovanni Lerario, Sergei V. Koniakhin, Anne Maître, Dmitry Solnyshkov, Alessandro Zilio, Quentin Glorieux, Guillaume Malpuech, Elisabeth Giacobino, Simon Pigeon, Alberto BramatiSubjects: Quantum Gases (cond-mat.quant-gas); Quantum Physics (quant-ph)
Collective excitations, such as vortex-antivortex and dark solitons, are among the most fascinating effects of macroscopic quantum states. However, 2D dark solitons are unstable and collapse into vortices due to snake instabilities. Making use of the optical bistability in exciton-polariton microcavities, we demonstrate that a pair of dark solitons can be formed in the wake of an obstacle in a polariton flow resonantly supported by a homogeneous laser beam. Unlike the purely dissipative case where the solitons are grey and spatially separate, here the two solitons are fully dark, rapidly align at a specific separation distance and propagate parallel as long as the flow is in the bistable regime. Remarkably, the use of this regime allows to avoid the phase fixing arising in resonant pumping regime and to circumvent the polariton decay. Our work opens very wide perspectives of studying new classes of phase-density defects which can form in driven-dissipative quantum fluids of light.
- arXiv:2003.11421 [pdf, other]
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Title: Nonadiabatic charge pumping across two superconductors connected through a normal metal region by periodically driven potentialsComments: 9 pages, 9 figures. Published versionSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Periodically driven systems exhibit resonance when the difference between an excited state energy and the ground state energy is an integer multiple of $\hbar$ times the driving frequency. On the other hand, when a superconducting phase difference is maintained between two superconductors, subgap states appear which carry a Josephson current. A driven Josephson junction therefore opens up an interesting avenue where the excitations due to applied driving affect the current flowing from one superconductor to the other. Motivated by this, we study charge transport in a superconductor-normal metal-superconductor (SNS) junction where oscillating potentials are applied to the normal metal region. We find that for small amplitudes of the oscillating potential, driving at one site reverses the direction of current at the superconducting phase differences when difference between the subgap eigenenergies of the undriven Hamiltonian is integer multiple of $\hbar$ times the driving frequency. For larger amplitudes of oscillating potential, driving at one site exhibits richer features. We show that even when the two superconductors are maintained at same superconducting phase, a current can be driven by applying oscillating potentials to two sites in the normal metal differing by a phase. We find that when there is a nonzero Josephson current in the undriven system, the local peaks and valleys in current of the system driven with an amplitude of oscillating potential smaller than the superconducting gap indicates sharp excitations in the system. In the adiabatic limit, we find that charge transferred in one time period diverges as a powerlaw with pumping frequency when a Josephson current flows in the undriven system. Our calculations are exact and can be applied to finite systems. We discuss possible experimental setups where our predictions can be tested.
- arXiv:2003.11425 [pdf, other]
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Title: Scrambling and decoding the charged quantum informationAuthors: Junyu LiuComments: 62 pages, many figures, theorems and remarks. v2: mainly correct errors and typosSubjects: Quantum Physics (quant-ph); Disordered Systems and Neural Networks (cond-mat.dis-nn); High Energy Physics - Theory (hep-th)
Some deep conjectures about quantum gravity are closely related to the role of symmetries in the gravitational background, especially for quantum black holes. In this paper, we systematically study the theory of quantum information for a charged, chaotic system. We show how the quantum information in the whole system has been represented by its charge sectors, using the theory of quantum chaos and quantum error correction, with concrete examples in the context of complex SYK model. We discuss possible implications for black hole thought experiments and conjectures about quantum gravity in the dynamical setup. We believe this work will have potential applications from theories of quantum gravity to quantum simulation in quantum devices.
- arXiv:2003.11429 [pdf, other]
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Title: Electro-elastic Lamb waves in dielectric platesSubjects: Soft Condensed Matter (cond-mat.soft); Classical Physics (physics.class-ph)
We study the propagation of Lamb waves in soft dielectric plates subject to mechanical and electrical loadings. We find explicit expressions for the dispersion equations in the cases of neo-Hookean and Gent dielectrics. We elucidate the effects of the electric field, of the thickness-to-wavelength ratio, of pre-stress and of strain-stiffening on the wave characteristics.
- arXiv:2003.11436 [pdf]
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Title: Synergistically creating sulfur vacancies in semimetal-supported amorphous MoS2 for efficient hydrogen evolutionAuthors: Guowei Li, Chenguang Fu, Jiquan Wu, Jiancun Rao, Sz-Chian Liou, Xijin Xu, Baiqi Shao, Kai Liu, Enke Liu, Nitesh Kumar, Xianjie Liu, Mats Fahlman, Johannes Gooth, Gudrun Auffermann, Yan Sun, Claudia Felser, Baomin ZhangSubjects: Materials Science (cond-mat.mtrl-sci)
The presence of elemental vacancies in materials is inevitable according to statistical thermodynamics, which will decide the chemical and physical properties of the investigated system. However, the controlled manipulation of vacancies for specific applications is a challenge. Here we report a facile method for creating large concentrations of S vacancies in the inert basal plane of MoS2 supported on semimetal CoMoP2. With a small applied potential, S atoms can be removed in the form of H2S due to the optimized free energy of formation. The existence of vacancies favors electron injection from the electrode to the active site by decreasing the contact resistance. As a consequence, the activity is increased by 221 % with the vacancy-rich MoS2 as electrocatalyst for hydrogen evolution reaction (HER). A small overpotential of 75 mV is needed to deliver a current density of 10 mA cm-2, which is considered among the best values achieved for MoS2. It is envisaged that this work may provide a new strategy for utilizing the semimetal phase for structuring MoS2 into a multi-functional material.
- arXiv:2003.11439 [pdf]
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Title: In situ modification of delafossite type PdCoO2 bulk single crystal for reversible hydrogen sorption and fast hydrogen evolutionAuthors: Guowei Li, Seunghyun Khim, Celesta S. Chang, Chenguang Fu, Nabhanila Nandi, Fan Li, Qun Yang, Graeme R. Blake, Stuart Parkin, Gudrun Auffermann, Yan Sun, David A. Muller, Andrew P. Mackenzie, Claudia FelserSubjects: Materials Science (cond-mat.mtrl-sci)
The observation of extraordinarily high conductivity in delafossite-type PdCoO2 is of great current interest, and there is some evidence that electrons behave like a fluid when flowing in bulk crystals of PdCoO2. Thus, this material is an ideal platform for the study of the electron transfer processes in heterogeneous reactions. Here, we report the use of bulk single crystal PdCoO2 as a promising electrocatalyst for hydrogen evolution reactions (HERs). An overpotential of only 31 mV results in a current density of 10 mA cm^(-2), accompanied by high long-term stability. We have precisely determined that the crystal surface structure is modified after electrochemical activation with the formation of strained Pd nanoclusters in the surface layer. These nanoclusters exhibit reversible hydrogen sorption and desorption, creating more active sites for hydrogen access. The bulk PdCoO2 single crystal with ultra-high conductivity, which acts as a natural substrate for the Pd nanoclusters, provides a high-speed channel for electron transfer
- arXiv:2003.11444 [pdf, other]
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Title: Rigid platform for applying large tunable strains to mechanically delicate samplesAuthors: Joonbum Park, Jack M. Bartlett, Hilary M. L. Noad, Alexander Stern, Mark E. Barber, Markus König, Suguru Hosoi, Takasada Shibauchi, Andrew P. Mackenzie, Alexander Steppke, Clifford W. HicksComments: 11 pages, 9 figuresSubjects: Applied Physics (physics.app-ph); Materials Science (cond-mat.mtrl-sci)
Response to uniaxial stress has become a major probe of electronic materials. Tuneable uniaxial stress may be applied using piezoelectric actuators, and so far two methods have been developed to couple samples to actuators. In one, actuators apply force along the length of a free, beam-like sample, allowing very large strains to be achieved. In the other, samples are affixed directly to piezoelectric actuators, allowing study of mechanically delicate materials. Here, we describe an approach that merges the two: thin samples are affixed to a substrate, that is then pressurized uniaxially using piezoelectric actuators. Using this approach, we demonstrate application of large elastic strains to mechanically delicate samples: the van der Waals-bonded material FeSe, and a sample of CeAuSb$_2$ that was shaped with a focused ion beam.
- arXiv:2003.11453 [pdf, other]
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Title: Symmetry resolved entanglement in two-dimensional systems via dimensional reductionComments: 42 pages, 20 figures, Corrected formulas in Section 3 compared to the first versionSubjects: Statistical Mechanics (cond-mat.stat-mech); High Energy Physics - Theory (hep-th); Quantum Physics (quant-ph)
We report on the calculation of the symmetry resolved entanglement entropies in two-dimensional many-body systems of free bosons and fermions by \emph{dimensional reduction}. When the subsystem is translational invariant in a transverse direction, this strategy allows us to reduce the initial two-dimensional problem into decoupled one-dimensional ones in a mixed space-momentum representation. While the idea straightforwardly applies to any dimension $d$, here we focus on the case $d=2$ and derive explicit expressions for two lattice models possessing a $U(1)$ symmetry, i.e., free non-relativistic massless fermions and free complex (massive and massless) bosons. Although our focus is on symmetry resolved entropies, some results for the total entanglement are also new. Our derivation gives a transparent understanding of the well known different behaviours between massless bosons and fermions in $d\geq2$: massless fermions presents logarithmic violation of the area which instead strictly hold for bosons, even massless. This is true both for the total and the symmetry resolved entropies. Interestingly, we find that the equipartition of entanglement into different symmetry sectors holds also in two dimensions at leading order in subsystem size; we identify for both systems the first term breaking it. All our findings are quantitatively tested against exact numerical calculations in lattice models for both bosons and fermions.
- arXiv:2003.11463 [pdf]
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Title: Charge density wave and superconductivity in the family of telluride chalcogenides Zn1-xCuxIr2-yN(N = Al, Ti, Rh)yTe4Authors: Dong Yan, Yijie Zeng, Yishi Lin, Lingyong Zeng, Junjie Yin, Yuan He, Mebrouka Boubeche, Meng Wang, Yihua Wang, Dao-Xin Yao, Huixia LuoComments: 25 pages, 10 figures, 1 table. arXiv admin note: text overlap with arXiv:1908.09292Subjects: Superconductivity (cond-mat.supr-con); Strongly Correlated Electrons (cond-mat.str-el)
The interplay between superconductivity and charge density wave (CDW)/metal-to-insulator transition (MIT) has long been interested and studied in condensed matter physics. Here we study systematically the charge density wave and superconductivity properties in the solid solutions Zn1-xCuxIr2-yN(N = Al, Ti, Rh)yTe4. Resistivity, magnetic susceptibility and specific heat measurements indicate that the CDW state was suppressed immediately while the superconducting critical temperature (Tc) differs from each system. In the Al- and Ti-substitution cases, Tc increase as y increases and reaches a maximum around 2.75 K and 2.84 K respectively at y = 0.075, followed by a decrease of Tc before the chemical phase boundary is reached at y = 0.2. Nevertheless, Tc decreases monotonously with Rh-doping content y increases and disappears above 0.3 with measuring temperature down to 2 K. Surprisingly, in the Zn1-xCuxIr2Te4 solid solution, Tc enhances as x increases and reaches a maximum value of 2.82 K for x = 0.5 but subsequently survives over the whole doping range of 0.00 - 0.9 despite Tc changes slightly with higher doping content, which differs from the observation of zinc doping suppressing the superconductivity quickly in the high Tc cuprate superconductors. The specific heat anomaly at the superconducting transitions for the representative optimal doping samples are all slightly higher than the BCS value of 1.43 and indicate bulk superconductivity in these compounds. Finally, the CDW transition temperature (TCDW) and superconducting transition temperature (Tc) vs. x/y content phase diagrams of Zn1-xCuxIr2-yN(N = Al, Ti, Rh)yTe4 have been established and compared, which offers good opportunity to study the competition between CDW and superconductivity in the telluride chalcogenides.
- arXiv:2003.11479 [pdf]
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Title: Pressure induced metallization and possible unconventional superconductivity in spin liquid $NaYbSe_{2}$Authors: Zheng Zhang, Yunyu Yin, Xiaoli Ma, Weiwei Liu, Jianshu Li, Feng Jin, Jianting Ji, Yimeng Wang, Xiaoqun Wang, Xiaohui Yu, Qingming ZhangComments: 15 pages, 5 figuresSubjects: Superconductivity (cond-mat.supr-con); Materials Science (cond-mat.mtrl-sci); Strongly Correlated Electrons (cond-mat.str-el)
Beyond the conventional electron pairing mediated by phonons, high-temperature superconductivity in cuprates is believed to stem from quantum spin liquid (QSL). The unconventional superconductivity by doping a spin liquid/Mott insulator, is a long-sought goal but a principal challenge in condensed matter physics because of the lack of an ideal QSL platform. Here we report the pressure induced metallization and possible unconventional superconductivity in $NaYbSe_{2}$, which belongs to a large and ideal family of triangular lattice spin liquid we revealed recently and is evidenced to possess a QSL ground state. The charge gap of NaYbSe2 is gradually reduced by applying pressures, and at ~20 GPa the crystal jumps into a superconducting (SC) phase with Tc ~ 5.8 K even before the insulating gap is completely closed. The metallization is confirmed by further high-pressure experiments but the sign of superconductivity is not well repeated. No symmetry breaking accompanies the SC transition, as indicated by X-ray diffraction and low-temperature Raman experiments under high pressures. This intrinsically connects QSL and SC phases, and suggests an unconventional superconductivity developed from QSL. We further observed the magnetic-field-tuned superconductor-insulator transition which is analogous to that found in the underdoped cuprate superconductor $La_{2-x}Sr_{x}CuO_{4}$. The study is expected to inspire interest in exploring new types of superconductors and sheds light into the intriguing physics from a spin liquid/Mott insulator to a superconductor.
- arXiv:2003.11488 [pdf, other]
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Title: Anisotropic effect of a magnetic field on the neutron spin resonance in FeSeAuthors: Tong Chen, Youzhe Chen, David W. Tam, Bin Gao, Yiming Qiu, Astrid Schneidewind, Igor Radelytskyi, Karel Prokes, Songxue Chi, Masaaki Matsuda, Collin Broholm, Pengcheng DaiComments: To be published as a Rapid Communication in Physical Review BSubjects: Strongly Correlated Electrons (cond-mat.str-el)
We use inelastic neutron scattering to study the effect of a magnetic field on the neutron spin resonance (Er = 3.6 meV) of superconducting FeSe (Tc = 9 K). While a field aligned along the in-plane direction broadens and suppresses the resonance, a c-axis aligned field does so much more efficiently, consistent with the anisotropic field-induced suppression of the superfluid density from the heat capacity measurements. These results suggest that the resonance in FeSe is associated with the superconducting electrons arising from orbital selective quasi-particle excitations between the hole and electron Fermi surfaces.
- arXiv:2003.11503 [pdf, other]
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Title: Non-equilibrium phenomena in superconductors probed by femtosecond time-domain spectroscopyAuthors: Jure DemsarComments: Brief review, submitted to J. Low Temperature Physics, 14 figuresSubjects: Superconductivity (cond-mat.supr-con); Strongly Correlated Electrons (cond-mat.str-el)
Development of ultrafast lasers and non-linear optical techniques over the last two decades provides tools to access real-time dynamics of low energy excitations in superconductors. For example, time-resolved THz spectroscopy and time- and angular-resolved photoemission spectroscopy provide access to the real-time dynamics of the superconducting gap amplitude. Such studies enable determination of microscopic parameters like quasi-particle recombination rates, pair-breaking rates and electron-boson coupling constants. Recently, intense THz pulses have been used to probe the non-linear dynamics, including observation of collective modes. Moreover, using low frequency electromagnetic pulses, there are several reports of amplification of superconductivity in both conventional and unconventional superconductors. Starting with a brief historical overview of the pioneering work, where non-equilibrium phenomena in superconductors were investigated using quasi-continuous excitation, we review some of the insights that are provided by using real-time approaches. We focus on conventional BCS superconductors, whose ground state is reasonably well understood, and address similarities and open questions related to the corresponding studies in high-T$_{c}$ superconductors.
- arXiv:2003.11505 [pdf, other]
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Title: A deep learning approach for determining the chiral indices of carbon nanotubes from high-resolution transmission electron microscopy imagesAuthors: G. D. Förster, A. Castan, A. Loiseau, J. Nelayah, D. Alloyeau, F. Fossard, C. Bichara, H. AmaraComments: for use of the discussed computer code, please contact the corresponding authorSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Computational Physics (physics.comp-ph)
Chiral indices determine important properties of carbon nanotubes (CNTs). Unfortunately, their determination from high-resolution transmission electron microscopy (HRTEM) images, the most accurate method for assigning chirality, is a tedious task. We develop a Convolutional Neural Network that automatizes this process. A large and realistic training data set of CNT images is obtained by means of atomistic computer simulations coupled with the multi-slice approach for image generation. In most cases, results of the automated assignment are in excellent agreement with manual classification, and the origin of failures is identified. The current approach, which combines HRTEM imaging and deep learning algorithms allows the analysis of a statistically significant number of HRTEM images of carbon nanotubes, paving the way for robust estimates of experimental chiral distributions.
- arXiv:2003.11532 [pdf, other]
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Title: Managing Flow of Liquid LightComments: 5 pages, 4 figuresSubjects: Quantum Gases (cond-mat.quant-gas); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Pattern Formation and Solitons (nlin.PS); Optics (physics.optics)
Strongly coupled light-matter systems can carry information over long distances and realize low threshold polariton lasing, condensation and superfluidity. These systems are highly non-equilibrium in nature, so constant nonzero fluxes manifest themselves even at the steady state and set by a complicated interplay between nonlinearity, dispersion, pumping, dissipation and interactions between the various constituents of the system. Predicting the flow velocities even for a simple drive configuration has been challenging and no analytical spatially nonuniform solutions to the system were previously known. Based on the mean-field governing equations of lasers or polariton condensates, we develop a theoretical approach for engineering and controlling the velocity profiles by manipulating the spatial pumping and dissipation in the system. We present analytically exact pumping and dissipation profiles that lead to a large variety of spatially periodic density and velocity profiles. Our approach opens the way to the controllable implementation of laser or polariton flows for ultra-fast information processing and integrated circuits.
Replacements
- arXiv:1312.2600 (replaced) [pdf, ps, other]
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Title: KPZ line ensembleComments: 96 pages, 11 figures. This version corrects a mistake in the proof of Lemma 7.3 and several typographical errors. The authors are grateful to Xuan Wu for pointing out many of these problems. The revision also notes two minor factors missing previously in Definition 3.5 whose presence was revealed by Mihai Nica in his proof [42] of Conjecture 2.18Journal-ref: Probability Theory and Related Fields volume 166, pages 67-185(2016)Subjects: Probability (math.PR); Statistical Mechanics (cond-mat.stat-mech); Mathematical Physics (math-ph)
For each $t\geq 1$ we construct an $\mathbf{N}$-indexed ensemble of random continuous curves with three properties: 1. The lowest indexed curve is distributed as the time $t$ Hopf-Cole solution to the Kardar-Parisi-Zhang (KPZ) stochastic PDE with narrow wedge initial data; 2. The entire ensemble satisfies a resampling invariance which we call the $\mathbf{H}$-Brownian Gibbs property (with $\mathbf{H}(x)=e^{x}$); 3. Increments of the lowest indexed curve, when centered by $-t/24$ and scaled down vertically by $t^{1/3}$ and horizontally by $t^{2/3}$, remain uniformly absolutely continuous (i.e. have tight Radon-Nikodym derivatives) with respect to Brownian bridges as time $t$ goes to infinity.
This construction uses as inputs the diffusion that O'Connell discovered in relation to the O'Connell-Yor semi-discrete Brownian polymer, the convergence result of Nica of the lowest indexed curve of that diffusion to the solution of the KPZ equation with narrow wedge initial data, and the one-point distribution formula proved by Amir-Corwin-Quastel for the solution of the KPZ equation with narrow wedge initial data.
We provide four main applications of this construction: 1. Uniform (as $t$ goes to infinity) Brownian absolute continuity of the time $t$ solution to the KPZ equation with narrow wedge initial data, even when scaled vertically by $t^{1/3}$ and horizontally by $t^{2/3}$; 2. Universality of the $t^{1/3}$ one-point (vertical) fluctuation scale for the solution of the KPZ equation with general initial data; 3. Concentration in the $t^{2/3}$ scale for the endpoint of the continuum directed random polymer; 4.Exponential upper and lower tail bounds for the solution at fixed time of the KPZ equation with general initial data. - arXiv:1604.01641 (replaced) [pdf]
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Title: Anomalous Hall effect in Weyl semimetal half Heusler compounds RPtBi (R = Gd and Nd)Authors: Chandra Shekhar, Nitesh Kumar, V. Grinenko, Sanjay Singh, R. Sarkar, H. Luetkens, Shu-Chun Wu, Yang Zhang, Alexander C. Komarek, Erik Kampert, Yurii Skourski, Jochen Wosnitza, Walter Schnelle, Alix McCollam, Uli Zeitler, Jürgen Kübler, Binghai Yan, H.-H. Klauss, S. S. P. Parkin, C. FelserComments: 24 pages including supplementary informationJournal-ref: PNAS, 115 (2018) 9140-9144Subjects: Materials Science (cond-mat.mtrl-sci)
Topological materials ranging from topological insulators to Weyl and Dirac semimetals form one of the most exciting current fields in condensed-matter research. Many half-Heusler compounds, RPtBi (R= rare earth) have been theoretically predicted to be topological semimetals. Among various topological attributes envisaged in RPtBi, topological surface states, chiral anomaly and planar Hall effect have been observed experimentally. Here, we report on an unusual intrinsic anomalous Hall effect (AHE) in the antiferromagnetic Heusler Weyl semimetal compounds GdPtBi and NdPtBi that is observed over a wide temperature range. In particular, GdPtBi exhibits an anomalous Hall conductivity of up to 60 ohm-1cm-1 and an anomalous Hall angle as large as 23%. Muon spin resonance (mu-SR) studies of GdPtBi indicate a sharp antiferromagnetic transition (T_N) at 9 K without any noticeable magnetic correlations above T_N. Our studies indicate that Weyl points in these half-Heuslers are induced by a magnetic field via exchange-splitting of the electronic bands at or near to the Fermi energy which is the source of the chiral anomaly and the AHE.
- arXiv:1612.01343 (replaced) [pdf]
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Title: Phonon scattering limited mobility in the representative cubic perovskite semiconductors SrGeO$_3$, BaSnO$_3$ and SrTiO$_3$Authors: Christian A. Niedermeier, Yu Kumagai, Keisuke Ide, Takayoshi Katase, Fumiyasu Oba, Hideo Hosono, Toshio KamiyaComments: 28 pages, 9 figuresJournal-ref: Phys. Rev. B 101, 125206 (2020)Subjects: Materials Science (cond-mat.mtrl-sci)
Cubic perovskite oxides are emerging high-mobility transparent conducting oxides (TCOs), but Ge-based TCOs had not been known until the discovery of metastable cubic SrGeO$_3$. $0.5 \times 0.4 \times 0.2$-mm$^3$ large single crystals of the cubic SrGeO$_3$ perovskite were successfully synthesized employing the high-pressure flux method. The phonon spectrum is determined from the IR optical reflectance and Raman-scattering analysis to evaluate the electron transport governed by optical phonon scattering. A calculated room-temperature mobility on the order of $3.9 \times 10^2$ cm$^2$V$^{-1}$s$^{-1}$ is obtained, identifying cubic SrGeO$_3$ as one of the most promising TCOs. Employing classical phonon theory and a combined experimental-theoretical approach, a comprehensive analysis of the intrinsic electron mobility in the cubic perovskite semiconductors SrGeO$_3$, BaSnO$_3$, and SrTiO$_3$ is provided based on the magnitude of polarization and eigenfrequency of optically active phonons.
- arXiv:1705.08871 (replaced) [pdf, other]
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Title: Eliashberg theory with the external pair potentialAuthors: Konstantin V. GrigorishinComments: 12 pages, 3 figuresSubjects: Superconductivity (cond-mat.supr-con)
Based on BCS model with the external pair potential formulated in a work K.V. Grigorishin Phys. Lett. A 381, 3089 (2017), analogous model with electron-phonon coupling and Coulomb coupling is proposed. The generalized Eliashberg equations in the regime of renormalization of the order parameter are obtained. High temperature asymptotics and effect of Coulomb pseudopotential on them are investigated: as in the BCS model the order parameter asymptotically tends to zero as temperature rises, but the accounting of the Coulomb pseudopotential leads to existence of critical temperature. The effective Ginzburg-Landau theory is formulated for such model.
- arXiv:1712.08115 (replaced) [pdf, other]
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Title: Emerging chiral edge states from the confinement of a magnetic Weyl semimetal in Co$_3$Sn$_2$S$_2$Comments: Revised 3rd version of the manuscriptJournal-ref: Phys. Rev. B 101, 115106 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el); Materials Science (cond-mat.mtrl-sci)
The quantum anomalous Hall effect (QAHE) and magnetic Weyl semimetals (WSMs) are topological states induced by intrinsic magnetic moments and spin-orbit coupling. Their similarity suggests the possibility of achieving the QAHE by dimensional confinement of a magnetic WSM along one direction. In this study, we investigate the emergence of the QAHE in the two-dimensional (2D) limit of magnetic WSMs due to finite size effects in thin films and step-edges. We demonstrate the feasibility of this approach with effective models and real materials. To this end, we have chosen the layered magnetic WSM Co$_3$Sn$_2$S$_2$, which features a large anomalous Hall conductivity and anomalous Hall angle in its 3D bulk, as our material candidate. In the 2D limit of Co$_3$Sn$_2$S$_2$ two QAHE states exist depending on the stoichiometry of the 2D layer. One is a semimetal with a Chern number of 6, and the other is an insulator with a Chern number of 3. The latter has a band gap of 0.05 eV, which is much larger than that in magnetically doped topological insulators. Our findings naturally explain the existence of chiral states in step edges of bulk Co$_3$Sn$_2$S$_2$ which habe been reported in a recent experiment at $T = 4K$ and present a realistic avenue to realize QAH states in thin films of magnetic WSMs.
- arXiv:1803.00270 (replaced) [pdf, ps, other]
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Title: Incommensurate Magnetic Ordering from One-Dimensional Correlated Topological Bulk StatesAuthors: J.-G. LussierComments: 5 pagesSubjects: Strongly Correlated Electrons (cond-mat.str-el)
A phenomenological model accounts for the calculation of incommensurate ordering wave vectors (IC) in several Ce- and U-based f-electron itinerant compounds (CePtSn, CePdSn, CeNiSn, CeRhIn$_5$, URu$_2$Si$_2$, CeNiAsO, CeCu$_{(6-x)}$Au$_x$, UNi$_2$Al$_3$, CeCuSn) as well as in BSSCO, Rb$_2$ZnBr$_4$, MnSi and prototypical IC system Chromium metal. This model is justified by a many-body topological one-dimensional (1-D) Dirac Hamiltonian after center of mass transformation on a chiral set of momenta defined by a local expansion of crystallographic Bragg planes. Implications for the emergence of long range bulk states driven by fluctuations with this model are discussed.
- arXiv:1804.08323 (replaced) [pdf, other]
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Title: Asymptotics of even-even correlations in the Ising modelComments: Changed section numbering to match the published versionJournal-ref: Probability Theory and Related Fields 175, 309-340 (2019)Subjects: Probability (math.PR); Statistical Mechanics (cond-mat.stat-mech); Mathematical Physics (math-ph)
We consider finite-range ferromagnetic Ising models on $\mathbb{Z}^d$ in the regime $\beta<\beta_c$. We analyze the behavior of the prefactor to the exponential decay of $\mathrm{Cov}(\sigma_A,\sigma_B)$, for arbitrary finite sets $A$ and $B$ of even cardinality, as the distance between $A$ and $B$ diverges.
- arXiv:1810.06330 (replaced) [pdf, ps, other]
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Title: Flow optimization process in a transportation networkSubjects: Physics and Society (physics.soc-ph); Statistical Mechanics (cond-mat.stat-mech)
Numerous networks, such as transportation, distribution and delivery networks optimize their designs in order to increase efficiency and lower costs, improving the stability of its intended functions, etc. Networks that distribute goods, such as electricity, water, gas, telephone and data (Internet), or services as mail, railways and roads are examples of transportation networks. The optimal design fixes network architecture, including clustering, degree distribution, hierarchy, community structures and other structural metrics. These networks are specifically designed for efficient transportation, minimizing transit times and costs. All sorts of transportation networks face the same problem: traffic congestion among their channels. In this work we considered a transportation network model in which we optimize/minimize a cost function for the flux/current at each channel/link of the network. We performed simulations and an analytical study of this problem, focusing on the fraction of used channels and the flow distribution through these channels. Our results show that, after the initial transient, the fraction of used channels stays constant and, remarkably, this result does not depend on the lattice structure (2D, 3D, or long-range connections). For the case of high flow, all channels in the network are used. On the other hand, in the small flow limit, we observe a novel behavior that the fraction of used channels depends on the square root of the flow.
- arXiv:1812.03310 (replaced) [pdf]
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Title: Chiral Topological Semimetal with Multifold Band Crossings and Long Fermi arcsAuthors: Niels B. M. Schröter, Ding Pei, Maia G. Vergniory, Yan Sun, Kaustuv Manna, Fernando de Juan, Jonas. A. Krieger, Vicky Süss, Marcus Schmidt, Pavel Dudin, Barry Bradlyn, Timur K. Kim, Thorsten Schmitt, Cephise Cacho, Claudia Felser, Vladimir N. Strocov, Yulin ChenComments: Original journal submission date Aug 17th 2018, v2 is the accepted manuscriptJournal-ref: Nature Physics (2019) https://www.nature.com/articles/s41567-019-0511-ySubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Topological semimetals in crystals with a chiral structure (which possess a handedness due to a lack of mirror and inversion symmetries) are expected to display numerous exotic physical phenomena, including fermionic excitations with large topological charge [1], long Fermi arc surface states [2,3], unusual magnetotransport [4] and lattice dynamics [5], as well as a quantized response to circularly polarized light [6]. To date, all experimentally confirmed topological semimetals exist in crystals that contain mirror operations, meaning that these properties do not appear. Here, we show that AlPt is a structurally chiral topological semimetal that hosts new fourfold and sixfold fermions, which can be viewed as a higher spin eneralization of Weyl fermions without equivalence in elementary particle physics. These multifold fermions are located at high symmetry points and have Chern numbers larger than those in Weyl semimetals, thus resulting in multiple Fermi arcs that span the full diagonal of the surface Brillouin zone. By imaging these long Fermi arcs, we experimentally determine the magnitude and sign of their Chern number, allowing us to relate their dispersion to the handedness of their host crystal.
- arXiv:1905.01702 (replaced) [pdf]
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Title: $Z_3$-vestigial nematic order due to superconducting fluctuations in the doped topological insulator Nb$_x$Bi$_2$Se$_3$ and Cu$_x$Bi$_2$Se$_3$Authors: Chang-woo Cho, Junying Shen, Jian Lyu, Omargeldi Atanov, Qianxue Chen, Seng Huat Lee, Yew San Hor, Dariusz Jakub Gawryluk, Ekaterina Pomjakushina, Marek Bartkowiak, Matthias Hecker, Jörg Schmalian, Rolf LortzSubjects: Superconductivity (cond-mat.supr-con)
A state of matter with a multi-component order parameter can give rise to vestigial order. In the vestigial phase, the primary order is only partially melted, leaving a remaining symmetry breaking behind, an effect driven by strong classical or quantum fluctuations. Vestigial states due to primary spin and charge-density-wave order have been discussed in the context of iron-based and cuprate materials. Here we present the observation of a partially melted superconductor in which pairing fluctuations condense at a separate phase transition and form a nematic state with broken Z3, i.e. three-state Potts-model symmetry. High-resolution thermal expansion, specific heat and magnetization measurements of the doped topological insulator NbxBi2Se3 reveal that this symmetry breaking occurs at Tnem=3.8 K above Tc=3.25 K, along with an onset of superconducting fluctuations. Thus, before Cooper pairs establish long-range coherence at Tc, they fluctuate in a way that breaks the rotational invariance at Tnem and induces a distortion of the crystalline lattice. Similar results are found for CuxBi2Se3.
- arXiv:1905.10832 (replaced) [pdf, other]
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Title: How carbon vacancies can affect the properties of group IV color centers in diamond: A study of thermodynamics and kineticsComments: 19 pages, 7 figuresJournal-ref: Journal of Applied Physics 126, 195103 (2019)Subjects: Materials Science (cond-mat.mtrl-sci)
Recently there has been much interest in using Group IV elements from the Periodic Table to fabricate and study X$V$ color centers in diamond where X = Si, Ge, Sn, or Pb and $V$ is a carbon vacancy. These Group IV color centers have a number of interesting spin and optical properties which could potentially make them better candidates than N$V^-$ centers for important applications in quantum computing and quantum information processing. Unfortunately, the very same ion implantation process that is required to create these X$V$ color centers in diamond necessarily also produces many carbon vacancies ($V_{\rm C}$) which can form complexes with these color centers ($V_{\rm C}-$X$V$) that can dramatically affect the properties of the isolated X$V$ color centers. The main focus of this work is to use density-functional theory (DFT) to study the thermodynamics and kinetics of the formation of these $V_{\rm C}-$X$V$ complexes and to suggest experimental ways to impede this process such as varying the Fermi level of the host diamond material through chemical doping or applying an external electrical bias. We also include a discussion of how the simple presence of many $V_{\rm C}$ can negatively impact the spin coherence times ($T_2$) of Group IV color centers through the presence of acoustic phonons.
- arXiv:1906.05576 (replaced) [pdf]
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Title: Bethe-Slater-curve-like behavior and interlayer spin-exchange coupling mechanisms in two-dimensional magnetic bilayersAuthors: Xieyu Zhou, Cong Wang, Linwei Zhou, Yuhao Pan, Zhong-Yi Lu, Xiangang Wan, Xiaoqun Wang, Wei JiSubjects: Materials Science (cond-mat.mtrl-sci)
Layered magnets have recently received tremendous attention, however, spin-exchange coupling mechanism across their interlayer regions is yet to be revealed. Here, we report a Bethe-Slater-curve (BSC) like behavior in nine transition metal dichalcogenide bilayers (MX2, M=V, Cr, Mn; X=S, Se, Te) and established interlayer spin-exchange coupling mechanisms at their van der Waals gaps using first-principle calculations. The BSC-like behavior offers a distance-dependent interlayer anti-ferromagnetic (AFM) to ferromagnetic (FM) transition. This phenomenon is explained with the spin-exchange coupling mechanisms established using bilayer CrSe2 as a prototype in this work. The overlapped interfacial Se wavefunctions form an interlayer effective site, the spin alignment of which determines interlayer magnetic coupling. At a shorter interlayer distance, Pauli repulsion at this site dominates and thus favors anti-parallel oriented spins leading to interlayer AFM. For a longer distance, kinetic energy gain of polarized electrons across the bilayer balances the Pauli repulsion and the bilayer prefers an interlayer FM state. In light of this, the AFM-FM transition is a result of competition between Pauli and Coulomb repulsion and kinetic energy gain. All these results open a new route to tune interlayer magnetism and the revealed spin-exchange coupling mechanisms are a paramount addition to those previously established ones.
- arXiv:1907.04925 (replaced) [pdf, other]
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Title: Maximum Entropy approach to multivariate time series randomizationComments: 15 pages, 6 figures, 2 tablesSubjects: Statistical Finance (q-fin.ST); Statistical Mechanics (cond-mat.stat-mech); Physics and Society (physics.soc-ph)
Natural and social multivariate systems are commonly studied through sets of simultaneous and time-spaced measurements of the observables that drive their dynamics, i.e., through sets of time series. Typically, this is done via hypothesis testing: the statistical properties of the empirical time series are tested against those expected under a suitable null hypothesis. This is a very challenging task in complex interacting systems, where statistical stability is often poor due to lack of stationarity and ergodicity. Here, we describe an unsupervised, data-driven framework to perform hypothesis testing in such situations. This consists of a statistical mechanical approach - analogous to the configuration model for networked systems - for ensembles of time series designed to preserve, on average, some of the statistical properties observed on an empirical set of time series. We showcase its possible applications on a set of stock market returns from the NYSE.
- arXiv:1909.07238 (replaced) [pdf, other]
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Title: An experimental proof that resistance-switching memories are not memristorsSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Emerging Technologies (cs.ET)
It has been suggested that all resistive-switching memory cells are memristors. The latter are hypothetical, ideal devices whose resistance, as originally formulated, depends only on the net charge that traverses them. Recently, an unambiguous test has been proposed [J. Phys. D: Appl. Phys. {\bf 52}, 01LT01 (2019)] to determine whether a given physical system is indeed a memristor or not. Here, we experimentally apply such a test to both in-house fabricated Cu-SiO2 and commercially available electrochemical metallization cells. Our results unambiguously show that electrochemical metallization memory cells are not memristors. Since the particular resistance-switching memories employed in our study share similar features with many other memory cells, our findings refute the claim that all resistance-switching memories are memristors. They also cast doubts on the existence of ideal memristors as actual physical devices that can be fabricated experimentally. Our results then lead us to formulate two memristor impossibility conjectures regarding the impossibility of building a model of physical resistance-switching memories based on the memristor model.
- arXiv:1909.08456 (replaced) [pdf, other]
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Title: Theoretical design of highly correlated electron states in delafossite heterostructuresComments: 8 pages, 8 figuresJournal-ref: Phys. Rev. Research 2, 013352 (2020)Subjects: Materials Science (cond-mat.mtrl-sci); Strongly Correlated Electrons (cond-mat.str-el)
Delafossites represent natural heterostructures which can host rather different electronic characteristics in their constituting layers. The design of novel heterostructure architectures highlighting the competition between such varying layer properties is promising from the viewpoint of basic research as well as for future technological applications. By means of the combination of density functional theory and dynamical mean-field theory, we here unveil the formation of highly correlated electron states in delafossite heterostructures build from metallic PdCrO$_2$ and insulating AgCrO$_2$. Due to the sophisticated coupling between layers of strong and of weak internal electron-electron interaction, correlation-induced semimetals at ambient temperature and doped Mott-insulators at lower temperature are predicted. The unique electronic structure of delafossite heterostructures opens a door to research on novel challenging quantum matter.
- arXiv:1910.05197 (replaced) [pdf, other]
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Title: Bulk topological proximity effect in multilayer systemsComments: Main text: 4 pages, 2 figures. Supplemental material: 4 pages, 2 figuresSubjects: Strongly Correlated Electrons (cond-mat.str-el); Quantum Gases (cond-mat.quant-gas); Quantum Physics (quant-ph)
We investigate the bulk topological proximity effect in multilayer hexagonal lattice systems by which one can introduce topological properties into a system composed of multiple trivial layers by tunnel coupling to a single nontrivial layer described by the Haldane model. This phenomenon depends not only on the number of layers but also on their arrangement, which can lead to the emergence of dark states in multilayer systems. The response of a trivial system to the proximity of a topological insulator appears to be highly nonlocal, in contrast to the proximity effect observed in context of superconductivity. Furthermore, for a wide range of parameters our system is semimetallic with multiple Dirac points emerging in the Brillouin zone.
- arXiv:1910.08459 (replaced) [pdf, other]
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Title: Symmetry resolved entanglement: Exact results in 1D and beyondComments: 29 pages, 7 figures; v2: published versionJournal-ref: J. Stat. Mech. (2020) 033106Subjects: Statistical Mechanics (cond-mat.stat-mech); Quantum Gases (cond-mat.quant-gas); High Energy Physics - Theory (hep-th); Quantum Physics (quant-ph)
In a quantum many-body system that possesses an additive conserved quantity, the entanglement entropy of a subsystem can be resolved into a sum of contributions from different sectors of the subsystem's reduced density matrix, each sector corresponding to a possible value of the conserved quantity. Recent studies have discussed the basic properties of these symmetry-resolved contributions, and calculated them using conformal field theory and numerical methods. In this work we employ the generalized Fisher-Hartwig conjecture to obtain exact results for the characteristic function of the symmetry-resolved entanglement ("flux-resolved entanglement") for certain 1D spin chains, or, equivalently, the 1D fermionic tight binding and the Kitaev chain models. These results are true up to corrections of order $o(L^{-1})$ where $L$ is the subsystem size. We confirm that this calculation is in good agreement with numerical results. For the gapless tight binding chain we report an intriguing periodic structure of the characteristic functions, which nicely extends the structure predicted by conformal field theory. For the Kitaev chain in the topological phase we demonstrate the degeneracy between the even and odd fermion parity sectors of the entanglement spectrum due to virtual Majoranas at the entanglement cut. We also employ the Widom conjecture to obtain the leading behavior of the symmetry-resolved entanglement entropy in higher dimensions for an ungapped free Fermi gas in its ground state.
- arXiv:1910.09967 (replaced) [pdf, other]
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Title: Entanglement entropies of inhomogeneous Luttinger liquidsComments: 19 pages, 4 figuresJournal-ref: J. Phys. A: Math. Theor.53 155001 (2020)Subjects: Statistical Mechanics (cond-mat.stat-mech); Quantum Gases (cond-mat.quant-gas); Strongly Correlated Electrons (cond-mat.str-el)
We develop a general framework to compute the scaling of entanglement entropy in inhomogeneous one-dimensional quantum systems belonging to the Luttinger liquid universality class. While much insight has been gained in homogeneous systems by making use of conformal field theory techniques, our focus is on systems for which the Luttinger parameter $K$ depends on position, and conformal invariance is broken. An important point of our analysis is that contributions stemming from the UV cutoff have to be treated very carefully, since they now depend on position. We show that such terms can be removed either by considering regularized entropies specifically designed to do so, or by tabulating numerically the cutoff, and reconstructing its contribution to the entropy through the local density approximation. We check our method numerically in the spin-1/2 XXZ spin chain in a spatially varying magnetic field, and find excellent agreement.
- arXiv:1910.10072 (replaced) [pdf, other]
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Title: Emergence of the unconventional type-II Nambu-Goldstone modes in Bose superfluidsComments: 5+6 pages, 3 figures; Updates are made according to the referee reportSubjects: Quantum Gases (cond-mat.quant-gas); High Energy Physics - Theory (hep-th); Quantum Physics (quant-ph)
The Nambu-Goldstone (NG) modes in a non-relativistic system can be classified into two types from their characteristic features: being of either an odd (type I) or an even (type II) power energy-momentum dispersion. Conventionally, the type-II NG modes may universally arise from the spontaneous breaking of noncommutative symmetry pairs. Here, we predict a novel type of quadratically dispersed NG modes which emerges from mixed $s$ and $p$ band Bose superfluids in a two-dimensional optical lattice and, unlike the conventional type-II NG modes, cannot be solely interpreted with the celebrated symmetry-based argument. Instead, we show that the existence of such modes is linked to an emergent topological transition on a projection complex order-parameter space, for which a generic framework is established. Our work reveals a new universal mechanism for emergence of type-II NG modes beyond the conventional symmetry-based classification.
- arXiv:1910.14362 (replaced) [pdf, other]
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Title: Optical properties of graphene quantum dots: the role of chiral symmetryJournal-ref: 2D Materials 7 (2020) 025041Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci)
We analyse the electronic and optical properties of graphene quantum dots (GQD) using accurate \textit{ab initio} many-body $GW$ and Bethe-Salpeter calculations. We show that most pristine GQD, including structures with irregular shapes, are characterized by dark low energy singlet excitations that quench fluorescence. We rationalizqe this property by exploiting the chiral symmetry of the low energy electronic states in graphene. Edge \textit{sp}$^3$ functionalization is shown to efficiently brighten these low lying excitations by distorting the \textit{sp}$^2$ backbone planar symmetry. Such findings reveal an original indirect scenario for the influence of functionalization on the photoluminescence properties.
- arXiv:1911.02350 (replaced) [pdf, other]
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Title: Cooperatively enhanced reactivity and 'stabilitaxis' of dissociating oligomeric proteinsComments: Main Text (9 pages, 3 figures) plus Supplementary Information (7 pages, 7 figures)Subjects: Chemical Physics (physics.chem-ph); Soft Condensed Matter (cond-mat.soft); Statistical Mechanics (cond-mat.stat-mech); Biological Physics (physics.bio-ph)
Many functional units in biology, such as enzymes or molecular motors, are composed of several subunits that can reversibly assemble and disassemble. This includes oligomeric proteins composed of several smaller monomers, as well as protein complexes assembled from a few proteins. By studying the generic spatial transport properties of such proteins, we investigate here whether their ability to reversibly associate and dissociate may confer them a functional advantage with respect to non-dissociating proteins. In uniform environments with position-independent association-dissociation, we find that enhanced diffusion in the monomeric state coupled to reassociation into the functional oligomeric form leads to enhanced reactivity with distant targets. In non-uniform environments with position-dependent association-dissociation, caused e.g. by spatial gradients of an inhibiting chemical, we find that dissociating proteins generically tend to accumulate in regions where they are most stable, a process that we term 'stabilitaxis'.
- arXiv:1911.02626 (replaced) [pdf]
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Title: Cloud shape of a molecular Bose-Einstein condensate in a disordered trap: a case study of the dirty boson problemComments: 14 pages, 7 figuresJournal-ref: New J. Phys. 22 (2020) 033021Subjects: Quantum Gases (cond-mat.quant-gas)
We investigate, both experimentally and theoretically, the static geometric properties of a harmonically trapped Bose-Einstein condensate of ${}^6$Li$_2$ molecules in laser speckle potentials. Experimentally, we measure the in-situ column density profiles and the corresponding transverse cloud widths over many laser speckle realizations. We compare the measured widths with a theory that is non-perturbative with respect to the disorder and includes quantum fluctuations. Importantly, for small disorder strengths we find quantitative agreement with the perturbative approach of Huang and Meng, which is based on Bogoliubov theory. For strong disorder our theory perfectly reproduces the geometric mean of the measured transverse widths. However, we also observe a systematic deviation of the individual measured widths from the theoretically predicted ones. In fact, the measured cloud aspect ratio monotonously decreases with increasing disorder strength, while the theory yields a constant ratio. We attribute this discrepancy to the utilized local density approximation, whose possible failure for strong disorder suggests a potential future improvement.
- arXiv:1911.02719 (replaced) [pdf, other]
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Title: Possible instability of one-step replica symmetry breaking in p-spin Ising models outside mean-field theoryComments: 12 pages, 4 figures; A whole new section has been added; A new type of model has been introduced and discussed; Title changed; Published versionJournal-ref: Phys. Rev. E 101, 032127 (2020)Subjects: Disordered Systems and Neural Networks (cond-mat.dis-nn); Statistical Mechanics (cond-mat.stat-mech)
The fully-connected Ising $p$-spin model has for $p >2$ a discontinuous phase transition from the paramagnetic phase to a stable state with one-step replica symmetry breaking (1RSB). However, simulations in three dimension do not look like these mean-field results and have features more like those which would arise with full replica symmetry breaking (FRSB). To help understand how this might come about we have studied in the fully connected $p$-spin model the state of two-step replica symmetry breaking (2RSB). It has a free energy degenerate with that of 1RSB, but the weight of the additional peak in $P(q)$ vanishes. We expect that the state with full replica symmetry breaking (FRSB) is also degenerate with that of 1RSB. We suggest that finite size effects will give a non-vanishing weight to the FRSB features, as also will fluctuations about the mean-field solution. Our conclusion is that outside the fully connected model in the thermodynamic limit, FRSB is to be expected rather than 1RSB.
- arXiv:1911.10085 (replaced) [pdf, other]
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Title: Comprehensive scan for nonmagnetic Weyl semimetals with nonlinear optical responseAuthors: Qiunan Xu, Yang Zhang, Klaus Koepernik, Wujun Shi, Jeroen van den Brink, Claudia Felser, Yan SunJournal-ref: npj Comput. Mater. 6, 32 (2020)Subjects: Materials Science (cond-mat.mtrl-sci); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
As the development of topological band theory, comprehensive databases about time reversal and crystalline symmetries protected nonmagnetic topological materials were developed via first-principles calculations recently. However, owing to the low symmetry requirement of Weyl points, the symmetry-based topological indicator cannot be applied to Weyl semimetals (WSMs). Hitherto, the WSMs with Weyl points in arbitrary positions are still absent in the well-known databases. In this work, we develop an efficient algorithm to search for Weyl points automatically and establish a database of nonmagnetic WSMs with Weyl points near Fermi level based on the total experimental noncentrosymmetric crystal structures in the Inorganic Crystal Structure Database (ICSD). Totally 46 Weyl semimetals were discovered to have nearly clean Fermi surface and Weyl points near Fermi level within 300 meV, and 9 of them are chiral structures which may host the quantized circular photogalvanic effect. In addition, the nonlinear optical response is studied and giant shift current is explored in the end. Besides nonmagnetic WSMs, our powerful tools can also be used in the discovery of magnetic topological materials.
- arXiv:1911.10331 (replaced) [pdf, other]
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Title: Prethermal memory loss in interacting quantum systems coupled to thermal bathsSubjects: Disordered Systems and Neural Networks (cond-mat.dis-nn); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Quantum Gases (cond-mat.quant-gas)
We study the relaxation dynamics of an extended Fermi-Hubbard chain with a strong Wannier-Stark potential tilt coupled to a bath. When the system is subjected to dephasing noise, starting from a pure initial state the system's total von Neumann entropy is found to grow monotonously. The scenario becomes rather different when the system is coupled to a thermal bath of finite temperature. Here, for sufficiently large field gradients and initial energies, the entropy peaks in time and almost reaches its largest possible value (corresponding to the maximally mixed state), long before the system relaxes to thermal equilibrium. This entropy peak signals a prethermal memory loss and, relative to the time where it occurs, the system is found to exhibit a simple scaling behavior in space and time. By comparing the system's dynamics to that of a simplified model, the underlying mechanism is found to be related to the localization property of the Wannier-Stark system, which favors dissipative coupling between eigenstates that are close in energy.
- arXiv:1912.08236 (replaced) [pdf, other]
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Title: Bose-glass phase of a one-dimensional disordered Bose fluid: metastable states, quantum tunneling and dropletsComments: v2) 21 pages, 10 figures; added coauthor, revised discussion on the quantum boundary layer and additional comment on the need of a nonperturbative FRG approach. arXiv admin note: text overlap with arXiv:1903.12374 v3) close to published versionJournal-ref: Phys. Rev. E 101, 042139 (2020)Subjects: Quantum Gases (cond-mat.quant-gas)
We study a one-dimensional disordered Bose fluid using bosonization, the replica method and a nonperturbative functional renormalization-group approach. We find that the Bose-glass phase is described by a fully attractive strong-disorder fixed point characterized by a singular disorder correlator whose functional dependence assumes a cuspy form that is related to the existence of metastable states. At nonzero momentum scale $k$, quantum tunneling between the ground state and low-lying metastable states leads to a rounding of the cusp singularity into a quantum boundary layer (QBL). The width of the QBL depends on an effective Luttinger parameter $K_k\sim k^\theta$ that vanishes with an exponent $\theta=z-1$ related to the dynamical critical exponent $z$. The QBL encodes the existence of rare "superfluid" regions, controls the low-energy dynamics and yields a (dissipative) conductivity vanishing as $\omega^2$ in the low-frequency limit. These results reveal the glassy properties (pinning, "shocks" or static avalanches) of the Bose-glass phase and can be understood within the "droplet" picture put forward for the description of glassy (classical) systems.
- arXiv:2001.01938 (replaced) [pdf, other]
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Title: Evidence for an orbital dependent Mott transition in the ladders of (La,Ca)$_x$Sr$_{14-x}$Cu$_{24}$O$_{41}$ derived by electron energy-loss spectroscopyJournal-ref: Phys. Rev. B 101, 195132 (2020)Subjects: Superconductivity (cond-mat.supr-con); Strongly Correlated Electrons (cond-mat.str-el)
The knowledge of the charge carrier distribution among the different orbitals of Cu and O is a precondition for the understanding of the physical properties of various Cu-O frameworks. We employ electron energy-loss spectroscopy to elucidate the charge carrier plasmon dispersion in (La, Ca)$_x$Sr$_{14-x}$Cu$_{24}$O$_{41}$ in dependency of $x$ as well as temperature. We observe that the energy of the plasmon increases upon increasing Ca content, which signals an internal charge redistribution between the two Cu-O subsystems. Moreover, contrary to an uncorrelated model we come to the conclusion that the holes transferred to the Cu$_2$O$_3$ ladders are mainly located in the bonding and not in the anti-bonding band. This is caused by an orbital dependent Mott transition.
- arXiv:2001.06692 (replaced) [pdf, ps, other]
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Title: Density Density Correlation Function of Strongly Inhomogeneous Luttinger LiquidsComments: 22 pagesSubjects: Strongly Correlated Electrons (cond-mat.str-el)
In this work, we show in pedagogical detail that the most singular contributions to the slow part of the asymptotic density-density correlation function of Luttinger liquids with fermions interacting mutually with only short-range forward scattering and also with localised scalar static impurities (where backward scattering takes place) has a compact analytical expression in terms of simple functions that have second order poles and involve only the scale-independent bare transmission and reflection coefficients. This proof uses conventional fermionic perturbation theory resummed to all orders, together with the idea that for such systems, the (connected) moments of the density operator all vanish beyond the second order - the odd ones vanish identically and the higher order even moments are less singular than the second order moment which is the only one included. This important result is the crucial input to the recently introduced "Non-Chiral Bosonization Technique" (NCBT) to study such systems. The results of NCBT cannot be easily compared with the results obtained using conventional bosonization as the former only extracts the most singular parts of the correlation functions albeit for arbitrary impurity strengths and mutual interactions. The latter, ambitiously attempts to study all the parts of the asymptotic correlation functions and is thereby unable to find simple analytical expressions and is forced to operate in the vicinity of the homogeneous system or the half line (the opposite extreme). For a fully homogeneous system or its antithesis viz. the half-line, all the higher order connected moments of the density vanish identically which means the results of chiral bosonization and NCBT ought to be the same and indeed they are.
- arXiv:2001.06728 (replaced) [pdf, other]
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Title: Big-Data Science in Porous Materials: Materials Genomics and Machine LearningComments: Editorial changes (typos fixed, minor adjustments to figures)Subjects: Materials Science (cond-mat.mtrl-sci); Machine Learning (cs.LG)
By combining metal nodes with organic linkers we can potentially synthesize millions of possible metal organic frameworks (MOFs). At present, we have libraries of over ten thousand synthesized materials and millions of in-silico predicted materials. The fact that we have so many materials opens many exciting avenues to tailor make a material that is optimal for a given application. However, from an experimental and computational point of view we simply have too many materials to screen using brute-force techniques. In this review, we show that having so many materials allows us to use big-data methods as a powerful technique to study these materials and to discover complex correlations. The first part of the review gives an introduction to the principles of big-data science. We emphasize the importance of data collection, methods to augment small data sets, how to select appropriate training sets. An important part of this review are the different approaches that are used to represent these materials in feature space. The review also includes a general overview of the different ML techniques, but as most applications in porous materials use supervised ML our review is focused on the different approaches for supervised ML. In particular, we review the different method to optimize the ML process and how to quantify the performance of the different methods. In the second part, we review how the different approaches of ML have been applied to porous materials. In particular, we discuss applications in the field of gas storage and separation, the stability of these materials, their electronic properties, and their synthesis. The range of topics illustrates the large variety of topics that can be studied with big-data science. Given the increasing interest of the scientific community in ML, we expect this list to rapidly expand in the coming years.
- arXiv:2001.11562 (replaced) [pdf, ps, other]
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Title: Mass-dependencies of the bound state properties for three-body positronium-like exitonic complexesAuthors: Alexei M. FrolovSubjects: Atomic Physics (physics.atom-ph); Other Condensed Matter (cond-mat.other)
Mass-dependencies of a number of bound state properties are investigated in some light two-electron exitonic complexes (or clusters) $Z^{+} e^{-} e^{-}$, where $m_e \le m_Z \le 2 m_e$. These exitonic complexes (or model ions) play a great role in modern solid state physics, since such complexes describe optical absorption in a number of semiconductors. We also derived and tested a number of accurate mass-interpolation formulas for these properties. In general, our mass-interpolation formulas allow one to predict (fast and accurately) numerical values of these bound state properties in the `new' exitonic complexes, i.e., in three-body exitonic complexes with new mass ratios.
- arXiv:2002.04431 (replaced) [pdf, other]
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Title: Loss of ultracold RbCs molecules via optical excitation of long-lived two-body collision complexesComments: 6 pages, 4 figuresJournal-ref: Phys. Rev. Lett. 124, 163402 (2020)Subjects: Atomic Physics (physics.atom-ph); Quantum Gases (cond-mat.quant-gas)
We show that the lifetime of ultracold ground-state $^{87}$Rb$^{133}$Cs molecules in an optical trap is limited by fast optical excitation of long-lived two-body collision complexes. We partially suppress this loss mechanism by applying square-wave modulation to the trap intensity, such that the molecules spend 75% of each modulation cycle in the dark. By varying the modulation frequency, we show that the lifetime of the collision complex is $0.53\pm0.06$ ms in the dark. We find that the rate of optical excitation of the collision complex is $3^{+4}_{-2}\times10^{3}$ W$^{-1}$ cm$^2$ s$^{-1}$ for $\lambda = 1550$ nm, leading to a lifetime of <100 ns for typical trap intensities. These results explain the two-body loss observed in experiments on nonreactive bialkali molecules.
- arXiv:2002.10446 (replaced) [pdf, other]
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Title: Electronic structural critique of interesting thermal and optical properties of C$_{17}$Ge germagrapheneJournal-ref: Phys. Chem. Chem. Phys., 2020,22, 8606-8615Subjects: Materials Science (cond-mat.mtrl-sci); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Computational Physics (physics.comp-ph)
In this communication, we report a theoretical attempt to understand the involvement of electronic structure in determination of optical and thermal properties of C$_{17}$Ge germagraphene, a buckled two dimensional material. The structure is found to be a direct bandgap semiconductor with low carrier effective mass. Our study has revealed that the effect of spin-orbit coupling on the band structure and in appearance of spin Hall current in the material. A selectively high blue to ultraviolet light absorption and a refractive index comparable to flint glass open up the possible applicability of this material for optoelectronic devices. From electronic structural point of view, we investigate the reason behind its moderately high Seebeck coefficient and power factor comparable to traditional thermoelectric materials. Besides its narrow bandgap, relatively smaller work function of C$_{17}$Ge ($4.361 ~eV$) than graphene ($4.390 ~eV$) and germanene ($4.682 ~eV$) assures more easily removal of electron from the surface. This material is turned out to be an excellent alternative for futuristic semiconductor application from optical to thermal device regime.
- arXiv:2003.01419 (replaced) [pdf, other]
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Title: Vibrational quenching of cold molecular ions immersed in their parent gasComments: Applied Sciences Special Issue "Optical Trapping of Ions and Atoms 2020: Novel Advances and Prospects"Journal-ref: Appl. Sci. 10, 2371 (2020)Subjects: Atomic Physics (physics.atom-ph); Quantum Gases (cond-mat.quant-gas); Quantum Physics (quant-ph)
Hybrid ion-atom systems provide an excellent platform for studies of state-resolved quantum chemistry at low temperatures, where quantum effects may be prevalent. Here we study theoretically the process of vibrational relaxation of an initially weakly bound molecular ion due to collisions with the background gas atoms. We show that this inelastic process is governed by the universal long-range part of the interaction potential, which allows for using simplified model potentials applicable to multiple atomic species. The product distribution after the collision can be estimated by making use of the distorted wave Born approximation. We find that the inelastic collisions lead predominantly to small changes in the binding energy of the molecular ion.
- arXiv:2003.05163 (replaced) [pdf, other]
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Title: Correlations in the elastic Landau level of a graphene/NbSe$_2$ van der Waals heterostructureAuthors: Antonio L. R. Manesco, Jose L. Lado, Eduardo V. Ribeiro, Gabrielle Weber, Durval Rodrigues JrComments: 6 pages, 5 figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Electronic correlations stemming from nearly flat bands in van der Waals materials have demonstrated to be a powerful playground to engineer artificial quantum matter, including superconductors, correlated insulators and topological matter. This phenomenology has been experimentally observed in a variety of twisted van der Waals materials, such as graphene and dichalcogenide multilayers. Here we show that a hybrid graphene/dichalcogenide multilayer can yield a correlated state, emerging from an elastic pseudo Landau level. Our results build on top of recent experimental findings reporting that, when placed on top of a NbSe$_2$ substrate, graphene sheets relax forming a periodic, long-range buckling pattern caused by the lattice mismatch. The low-energy physics can be accurately described by electrons in the presence of a pseudo-axial gauge field, leading to the formation of sublattice-polarized Landau levels. Moreover, we verify that the high density of states at the zeroth Landau level leads to the formation of a periodically modulated ferrimagnetic groundstate, which can be controlled by the application of external electric fields. Our results indicate that van der Waals heterostructures combining graphene and dichalcogenides are a versatile platform to explore emergent electronic states arising from correlated elastic Landau levels.
- arXiv:2003.09743 (replaced) [pdf, other]
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Title: Low-temperature asymptotic of the transverse dynamical structure factor for a magnetically polarized XX chainAuthors: P.N. BibikovComments: 32 pages, 6 figuresSubjects: Strongly Correlated Electrons (cond-mat.str-el)
Dyson equation for the real two-time commutator retarded one-magnon Green function of the ferromagnetically polarized XX chain is suggested following the Plakida-Tserkovnikov algorithm. Starting from this result a low-temperature integral representation for the corresponding magnon self energy is obtained by the truncated form factor expansion however without any resummations. Within the suggested approach the low-temperature asymptotics of the transverse dynamical structure factor may be readily studied. Some obtained line shapes are presented.
- arXiv:2003.09766 (replaced) [pdf, other]
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Title: Subsystem Rényi Entropy of Thermal Ensembles for SYK-like modelsComments: 20 pages, 4 figuresSubjects: Strongly Correlated Electrons (cond-mat.str-el); Quantum Physics (quant-ph)
The Sachdev-Ye-Kitaev model is an $N$-modes fermionic model with infinite range random interactions. In this work, we study the thermal R\'enyi entropy for a subsystem of the SYK model using the path-integral formalism in the large-$N$ limit. The results are consistent with exact diagonalization [1] and can be well approximated by thermal entropy with an effective temperature [2] when subsystem size $M\leq N/2$. We also consider generalizations of the SYK model with quadratic random hopping term or $U(1)$ charge conservation.
- arXiv:2003.09804 (replaced) [pdf, ps, other]
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Title: Origin of superconductivity and giant phonon softening in TlInTe$_2$ under pressureAuthors: Sorb Yesudhas, N. Yedukondalu, Manoj K. Jana, Jianbo Zhang, Jie Huang, Bijuan Chen, Hongshang Deng, Raimundas Sereika, Hong Xiao, Stanislav Sinogeikin, Curtis Kenney-Benson, Kanishka Biswas, John B. Parise, Yang Ding, Ho-kwang MaoComments: 43 pages (27 pages for main text and 16 pages for SI), 20 figures (5 in main text and 15 in SI)Subjects: Superconductivity (cond-mat.supr-con)
Analogous to 2D layered transition metal dichalcogenides, the TlSe family of 1D chain materials with Zintl-type structure exhibits exotic phenomena under high-pressure. In the present work, we have systematically investigated the high-pressure behavior of TlInTe 2 using Raman spectroscopy, synchrotron X-ray diffraction, and transport measurements, in combination with crystal structure prediction (CSP) based on the evolutionary approach and first principles calculations. We found that TlInTe$_2$ undergoes a pressure driven semiconductor to semimetal transition at 4 GPa, followed by a superconducting transition at 5.7 GPa (with Tc = 3.8 K) induced by a Lifshitz transition. The Lifshitz transition is initiated by the appearance of new electron pockets on the Fermi surface, which evolve with pressure and connect to the adjacent electron pockets forming an umbrella shaped Fermi surface at the top and bottom of the Brillouin zone. An unusual giant phonon softening (Ag mode) concomitant with a V-shaped Tc behavior appears at 10-12 GPa as a result of the interaction of optical phonons with the conduction electrons, resulting in Fano line shaped asymmetry in Ag mode. A prominent Tc anomaly concurrent with the Ag mode softening at 19-20 GPa is correlated to the semimetal to metal transition. The CSP calculations reveal that these transitions are not accompanied by any structural phase transitions up to the maximum pressure achieved, 33.5 GPa. Our findings on TlInTe$_2$ open up a new platform to study a plethora of unexplored high pressure novel phenomena in TlSe family induced by Lifshitz transition (electronic driven), phonon softening and electron-phonon coupling.
- arXiv:2003.10722 (replaced) [pdf]
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Title: Theoretical correction methods for optical tweezers: Acquisition of potentials of mean forces between colloidal particles in a bulk and on a surfaceComments: 15 pages and 1 figure. In version 2, each H in Eqs. (30)-(32) has been corrected to H0. In version 3, a typographical error in Eq. (12) is correctedSubjects: Soft Condensed Matter (cond-mat.soft); Data Analysis, Statistics and Probability (physics.data-an); Optics (physics.optics)
It is known that line optical tweezers (LOT) can measure potential of mean force (PMF) between colloidal particles in the bulk. However, PMF obtained with LOT is empirically modified before showing the result of the final form in order to correct the potential rise at long distances. In the present letter, we derive theoretical correction methods for acquisition of PMF by using statistical mechanics. Using the new methods, PMF can be obtained without the empirical fitting equation. Through the new methods, external potential acting on the trapped two colloidal particles induced by LOT can also be obtained. As an additional study, we explain a method for obtaining PMF between colloidal particles on a substrate surface, in which a normal optical tweezers with a fixed focal point is used. This method can also obtain the external potential acting on the trapped two colloidal particles existing on the surface.
- arXiv:2003.10789 (replaced) [pdf, other]
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Title: Collective Modes in Excitonic Insulators: Effects of Electron-Phonon Coupling and Signatures in Optical ResponseComments: 19 pages, 13 figuresJournal-ref: Phys. Rev. B 101, 195118 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We consider a two-band spinless model describing an excitonic insulator (EI) on the two-dimensional square lattice with anisotropic hopping parameters and electron-phonon (el-ph) coupling, inspired by the EI candidate Ta$_2$NiSe$_5$. We systematically study the nature of the collective excitations in the ordered phase which originates from the interband Coulomb interaction and the el-ph coupling. When the ordered phase is stabilized only by the Coulomb interaction (pure EI phase), its collective response exhibits a massless phase mode in addition to the amplitude mode. We show that in the BEC regime, the signal of the amplitude mode becomes less prominent and that the anisotropy in the phase mode velocities is relaxed compared to the model bandstructure. Through coupling to the lattice, the phase mode acquires a mass and the signal of the amplitude mode becomes less prominent. Importantly, character of the softening mode at the boundary between the normal semiconductor phase and the ordered phase depends on the parameter condition. In particular, we point out that even for el-ph coupling smaller than the Coulomb interaction the mode that softens to zero at the boundary can have a phonon character. We also discuss how the collective modes can be observed in the optical conductivity. Furthermore, we study the effects of nonlocal interactions on the collective modes and show the possibility of realizing a coexistence of an in-gap mode and an above-gap mode split off from the single amplitude mode in the system with the local interaction only.
- arXiv:2003.10799 (replaced) [pdf, other]
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Title: Imaging the coherent propagation of collective modes in the excitonic insulator candidate Ta$_2$NiSe$_5$ at room temperatureAuthors: Paolo Andrich, Hope M. Bretscher, Yuta Murakami, Denis Golež, Benjamin Remez, Prachi Telang, Anupam Singh, Luminita Harnagea, Nigel R. Cooper, Andrew J. Millis, Philipp Werner, A. K. Sood, Akshay RaoComments: Updated citationsSubjects: Strongly Correlated Electrons (cond-mat.str-el); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Excitonic insulating (EI) materials are predicted to host a condensate of electron-hole pairs in their ground state, giving rise to collective many-body effects. Although several bulk materials have been proposed as EIs recently, a direct observation of the characteristic collective behavior is still missing. Here, we use ultrafast, spatially-resolved, pump-probe microscopy to investigate the propagation of photoinduced excitations in a proposed EI, Ta$_2$NiSe$_5$. Below the critical temperature for the EI phase (328 K), we observe the propagation, for distances of up to 1 $\mu$m, of coherent oscillatory modes in the THz range at velocities of the order of 10$^5$ m/s. We develop a theoretical framework to explain these findings and suggest that this behavior results from the hybridization of phonon modes with the phase mode of the EI. We infer that the ordered EI phase is driven predominantly by interorbital Coulomb interactions and that this system falls into the BCS-BEC crossover regime. This study provides a route for the investigation of collective properties in strongly correlated materials and paves the way for applications that can take advantage of these quantum phenomena up to room temperature.
- arXiv:2003.10836 (replaced) [pdf, other]
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Title: Effects of Disorder on the Transport of Collective Modes in an Excitonic CondensateComments: 21 pages, 10 figures. v2: Added reference to concurrent preprintSubjects: Strongly Correlated Electrons (cond-mat.str-el); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
An excitonic insulator (EI) is an unconventional quantum phase of matter in which excitons, bound pairs of electrons and holes, undergo Bose--Einstein condensation, forming a macroscopic coherent state. While its existence was first hypothesized half a century ago, the EI has eluded experimental observation in bulk materials for decades. In the last few years, a resurgence of interest in the subject has been driven by the identification of several candidate materials suspected to support an excitonic condensate. However, one obstacle in verifying the nature of these systems has been to find signatures of the EI that distinguish it from a normal insulator. To address this, we focus on a clear qualitative difference between the two phases: the existence of Goldstone modes born by the spontaneous breaking of a $U(1)$ symmetry in the EI. Even if this mode is gapped, as occurs in the case of an approximate symmetry, this branch of collective modes remains a fundamental feature of the low-energy dynamics of the EI provided the symmetry-breaking is small. We study a simple model that realizes an excitonic condensate, and use mean field theory within the random-phase approximation to determine its collective modes. We subsequently develop a diagrammatic method to incorporate the effects of disorder perturbatively, and use it to determine the scattering rate of the collective modes. We interpret our results within an an effective field theory. The collective modes are found to be robust against symmetry-preserving disorder, implying an experimental fingerprint unique to the EI: the ballistic propagation of low-lying modes over mesoscopic distances, at electronic-scale velocities. We suggest this could affect thermal transport at low temperatures, and could be observed via spatially-resolved pump-probe spectroscopy through the coherent response of phonons that hybridize with the collective modes.
- arXiv:1502.07807 (replaced) [pdf, ps, other]
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Title: RC-circuit-like dynamic characteristic of the magnetic domain wall in ferromagnetic nanowiresComments: 16 pages, 4 figuresJournal-ref: Chin. Phys. Lett. Vol. 32 Issue (08) 2015Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We have investigated dynamic behaviors of the magnetic domain wall under perpendicular magnetic field pulses in ferromagnetic nanowires using micromagnetic simulations. It has been found that the perpendicular magnetic field pulse can trigger the magnetic domain wall motion, where all the field torques are kept to be on the plane of nanowire strip. The magnetic domain wall speed faster than several hundreds meters per second is predicted without the Walker breakdown for the perpendicular magnetic driving field stronger than $200~\mathrm{mT}$. Interestingly, the dynamic behavior of the moving magnetic domain wall driven by perpendicular magnetic field pulses is explained by charging- and discharging-like behaviors of an electrical RC-circuit model, where the charging and the discharging of "magnetic charges" on the nanowire planes are considered. The concept of the RC-model-like dynamic characteristic of the magnetic domain wall might be promising for spintronic functional device applications based on the magnetic domain wall motion.
- arXiv:1806.06753 (replaced) [pdf]
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Title: Anomalous Nernst effect beyond the magnetization scaling relation in the ferromagnetic Heusler compound Co$_2$MnGaAuthors: Satya N. Guin, Kaustuv Manna, Jonathan Noky, Sarah J. Watzman, Chenguang Fu, Nitesh Kumar, Walter Schnelle, Chandra Shekhar, Yan Sun, Johannes Gooth, Claudia FelserJournal-ref: NPG Asia Materials 2019Subjects: Materials Science (cond-mat.mtrl-sci)
Applying a temperature gradient in a magnetic material generates a voltage that is perpendicular to both the heat flow and the magnetization. This is the anomalous Nernst effect (ANE) which was thought to be proportional to the value of the magnetization for a long time. However, more generally, the ANE has been predicted to originate from a net Berry curvature of all bands near the Fermi level. Subsequently, a large anomalous Nernst thermopower has recently been observed in topological materials with no net magnetization but large net Berry curvature around E$_F$. These experiments clearly fall outside the scope of the conventional magnetization-model of the ANE, but a significant question remains: Can the value of the ANE in topological ferromagnets exceed the highest values observed in conventional ferromagnets? Here, we report a remarkably high anomalous Nernst thermopower value of ~6.0 \mu V/K at 1 T in the ferromagnetic topological Heusler compound Co$_2$MnGa at room temperature, which is around 7-times larger than any anomalous Nernst thermopower value ever reported for a conventional ferromagnet. Combined electrical, thermoelectric and first-principles calculations reveal that this high value of the ANE arises from a large net Berry curvature near the Fermi level associated with nodal lines and Weyl points.
- arXiv:1806.07879 (replaced) [pdf, ps, other]
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Title: Integrated information in the thermodynamic limitComments: arXiv admin note: substantial text overlap with arXiv:1805.00393Subjects: Neurons and Cognition (q-bio.NC); Disordered Systems and Neural Networks (cond-mat.dis-nn); Statistical Mechanics (cond-mat.stat-mech); Adaptation and Self-Organizing Systems (nlin.AO); Biological Physics (physics.bio-ph)
The capacity to integrate information is a prominent feature of biological and cognitive systems. Integrated Information Theory (IIT) provides a mathematical approach to quantify the level of integration in a system, yet its computational cost generally precludes its applications beyond relatively small models. In consequence, it is not yet well understood how integration scales up with the size of a system or with different temporal scales of activity, nor how a system maintains its integration as its interacts with its environment. Here, we show for the first time how measures of information integration scale when systems become very large. Using kinetic Ising models and mean-field approximations from statistical mechanics, we show that information integration diverges in the thermodynamic limit at certain critical points. Moreover, by comparing different divergent tendencies of blocks of a system at these critical points, we delimit the boundary between an integrated unit and its environment. Finally, we present a model that adaptively maintains its integration despite changes in its environment by generating a critical surface where its integrity is preserved. We argue that the exploration of integrated information for these limit cases helps in addressing a variety of poorly understood questions about the organization of biological, neural, and cognitive systems.
- arXiv:1812.07930 (replaced) [pdf, other]
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Title: Fermionic time-reversal symmetry in a photonic topological insulatorAuthors: Lukas J. Maczewsky, Bastian Höckendorf, Mark Kremer, Tobias Biesenthal, Matthias Heinrich, Andreas Alvermann, Holger Fehske, Alexander SzameitJournal-ref: Nature Materials (2020)Subjects: Optics (physics.optics); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Much of the recent enthusiasm directed towards topological insulators as a new state of matter is motivated by their hallmark feature of protected chiral edge states. In fermionic systems, Kramers degeneracy gives rise to these entities in the presence of time-reversal symmetry (TRS). In contrast, bosonic systems obeying TRS are generally assumed to be fundamentally precluded from supporting edge states. In this work, we dispel this perception and experimentally demonstrate counter-propagating chiral states at the edge of a time-reversal-symmetric photonic waveguide structure. The pivotal step in our approach is encoding the effective spin of the propagating states as a degree of freedom of the underlying waveguide lattice, such that our photonic topological insulator is characterised by a $\mathbb{Z}_2$-type invariant. Our findings allow for fermionic properties to be harnessed in bosonic systems, thereby opening new avenues for topological physics in photonics as well as acoustics, mechanics and even matter waves.
- arXiv:1902.08818 (replaced) [pdf]
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Title: Deep Learning-Guided Surface Characterization for Autonomous Hydrogen LithographyAuthors: Mohammad Rashidi, Jeremiah Croshaw, Kieran Mastel, Marcus Tamura, Hedieh Hosseinzadeh, Robert A. WolkowJournal-ref: Mach. Learn.: Sci. Technol. 1 025001 (2020)Subjects: Materials Science (cond-mat.mtrl-sci)
As the development of atom scale devices transitions from novel, proof-of-concept demonstrations to state-of-the-art commercial applications, automated assembly of such devices must be implemented. Here we present an automation method for the identification of defects prior to atomic fabrication via hydrogen lithography using deep learning. We trained a convolutional neural network to locate and differentiate between surface features of the technologically relevant hydrogen-terminated silicon surface imaged using a scanning tunneling microscope. Once the positions and types of surface features are determined, the predefined atomic structures are patterned in a defect-free area. By training the network to differentiate between common defects we are able to avoid charged defects as well as edges of the patterning terraces. Augmentation with previously developed autonomous tip shaping and patterning modules allows for atomic scale lithography with minimal user intervention.
- arXiv:1906.10146 (replaced) [pdf, other]
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Title: Fluctuations and Higgs mechanism in Under-Doped Cuprates: a ReviewComments: To be published in Annual Review of Condensed Matter PhysicsJournal-ref: Annual Review of Condensed Matter Physics 2020 11:1, 301-323Subjects: Superconductivity (cond-mat.supr-con)
The physics of the pseudo-gap phase of high temperature cuprate superconductors has been an enduring mystery in the past thirty years. The ubiquitous presence of the pseudo-gap phase in under-doped cuprates suggests that its understanding holds a key in unraveling the origin of high temperature superconductivity. In this paper, we review various theoretical approaches to this problem, with a special emphasis on the concept of emergent symmetries in the under-doped region of those compounds. We differentiate the theories by considering a few fundamental questions related to the rich phenomenology of these materials. Lastly we discuss a recent idea of two kinds of entangled preformed pairs which open a gap at the pseudo-gap onset temperature $T^{*}$ through a specific Higgs mechanism. We give a review of the experimental consequences of this line of thoughts.
- arXiv:1906.10597 (replaced) [pdf, other]
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Title: Bandgap-Assisted Quantum Control of Topological Edge States in a CavityComments: 7+15 pages, 5+11 figures, will appear in Physical Review ResearchJournal-ref: Phys. Rev. Research 2, 012076 (2020)Subjects: Quantum Physics (quant-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Quantum matter with exotic topological order has potential applications in quantum computation. However, in present experiments, the manipulations on topological states are still challenging. We here propose an architecture for optical control of topological matter. We consider a topological superconducting qubit array with Su-Schrieffer-Heeger (SSH) Hamiltonian which couples to a microwave cavity. Based on parity properties of the topological qubit array, we propose an optical spectroscopy method to observe topological phase transition, i.e., edge-to-bulk transition. This new method can be achieved by designing cavity-qubit couplings. A main purpose of this work is to understand how topological phase transition affects light-matter interaction. We find that topological bandgap plays an essential role on this issue. In topological phase, the resonant vacuum Rabi splitting of degenerate edge states coupling to the cavity field is protected from those of bulk states by the bandgap. In dispersive regime, the cavity induced coupling between edge states is dominant over couplings between edge and bulk states, due to the topological bandgap. As a result, quantum interference between topological edge states occures and enables single-photon transport through boundaries of the topological qubit array. Our work may pave a way for topological quantum state engineering.
- arXiv:1910.12750 (replaced) [pdf]
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Title: Deep-Learning-Based Image Segmentation Integrated with Optical Microscopy for Automatically Searching for Two-Dimensional MaterialsAuthors: Satoru Masubuchi, Eisuke Watanabe, Yuta Seo, Shota Okazaki, Takao Sasagawa, Kenji Watanabe, Takashi Taniguchi, Tomoki MachidaJournal-ref: npj 2D Mater Appl 4, 3 (2020)Subjects: Image and Video Processing (eess.IV); Materials Science (cond-mat.mtrl-sci)
Deep-learning algorithms enable precise image recognition based on high-dimensional hierarchical image features. Here, we report the development and implementation of a deep-learning-based image segmentation algorithm in an autonomous robotic system to search for two-dimensional (2D) materials. We trained the neural network based on Mask-RCNN on annotated optical microscope images of 2D materials (graphene, hBN, MoS2, and WTe2). The inference algorithm is run on a 1024 x 1024 px2 optical microscope images for 200 ms, enabling the real-time detection of 2D materials. The detection process is robust against changes in the microscopy conditions, such as illumination and color balance, which obviates the parameter-tuning process required for conventional rule-based detection algorithms. Integrating the algorithm with a motorized optical microscope enables the automated searching and cataloging of 2D materials. This development will allow researchers to utilize unlimited amounts of 2D materials simply by exfoliating and running the automated searching process.
- arXiv:1911.05891 (replaced) [pdf, other]
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Title: Dynamical dimerization phase in Jaynes-Cummings latticesComments: 10 pages, 7 figures. We have included new results for the open system dynamics. Accepted for publication in New Journal of PhysicsJournal-ref: New J. Phys. (2020) 033034Subjects: Quantum Physics (quant-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We report on an emergent dynamical phase of a strongly-correlated light-matter system, which is governed by dimerization processes due to short-range and long-range two-body interactions. The dynamical phase is characterized by the spontaneous symmetry breaking of the translational invariance and appears in an intermediate regime of light-matter interaction between the resonant and dispersive cases. We describe the quench dynamics from an initial state with integer filling factor of a finite-sized array of coupled resonators, each doped with a two-level system, in a closed and open scenario. The closed system dynamics has an effective Hilbert space description that allows us to demonstrate and characterize the emergent dynamical phase via time-averaged quantities, such as fluctuations in the number of polaritons per site and linear entropy. We prove that the dynamical phase is governed by intrinsic two-body interactions and the lattice topological structure. In the open system dynamics, we show evidence about the robustness of dynamical dimerization processes under loss mechanisms. Our findings can be used to determine the light-matter detuning range, where the dimerized phase emerges.
- arXiv:1911.07651 (replaced) [pdf, ps, other]
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Title: Self-consistent two-gap approach in studying multi-band superconductivity in NdFeAsO$_{0.65}$F$_{0.35}$Authors: Ritu Gupta, Alexander Maisuradze, Nikolai D. Zhigadlo, Hubertus Luetkens, Alex Amato, Rustem KhasanovComments: 10 pages, 8 figuresJournal-ref: Frontiers in Physics 8, 2 (2020)Subjects: Superconductivity (cond-mat.supr-con)
High-quality single crystals of NdFeAsO$_{0.65}$F$_{0.35}$ (the transition temperature $T_{\rm c} \simeq 30.6$~K) were studied in zero-field (ZF) and transverse-field (TF) muon-spin rotation/relaxation ($\mu$SR) experiments. An upturn in muon-spin depolarization rate at $T\lesssim 3$~K was observed in ZF-$\mu$SR measurements and it was associated with the onset of ordering of Nd electronic moments. Measurements of the magnetic field penetration depth ($\lambda$) were performed in the TF geometry. By applying the external magnetic field $B_{\rm ex}$ parallel to the crystallographic $c$-axis ($B_{\rm ex}\| c$) and parallel to the $ab$-plane ($B_{\rm ex}\| ab$), the temperature dependencies of the in-plane component ($\lambda_{ab}^{-2}$) and the combination of the in-plane and the out of plane components ($\lambda_{ab,c}^{-2}$) of the superfluid density were determined, respectively. The out-of-plane superfluid density component ($\lambda_{c}^{-2}$) was further obtained by combining the results of $B_{\rm ex} \| c$ and $B_{\rm ex} \| {ab}$ set of experiments. The temperature dependencies of $\lambda_{ab}^{-2}$, $\lambda_{ab,c}^{-2}$, and $\lambda_{c}^{-2}$ were analyzed within the framework of a self-consistent two-gap model despite of using the traditional $\alpha$-model. Interband coupling was taken into account, instead of assuming it to be zero as it stated in the $\alpha$-model. A relatively small value of the interband coupling constant $\Lambda_{12} \simeq 0.01$ was obtained, thus indicating that the energy bands in NdFeAsO$_{0.65}$F$_{0.35}$ are only weakly coupled. In spite of their small magnitude, the coupling between the bands leads to the single value of the superconducting transition temperature $T_{\rm c}$.
- arXiv:1912.00630 (replaced) [pdf]
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Title: Direct demonstration of topological stability of magnetic skyrmions via topology manipulationAuthors: Soong-Geun Je, Hee-Sung Han, Se Kwon Kim, Sergio A. Montoya, Weilun Chao, Ik-Sun Hong, Eric E. Fullerton, Ki-Suk Lee, Kyung-Jin Lee, Mi-Young Im, Jung-Il HongJournal-ref: ACS Nano 2020, 14, 3, 3251-3258Subjects: Materials Science (cond-mat.mtrl-sci)
Topological protection precludes a continuous deformation between topologically inequivalent configurations in a continuum. Motivated by this concept, magnetic skyrmions, topologically nontrivial spin textures, are expected to exhibit the topological stability, thereby offering a prospect as a nanometer-scale non-volatile information carrier. In real materials, however, atomic spins are configured as not continuous but discrete distribution, which raises a fundamental question if the topological stability is indeed preserved for real magnetic skyrmions. Answering this question necessitates a direct comparison between topologically nontrivial and trivial spin textures, but the direct comparison in one sample under the same magnetic fields has been challenging. Here we report how to selectively achieve either a skyrmion state or a topologically trivial bubble state in a single specimen and thereby show how robust the skyrmion structure is in comparison with the bubbles for the first time. We demonstrate that topologically nontrivial magnetic skyrmions show longer lifetimes than trivial bubble structures, evidencing the topological stability in a real discrete system. Our work corroborates the physical importance of the topology in the magnetic materials, which has hitherto been suggested by mathematical arguments, providing an important step towards ever-dense and more-stable magnetic devices.
- arXiv:1912.04040 (replaced) [pdf, other]
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Title: Nature of the 5$f$ electronic structure of plutoniumComments: 16 pages, 9 figuresJournal-ref: Phys. Rev. B 101, 125123 (2020)Subjects: Strongly Correlated Electrons (cond-mat.str-el); Materials Science (cond-mat.mtrl-sci)
Plutonium (Pu), in which the 5$f$ valence electrons always wander the boundary between localized and itinerant states, exhibits quite complex crystal structures and unprecedentedly anomalous properties with respect to temperature and alloying. Understanding its chemical and physical properties, especially its 5$f$ electronic structure is one of the central and unsolved topics in condensed matter theory. In the present work, the electronic structures of the six allotropes of Pu (including its $\alpha$, $\beta$, $\gamma$, $\delta$, $\delta'$, and $\epsilon$ phases) at ambient pressure are studied comprehensively by means of the density functional theory in combination with the single-site dynamical mean-field theory. The band structures, total and partial density of states, valence state histograms, 5$f$ orbital occupancies, X-ray branching ratios, and self-energy functions are carefully studied. It is suggested that the $\alpha$, $\beta$, and $\gamma$ phases of Pu are typical Racah metals in which the atomic multiple effect dominates near the Fermi level. The calculated results reveal that not only the $\delta$ phase, but also all the six allotropes are archetypal mixed-valence metals with remarkable atomic eigenstate fluctuation. In consequence of that, the 5$f$ occupancy $n_{5f}$ is around 5.1 $\sim$ 5.4, which varies with respect to the atomic volume and electronic correlation strength of Pu. The 5$f$ electronic correlation in Pu is moderately orbital-dependent. Moreover, the 5$f$ electrons in the $\delta'$ phase are the most correlated and localized.
- arXiv:1912.12391 (replaced) [pdf, other]
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Title: Theoretical Study of Magnetoelectric Effects in Honeycomb Antiferromagnet Co4Nb2O9Comments: 6 pages, 2 figures, to be published in JPS Conf. Proc. (2020), Proceedings of International Conference on Strongly Correlated Electron Systems 2019 (SCES-2019, Okayama, Japan)Subjects: Strongly Correlated Electrons (cond-mat.str-el); Materials Science (cond-mat.mtrl-sci)
The honeycomb antiferromagnet Co4Nb2O9 is known to exhibit an interesting magnetoelectric effect that the electric polarization rotates at the twice speed in the opposite direction relative to the rotation of the external magnetic field applied in the basal ab-plane. The spin-dependent electric dipole can be an origin of the magnetoelectric effect. It is described by the product of spin operators at different sites (type-I theory) or at the same site (type-II theory). We examine the electric polarization for the two cases on the basis of the symmetry analysis of the crystal structure of Co4Nb2O9, and conclude that the latter is the origin of the observed result. This paper also gives a general description of the field-induced electric polarization on honeycomb lattices with the C3 point group symmetry on the basis of the type-I theory.
- arXiv:2002.01814 (replaced) [pdf, ps, other]
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Title: Time-Energy Uncertainty Principle for Irreversible Heat EnginesComments: 15 pages, 4 figures, supplemental material 4 pages, accepted to Philos. Trans. R. Soc. AJournal-ref: Phil. Trans. R. Soc. A 378 (2020) 20190171Subjects: Statistical Mechanics (cond-mat.stat-mech); Atomic Physics (physics.atom-ph)
Even though irreversibility is one of the major hallmarks of any real life process, an actual understanding of irreversible processes remains still mostly semiempirical. In this paper we formulate a thermodynamic uncertainty principle for irreversible heat engines operating with an ideal gas as a working medium. In particular, we show that the time needed to run through such an irreversible cycle multiplied by the irreversible work lost in the cycle, is bounded from below by an irreducible and process-dependent constant that has the dimension of an action. The constant in question depends on a typical scale of the process and becomes comparable to Planck's constant at the length scale of the order Bohr-radius, i.e., the scale that corresponds to the smallest distance on which the ideal gas paradigm realistically applies.
- arXiv:2002.07636 (replaced) [pdf, ps, other]
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Title: Calculation of the biexciton shift in nanocrystals of inorganic perovskitesComments: 12 pages, 4 figuresJournal-ref: Phys. Rev. B 101, 125424 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We calculate the shift in emission frequency of the trion and biexciton (relative to that of the single exciton) for nanocrystals (NCs) of inorganic perovskites CsPbBr3 and CsPbI3. The calculations use an envelope-function k.p model combined with self-consistent Hartree-Fock and a treatment of the intercarrier correlation energy in the lowest (second) order of many-body perturbation theory. The carriers in the trion and biexciton are assumed to have relaxed nonradiatively to the ground state at the band edge before emission occurs. The theoretical trion shifts for both CsPbBr3 and CsPbI3 are found to be in fair agreement with available experimental data, which include low-temperature single-dot measurements, though are perhaps systematically small by a factor of order 1.5, which can plausibly be explained by a combination of a slightly overestimated dielectric constant and omitted third- and higher-order terms in the correlation energy. Taking this level of agreement into account, we estimate that the ground-state biexciton shift for CsPbBr3 is a redshift of order 10-20 meV for NCs with an edge-length of 12 nm. This value is intermediate among the numerous high-temperature measurements on NCs of CsPbBr3, which vary from large redshifts of order 100 meV to blueshifts of several meV.
- arXiv:2003.01510 (replaced) [pdf, other]
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Title: Ordering kinetics in q-state random-bond clock model: Role of Vortices and InterfacesJournal-ref: Phys. Rev. E 101, 032128 (2020)Subjects: Statistical Mechanics (cond-mat.stat-mech)
In this article, we present a Monte Carlo study of phase transition and coarsening dynamics in the non-conserved two-dimensional random-bond $q$-state clock model (RBCM) deriving from a pure clock model [Phys. Rev. E 98, 032109 (2018)]. Akin to the pure clock model, RBCM also passes through two different phases when quenched from a disordered initial configuration representing at infinite temperature. Our investigation of the equilibrium phase transition affirms that both upper ($T_c^1$) and lower ($T_c^2$) phase transition temperatures decrease with bond randomness strength $\epsilon$. Effect of $\epsilon$ on the non-equilibrium coarsening dynamics is investigated following independent rapid quenches in the quasi-long range ordered (QLRO, $T_c^2 < T < T_c^1$) regime and long-range ordered (LRO, $T<T_c^2$) regime at temperature $T$. We report that the dynamical scaling of the correlation function and structure factor are independent of $\epsilon$ and the presence of quenched disorder slows down domain coarsening. Coarsening dynamics in both LRO and QLRO regimes are further characterized by power-law growth with disorder-dependent exponents within our simulation time scales. The growth exponents in the LRO regime decreases from 0.5 in the pure case to 0.22 in the maximum disordered case, whereas the corresponding change in the QLRO regime happens from 0.45 to 0.38. We further explored the coarsening dynamics in the bond-diluted clock model and in both the models, the effect of the disorder is more significant for the quench in the LRO regime compared to the QLRO regime.
- arXiv:2003.05077 (replaced) [pdf, other]
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Title: Anisotropic three-dimensional weak localization in ultrananocrystalline diamond films with nitrogen inclusionsAuthors: L.H. Willems van Beveren, D.L. Creedon, N. Eikenberg, K. Ganesan, B.C. Johnson, G. Chimowa, D. Churochkin, S. Bhattacharyya, S. PrawerComments: 13 pages, 10 figuresJournal-ref: Phys. Rev. B 101, 115306 (2020)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We present a study of the structural and electronic properties of ultra-nanocrystalline diamond films that were modified by adding nitrogen to the gas mixture during chemical vapour deposition growth. Hall bar devices were fabricated from the resulting films to investigate their electrical conduction as a function of both temperature and magnetic field. Through low-temperature magnetoresistance measurements, we present strong evidence that the dominant conduction mechanism in these films can be explained by a combination of 3D weak localization (3DWL) and thermally activated hopping at higher temperatures. An anisotropic 3DWL model is then applied to extract the phase-coherence time as function of temperature, which shows evidence of a power law dependence in good agreement with theory.
Crosses
- arXiv:2003.09608 (cross-list from physics.chem-ph) [pdf]
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Title: Exposing Hidden Alternative Conformations of Small Flexible Molecules in 2D NMR Spectroscopy Using 1H-15N HMBCSubjects: Chemical Physics (physics.chem-ph); Materials Science (cond-mat.mtrl-sci)
Two-dimensional 1H-15N HMBC NMR spectra of a well-known anticonvulsant-carbamazepine-dissolved in chloroform, recorded on an NMR spectrometer and obtained from quantum-chemical calculations prove the existence of hidden conformers in saturated solutions. A weaker influence of ring currents was revealed for the hidden conformation of carbamazepine dissolved in saturated solution, which provides a simple approach for discovering hidden conformations. Hidden conformers were found in three different solvents: dimethyl sulfoxide, chloroform, and dichloromethane.
- arXiv:2003.09630 (cross-list from physics.chem-ph) [pdf]
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Title: High-pressure NMR spectroscopy in studies of the conformational composition of small molecules of ibuprofen in supercritical carbon dioxideSubjects: Chemical Physics (physics.chem-ph); Other Condensed Matter (cond-mat.other)
An experimental approach in conducting NMR measurements at supercritical parameters of state is discussed. A novel design of the high-pressure NMR cell was developed which allowed eliminating the field inhomogeneity and, thus, increasing the sensitivity of the experiment at the supercritical state. Analysis of the MD simulations and NMR data showed that two conformers of ibuprofen dominate in the solution in supercritical CO2 along the critical isochore 1.3 \r{ho}cr(CO2). Conformer populations calculated from MD simulations and from NMR spectra agree with each other
- arXiv:2003.10463 (cross-list from quant-ph) [pdf, other]
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Title: Quantum many-body dynamics of driven-dissipative Rydberg polaritonsComments: 5 pages, 5 figuresSubjects: Quantum Physics (quant-ph); Quantum Gases (cond-mat.quant-gas); Atomic Physics (physics.atom-ph)
We study the propagation of strongly interacting Rydberg polaritons through an atomic medium in a one-dimensional optical lattice. We derive an effective single-band Hubbard model to describe the dynamics of the dark state polaritons under realistic assumptions. Within this model, we analyze the driven-dissipative transport of polaritons through the system by considering a coherent drive on one side and by including the spontaneous emission of the metastable Rydberg state. Using a variational approch to solve the many-body problem, we find strong antibunching of the outgoing photons despite the losses from the Rydberg state decay.
- arXiv:2003.10814 (cross-list from cond-mat.soft) [pdf, other]
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Title: A jamming plane of sphere packingsComments: 19 pages, 20 figuresSubjects: Soft Condensed Matter (cond-mat.soft); Disordered Systems and Neural Networks (cond-mat.dis-nn); Statistical Mechanics (cond-mat.stat-mech)
The concept of jamming has attracted great research interest due to its broad relevance in soft matter such as liquids, glasses, colloids, foams, and granular materials, and its deep connection to the sphere packing problem and optimization problems. Here we show that the domain of amorphous jammed states of frictionless spheres can be significantly extended, from the well-known jamming-point at a fixed density, to a jamming-plane that spans the density and shear strain axes. We explore the jamming-plane, via athermal and thermal simulations of compression and shear jamming, with a help of an efficient swap algorithm to prepare initial equilibrium configurations. The jamming-plane can be divided into reversible-jamming and irreversible-jamming regimes, based on the reversibility of the route from the initial configuration to jamming. Our results suggest that the irreversible-jamming behavior reflects an escape from the meta-stable glass basin to which the initial configuration belongs to, or the absence of such basins. All jammed states, either compression or shear jammed, are isostatic, and exhibit jamming criticality of the same universality class. However, the anisotropy of contact networks non-trivially depends on the jamming density and strain. Among all state points on the jamming-plane, the jamming-point is a unique one with the minimum jamming density and the maximum randomness. For lattice packings, the jamming-plane shrinks into a single shear jamming-line that is independent of initial configurations. Our study paves the way for solving the long-standing random close packing problem, and provides a more complete framework to understand jamming.